[ID Refactor] Refactor ActorID, TaskID and ObjectID (#5286)

* Refactor ActorID, TaskID on the Java side.

Left a TODO comment

WIP for ObjectID

ADD test

Fix

Add java part

Fix Java test

Fix

Refine test.

Enable test in CI

* Extra a helper function.

* Resolve TODOs

* Fix Python CI

* Fix Java lint

* Update .travis.yml

Co-Authored-By: Stephanie Wang <swang@cs.berkeley.edu>

* Address some comments.

Address some comments.

Add id_specification.rst

Reanme id_specification.rst to id_specification.md

typo

Address zhijun's comments.

Fix test

Address comments.

Fix lint

Address comments

* Fix test

* Address comments.

* Fix build error

* Update src/ray/design_docs/id_specification.md

Co-Authored-By: Stephanie Wang <swang@cs.berkeley.edu>

* Update src/ray/design_docs/id_specification.md

Co-Authored-By: Stephanie Wang <swang@cs.berkeley.edu>

* Update src/ray/design_docs/id_specification.md

Co-Authored-By: Stephanie Wang <swang@cs.berkeley.edu>

* Update src/ray/design_docs/id_specification.md

Co-Authored-By: Stephanie Wang <swang@cs.berkeley.edu>

* Update src/ray/design_docs/id_specification.md

Co-Authored-By: Stephanie Wang <swang@cs.berkeley.edu>

* Address comments

* Update src/ray/common/id.h

Co-Authored-By: Stephanie Wang <swang@cs.berkeley.edu>

* Update src/ray/common/id.h

Co-Authored-By: Stephanie Wang <swang@cs.berkeley.edu>

* Update src/ray/common/id.h

Co-Authored-By: Stephanie Wang <swang@cs.berkeley.edu>

* Update src/ray/design_docs/id_specification.md

Co-Authored-By: Hao Chen <chenh1024@gmail.com>

* Update src/ray/design_docs/id_specification.md

Co-Authored-By: Hao Chen <chenh1024@gmail.com>

* Address comments.

* Address comments.

* Address comments.

* Update C++ part to make sure task id is generated determantic

* WIP

* Fix core worker

* Fix Java part

* Fix comments.

* Add Python side

* Fix python

* Address comments

* Fix linting

* Fix

* Fix C++ linting

* Add JobId() method to TaskID

* Fix linting

* Update src/ray/common/id.h

Co-Authored-By: Hao Chen <chenh1024@gmail.com>

* Update java/api/src/main/java/org/ray/api/id/TaskId.java

Co-Authored-By: Hao Chen <chenh1024@gmail.com>

* Update java/api/src/main/java/org/ray/api/id/TaskId.java

Co-Authored-By: Hao Chen <chenh1024@gmail.com>

* Update java/api/src/main/java/org/ray/api/id/ActorId.java

Co-Authored-By: Hao Chen <chenh1024@gmail.com>

* Address comments

* Add DriverTaskId embeding job id

* Fix tests

* Add python dor_fake_driver_id

* Address comments and fix linting

* Fix CI

.travis.yml

@@ -149,9 +149,6 @@ install:
   - ./ci/suppress_output ./ci/travis/install-cython-examples.sh
 
   - ./ci/suppress_output bash src/ray/test/run_gcs_tests.sh
-  # stats test.
-  - ./ci/suppress_output bazel build //:stats_test -c opt
-  - ./bazel-bin/stats_test
 
   # core worker test.
   - ./ci/suppress_output bash src/ray/test/run_core_worker_tests.sh

BUILD.bazel

@@ -487,6 +487,16 @@ cc_test(
     ],
 )
 
+cc_test(
+    name = "id_test",
+    srcs = ["src/ray/common/id_test.cc"],
+    copts = COPTS,
+    deps = [
+        "ray_common",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
 cc_test(
     name = "logging_test",
     srcs = ["src/ray/util/logging_test.cc"],

java/api/src/main/java/org/ray/api/Checkpointable.java

@@ -1,6 +1,8 @@
 package org.ray.api;
 
 import java.util.List;
+
+import org.ray.api.id.ActorId;
 import org.ray.api.id.UniqueId;
 
 public interface Checkpointable {
@@ -10,7 +12,7 @@ public interface Checkpointable {
     /**
      * Actor's ID.
      */
-    public final UniqueId actorId;
+    public final ActorId actorId;
     /**
      * Number of tasks executed since last checkpoint.
      */
@@ -20,8 +22,8 @@ public interface Checkpointable {
      */
     public final long timeElapsedMsSinceLastCheckpoint;
 
-    public CheckpointContext(UniqueId actorId, int numTasksSinceLastCheckpoint,
+    public CheckpointContext(ActorId actorId, int numTasksSinceLastCheckpoint,
-        long timeElapsedMsSinceLastCheckpoint) {
+                             long timeElapsedMsSinceLastCheckpoint) {
       this.actorId = actorId;
       this.numTasksSinceLastCheckpoint = numTasksSinceLastCheckpoint;
       this.timeElapsedMsSinceLastCheckpoint = timeElapsedMsSinceLastCheckpoint;
@@ -67,7 +69,7 @@ public interface Checkpointable {
    * @param checkpointId An ID that represents this actor's current state in GCS. You should
    *     save this checkpoint ID together with actor's checkpoint data.
    */
-  void saveCheckpoint(UniqueId actorId, UniqueId checkpointId);
+  void saveCheckpoint(ActorId actorId, UniqueId checkpointId);
 
   /**
    * Load actor's previous checkpoint, and restore actor's state.
@@ -83,7 +85,7 @@ public interface Checkpointable {
    * @return The ID of the checkpoint from which the actor was resumed, or null if the actor should
    *     restart from the beginning.
    */
-  UniqueId loadCheckpoint(UniqueId actorId, List<Checkpoint> availableCheckpoints);
+  UniqueId loadCheckpoint(ActorId actorId, List<Checkpoint> availableCheckpoints);
 
   /**
    * Delete an expired checkpoint;
@@ -95,5 +97,5 @@ public interface Checkpointable {
    * @param actorId ID of the actor.
    * @param checkpointId ID of the checkpoint that has expired.
    */
-  void checkpointExpired(UniqueId actorId, UniqueId checkpointId);
+  void checkpointExpired(ActorId actorId, UniqueId checkpointId);
 }

java/api/src/main/java/org/ray/api/ObjectType.java

@@ -0,0 +1,6 @@
+package org.ray.api;
+
+public enum ObjectType {
+  PUT_OBJECT,
+  RETURN_OBJECT,
+}

java/api/src/main/java/org/ray/api/RayActor.java

@@ -1,5 +1,6 @@
 package org.ray.api;
 
+import org.ray.api.id.ActorId;
 import org.ray.api.id.UniqueId;
 
 /**
@@ -12,7 +13,7 @@ public interface RayActor<T> {
   /**
    * @return The id of this actor.
    */
-  UniqueId getId();
+  ActorId getId();
 
   /**
    * @return The id of this actor handle.

java/api/src/main/java/org/ray/api/id/ActorId.java

@@ -0,0 +1,54 @@
+package org.ray.api.id;
+
+import java.io.Serializable;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.util.Arrays;
+import java.util.Random;
+
+public class ActorId extends BaseId implements Serializable {
+  private static final int UNIQUE_BYTES_LENGTH = 4;
+
+  public static final int LENGTH = UNIQUE_BYTES_LENGTH + JobId.LENGTH;
+
+  public static final ActorId NIL = nil();
+
+  private ActorId(byte[] id) {
+    super(id);
+  }
+
+  public static ActorId fromByteBuffer(ByteBuffer bb) {
+    return new ActorId(byteBuffer2Bytes(bb));
+  }
+
+  public static ActorId fromBytes(byte[] bytes) {
+    return new ActorId(bytes);
+  }
+
+  public static ActorId generateActorId(JobId jobId) {
+    byte[] uniqueBytes = new byte[ActorId.UNIQUE_BYTES_LENGTH];
+    new Random().nextBytes(uniqueBytes);
+
+    byte[] bytes = new byte[ActorId.LENGTH];
+    ByteBuffer wbb = ByteBuffer.wrap(bytes);
+    wbb.order(ByteOrder.LITTLE_ENDIAN);
+
+    System.arraycopy(uniqueBytes, 0, bytes, 0, ActorId.UNIQUE_BYTES_LENGTH);
+    System.arraycopy(jobId.getBytes(), 0, bytes, ActorId.UNIQUE_BYTES_LENGTH, JobId.LENGTH);
+    return new ActorId(bytes);
+  }
+
+  /**
+   * Generate a nil ActorId.
+   */
+  private static ActorId nil() {
+    byte[] b = new byte[LENGTH];
+    Arrays.fill(b, (byte) 0xFF);
+    return new ActorId(b);
+  }
+
+  @Override
+  public int size() {
+    return LENGTH;
+  }
+}

java/api/src/main/java/org/ray/api/id/BaseId.java

@@ -14,7 +14,7 @@ public abstract class BaseId implements Serializable {
   /**
    * Create a BaseId instance according to the input byte array.
    */
-  public BaseId(byte[] id) {
+  protected BaseId(byte[] id) {
     if (id.length != size()) {
       throw new IllegalArgumentException("Failed to construct BaseId, expect " + size()
               + " bytes, but got " + id.length + " bytes.");

java/api/src/main/java/org/ray/api/id/ObjectId.java

@@ -2,8 +2,10 @@ package org.ray.api.id;
 
 import java.io.Serializable;
 import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
 import java.util.Arrays;
 import java.util.Random;
+import org.ray.api.ObjectType;
 
 /**
  * Represents the id of a Ray object.
@@ -11,14 +13,22 @@ import java.util.Random;
 public class ObjectId extends BaseId implements Serializable {
 
   public static final int LENGTH = 20;
+
   public static final ObjectId NIL = genNil();
 
-  /**
+  private static int CREATED_BY_TASK_FLAG_BITS_OFFSET = 15;
-   * Create an ObjectId from a hex string.
+
-   */
+  private static int OBJECT_TYPE_FLAG_BITS_OFFSET = 14;
-  public static ObjectId fromHexString(String hex) {
+
-    return new ObjectId(hexString2Bytes(hex));
+  private static int TRANSPORT_TYPE_FLAG_BITS_OFFSET = 11;
-  }
+
+  private static int FLAGS_BYTES_POS = TaskId.LENGTH;
+
+  private static int FLAGS_BYTES_LENGTH = 2;
+
+  private static int INDEX_BYTES_POS = FLAGS_BYTES_POS + FLAGS_BYTES_LENGTH;
+
+  private static int INDEX_BYTES_LENGTH = 4;
 
   /**
    * Create an ObjectId from a ByteBuffer.
@@ -39,12 +49,54 @@ public class ObjectId extends BaseId implements Serializable {
   /**
    * Generate an ObjectId with random value.
    */
-  public static ObjectId randomId() {
+  public static ObjectId fromRandom() {
     byte[] b = new byte[LENGTH];
     new Random().nextBytes(b);
     return new ObjectId(b);
   }
 
+  /**
+   * Compute the object ID of an object put by the task.
+   */
+  public static ObjectId forPut(TaskId taskId, int putIndex) {
+    short flags = 0;
+    flags = setCreatedByTaskFlag(flags, true);
+    // Set a default transport type with value 0.
+    flags = (short) (flags | (0x0 << TRANSPORT_TYPE_FLAG_BITS_OFFSET));
+    flags = setObjectTypeFlag(flags, ObjectType.PUT_OBJECT);
+
+    byte[] bytes = new byte[ObjectId.LENGTH];
+    System.arraycopy(taskId.getBytes(), 0, bytes, 0, TaskId.LENGTH);
+
+    ByteBuffer wbb = ByteBuffer.wrap(bytes);
+    wbb.order(ByteOrder.LITTLE_ENDIAN);
+    wbb.putShort(FLAGS_BYTES_POS, flags);
+
+    wbb.putInt(INDEX_BYTES_POS, putIndex);
+    return new ObjectId(bytes);
+  }
+
+  /**
+   * Compute the object ID of an object return by the task.
+   */
+  public static ObjectId forReturn(TaskId taskId, int returnIndex) {
+    short flags = 0;
+    flags = setCreatedByTaskFlag(flags, true);
+    // Set a default transport type with value 0.
+    flags = (short) (flags | (0x0 << TRANSPORT_TYPE_FLAG_BITS_OFFSET));
+    flags = setObjectTypeFlag(flags, ObjectType.RETURN_OBJECT);
+
+    byte[] bytes = new byte[ObjectId.LENGTH];
+    System.arraycopy(taskId.getBytes(), 0, bytes, 0, TaskId.LENGTH);
+
+    ByteBuffer wbb = ByteBuffer.wrap(bytes);
+    wbb.order(ByteOrder.LITTLE_ENDIAN);
+    wbb.putShort(FLAGS_BYTES_POS, flags);
+
+    wbb.putInt(INDEX_BYTES_POS, returnIndex);
+    return new ObjectId(bytes);
+  }
+
   public ObjectId(byte[] id) {
     super(id);
   }
@@ -56,7 +108,23 @@ public class ObjectId extends BaseId implements Serializable {
 
   public TaskId getTaskId() {
     byte[] taskIdBytes = Arrays.copyOf(getBytes(), TaskId.LENGTH);
-    return new TaskId(taskIdBytes);
+    return TaskId.fromBytes(taskIdBytes);
+  }
+
+  private static short setCreatedByTaskFlag(short flags, boolean createdByTask) {
+    if (createdByTask) {
+      return (short) (flags | (0x1 << CREATED_BY_TASK_FLAG_BITS_OFFSET));
+    } else {
+      return (short) (flags | (0x0 << CREATED_BY_TASK_FLAG_BITS_OFFSET));
+    }
+  }
+
+  private static short setObjectTypeFlag(short flags, ObjectType objectType) {
+    if (objectType == ObjectType.RETURN_OBJECT) {
+      return (short)(flags | (0x1 << OBJECT_TYPE_FLAG_BITS_OFFSET));
+    } else {
+      return (short)(flags | (0x0 << OBJECT_TYPE_FLAG_BITS_OFFSET));
+    }
   }
 
 }

java/api/src/main/java/org/ray/api/id/TaskId.java

@@ -2,6 +2,7 @@ package org.ray.api.id;
 
 import java.io.Serializable;
 import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
 import java.util.Arrays;
 import java.util.Random;
 
@@ -10,7 +11,10 @@ import java.util.Random;
  */
 public class TaskId extends BaseId implements Serializable {
 
-  public static final int LENGTH = 16;
+  private static final int UNIQUE_BYTES_LENGTH = 6;
+
+  public static final int LENGTH = UNIQUE_BYTES_LENGTH + ActorId.LENGTH;
+
   public static final TaskId NIL = genNil();
 
   /**
@@ -27,6 +31,22 @@ public class TaskId extends BaseId implements Serializable {
     return new TaskId(byteBuffer2Bytes(bb));
   }
 
+  /**
+   * Creates a TaskId from given bytes.
+   */
+  public static TaskId fromBytes(byte[] bytes) {
+    return new TaskId(bytes);
+  }
+
+  /**
+   * Get the id of the actor to which this task belongs
+   */
+  public ActorId getActorId() {
+    byte[] actorIdBytes = new byte[ActorId.LENGTH];
+    System.arraycopy(getBytes(), UNIQUE_BYTES_LENGTH, actorIdBytes, 0, ActorId.LENGTH);
+    return ActorId.fromByteBuffer(ByteBuffer.wrap(actorIdBytes));
+  }
+
   /**
    * Generate a nil TaskId.
    */
@@ -36,16 +56,7 @@ public class TaskId extends BaseId implements Serializable {
     return new TaskId(b);
   }
 
-  /**
+  private TaskId(byte[] id) {
-   * Generate an TaskId with random value.
-   */
-  public static TaskId randomId() {
-    byte[] b = new byte[LENGTH];
-    new Random().nextBytes(b);
-    return new TaskId(b);
-  }
-
-  public TaskId(byte[] id) {
     super(id);
   }
 

java/api/src/main/java/org/ray/api/runtimecontext/RuntimeContext.java

@@ -1,8 +1,8 @@
 package org.ray.api.runtimecontext;
 
 import java.util.List;
+import org.ray.api.id.ActorId;
 import org.ray.api.id.JobId;
-import org.ray.api.id.UniqueId;
 
 /**
  * A class used for getting information of Ray runtime.
@@ -19,7 +19,7 @@ public interface RuntimeContext {
    *
    * Note, this can only be called in actors.
    */
-  UniqueId getCurrentActorId();
+  ActorId getCurrentActorId();
 
   /**
    * Returns true if the current actor was reconstructed, false if it's created for the first time.

java/runtime/src/main/java/org/ray/runtime/AbstractRayRuntime.java

@@ -19,6 +19,8 @@ import org.ray.api.RayPyActor;
 import org.ray.api.WaitResult;
 import org.ray.api.exception.RayException;
 import org.ray.api.function.RayFunc;
+import org.ray.api.id.ActorId;
+import org.ray.api.id.JobId;
 import org.ray.api.id.ObjectId;
 import org.ray.api.id.TaskId;
 import org.ray.api.id.UniqueId;
@@ -34,10 +36,10 @@ import org.ray.runtime.functionmanager.PyFunctionDescriptor;
 import org.ray.runtime.gcs.GcsClient;
 import org.ray.runtime.objectstore.ObjectStoreProxy;
 import org.ray.runtime.raylet.RayletClient;
+import org.ray.runtime.raylet.RayletClientImpl;
 import org.ray.runtime.task.ArgumentsBuilder;
 import org.ray.runtime.task.TaskLanguage;
 import org.ray.runtime.task.TaskSpec;
-import org.ray.runtime.util.IdUtil;
 import org.ray.runtime.util.StringUtil;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -123,9 +125,8 @@ public abstract class AbstractRayRuntime implements RayRuntime {
 
   @Override
   public <T> RayObject<T> put(T obj) {
-    ObjectId objectId = IdUtil.computePutId(
+    ObjectId objectId = ObjectId.forPut(workerContext.getCurrentTaskId(),
-        workerContext.getCurrentTaskId(), workerContext.nextPutIndex());
+        workerContext.nextPutIndex());
-
     put(objectId, obj);
     return new RayObjectImpl<>(objectId);
   }
@@ -144,8 +145,8 @@ public abstract class AbstractRayRuntime implements RayRuntime {
    * @return A RayObject instance that represents the in-store object.
    */
   public RayObject<Object> putSerialized(byte[] obj) {
-    ObjectId objectId = IdUtil.computePutId(
+    ObjectId objectId = ObjectId.forPut(workerContext.getCurrentTaskId(),
-        workerContext.getCurrentTaskId(), workerContext.nextPutIndex());
+        workerContext.nextPutIndex());
     TaskId taskId = workerContext.getCurrentTaskId();
     LOGGER.debug("Putting serialized object {}, for task {} ", objectId, taskId);
     objectStoreProxy.putSerialized(objectId, obj);
@@ -212,7 +213,7 @@ public abstract class AbstractRayRuntime implements RayRuntime {
       Object[] args, ActorCreationOptions options) {
     TaskSpec spec = createTaskSpec(actorFactoryFunc, null, RayActorImpl.NIL,
         args, true, false, options);
-    RayActorImpl<?> actor = new RayActorImpl(new UniqueId(spec.returnIds[0].getBytes()));
+    RayActorImpl<?> actor = new RayActorImpl(spec.taskId.getActorId());
     actor.increaseTaskCounter();
     actor.setTaskCursor(spec.returnIds[0]);
     rayletClient.submitTask(spec);
@@ -272,7 +273,7 @@ public abstract class AbstractRayRuntime implements RayRuntime {
    *
    * @param func The target remote function.
    * @param pyFunctionDescriptor Descriptor of the target Python function, if the task is a Python
-   * task.
+   *                             task.
    * @param actor The actor handle. If the task is not an actor task, actor id must be NIL.
    * @param args The arguments for the remote function.
    * @param isActorCreationTask Whether this task is an actor creation task.
@@ -284,16 +285,22 @@ public abstract class AbstractRayRuntime implements RayRuntime {
       boolean isActorCreationTask, boolean isActorTask, BaseTaskOptions taskOptions) {
     Preconditions.checkArgument((func == null) != (pyFunctionDescriptor == null));
 
-    TaskId taskId = rayletClient.generateTaskId(workerContext.getCurrentJobId(),
+    ActorId actorCreationId = ActorId.NIL;
-        workerContext.getCurrentTaskId(), workerContext.nextTaskIndex());
+    TaskId taskId = null;
-    int numReturns = actor.getId().isNil() ? 1 : 2;
+    final JobId currentJobId = workerContext.getCurrentJobId();
-    ObjectId[] returnIds = IdUtil.genReturnIds(taskId, numReturns);
+    final TaskId currentTaskId = workerContext.getCurrentTaskId();
-
+    final int taskIndex = workerContext.nextTaskIndex();
-    UniqueId actorCreationId = UniqueId.NIL;
     if (isActorCreationTask) {
-      actorCreationId = new UniqueId(returnIds[0].getBytes());
+      taskId = RayletClientImpl.generateActorCreationTaskId(currentJobId, currentTaskId, taskIndex);
+      actorCreationId = taskId.getActorId();
+    } else if (isActorTask) {
+      taskId = RayletClientImpl.generateActorTaskId(currentJobId, currentTaskId, taskIndex, actor.getId());
+    } else {
+      taskId = RayletClientImpl.generateNormalTaskId(currentJobId, currentTaskId, taskIndex);
     }
 
+    int numReturns = actor.getId().isNil() ? 1 : 2;
+
     Map<String, Double> resources;
     if (null == taskOptions) {
       resources = new HashMap<>();
@@ -337,7 +344,7 @@ public abstract class AbstractRayRuntime implements RayRuntime {
         actor.getId(),
         actor.getHandleId(),
         actor.increaseTaskCounter(),
-	previousActorTaskDummyObjectId,
+        previousActorTaskDummyObjectId,
         actor.getNewActorHandles().toArray(new UniqueId[0]),
         ArgumentsBuilder.wrap(args, language == TaskLanguage.PYTHON),
         numReturns,

java/runtime/src/main/java/org/ray/runtime/RayActorImpl.java

@@ -7,6 +7,7 @@ import java.io.ObjectOutput;
 import java.util.ArrayList;
 import java.util.List;
 import org.ray.api.RayActor;
+import org.ray.api.id.ActorId;
 import org.ray.api.id.ObjectId;
 import org.ray.api.id.UniqueId;
 import org.ray.runtime.util.Sha1Digestor;
@@ -18,7 +19,7 @@ public class RayActorImpl<T> implements RayActor<T>, Externalizable {
   /**
    * Id of this actor.
    */
-  protected UniqueId id;
+  protected ActorId id;
   /**
    * Handle id of this actor.
    */
@@ -47,14 +48,14 @@ public class RayActorImpl<T> implements RayActor<T>, Externalizable {
   protected List<UniqueId> newActorHandles;
 
   public RayActorImpl() {
-    this(UniqueId.NIL, UniqueId.NIL);
+    this(ActorId.NIL, UniqueId.NIL);
   }
 
-  public RayActorImpl(UniqueId id) {
+  public RayActorImpl(ActorId id) {
     this(id, UniqueId.NIL);
   }
 
-  public RayActorImpl(UniqueId id, UniqueId handleId) {
+  public RayActorImpl(ActorId id, UniqueId handleId) {
     this.id = id;
     this.handleId = handleId;
     this.taskCounter = 0;
@@ -64,7 +65,7 @@ public class RayActorImpl<T> implements RayActor<T>, Externalizable {
   }
 
   @Override
-  public UniqueId getId() {
+  public ActorId getId() {
     return id;
   }
 
@@ -120,7 +121,7 @@ public class RayActorImpl<T> implements RayActor<T>, Externalizable {
 
   @Override
   public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
-    this.id = (UniqueId) in.readObject();
+    this.id = (ActorId) in.readObject();
     this.handleId = (UniqueId) in.readObject();
     this.taskCursor = (ObjectId) in.readObject();
     this.taskCounter = (int) in.readObject();

java/runtime/src/main/java/org/ray/runtime/RayPyActorImpl.java

@@ -4,11 +4,11 @@ import java.io.IOException;
 import java.io.ObjectInput;
 import java.io.ObjectOutput;
 import org.ray.api.RayPyActor;
-import org.ray.api.id.UniqueId;
+import org.ray.api.id.ActorId;
 
 public class RayPyActorImpl extends RayActorImpl implements RayPyActor {
 
-  public static final RayPyActorImpl NIL = new RayPyActorImpl(UniqueId.NIL, null, null);
+  public static final RayPyActorImpl NIL = new RayPyActorImpl(ActorId.NIL, null, null);
 
   /**
    * Module name of the Python actor class.
@@ -24,7 +24,7 @@ public class RayPyActorImpl extends RayActorImpl implements RayPyActor {
   // since it'll be needed when deserializing.
   public RayPyActorImpl() {}
 
-  public RayPyActorImpl(UniqueId id, String moduleName, String className) {
+  public RayPyActorImpl(ActorId id, String moduleName, String className) {
     super(id);
     this.moduleName = moduleName;
     this.className = className;

java/runtime/src/main/java/org/ray/runtime/RuntimeContextImpl.java

@@ -2,8 +2,9 @@ package org.ray.runtime;
 
 import com.google.common.base.Preconditions;
 import java.util.List;
+
+import org.ray.api.id.ActorId;
 import org.ray.api.id.JobId;
-import org.ray.api.id.UniqueId;
 import org.ray.api.runtimecontext.NodeInfo;
 import org.ray.api.runtimecontext.RuntimeContext;
 import org.ray.runtime.config.RunMode;
@@ -23,7 +24,7 @@ public class RuntimeContextImpl implements RuntimeContext {
   }
 
   @Override
-  public UniqueId getCurrentActorId() {
+  public ActorId getCurrentActorId() {
     Worker worker = runtime.getWorker();
     Preconditions.checkState(worker != null && !worker.getCurrentActorId().isNil(),
         "This method should only be called from an actor.");

java/runtime/src/main/java/org/ray/runtime/Worker.java

@@ -7,12 +7,14 @@ import org.ray.api.Checkpointable;
 import org.ray.api.Checkpointable.Checkpoint;
 import org.ray.api.Checkpointable.CheckpointContext;
 import org.ray.api.exception.RayTaskException;
+import org.ray.api.id.ActorId;
 import org.ray.api.id.ObjectId;
 import org.ray.api.id.UniqueId;
 import org.ray.runtime.config.RunMode;
 import org.ray.runtime.functionmanager.RayFunction;
 import org.ray.runtime.task.ArgumentsBuilder;
 import org.ray.runtime.task.TaskSpec;
+import org.ray.runtime.util.IdUtil;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -37,7 +39,7 @@ public class Worker {
   /**
    * Id of the current actor object, if the worker is an actor, otherwise NIL.
    */
-  private UniqueId currentActorId = UniqueId.NIL;
+  private ActorId currentActorId = ActorId.NIL;
 
   /**
    * The exception that failed the actor creation task, if any.
@@ -64,7 +66,7 @@ public class Worker {
     this.runtime = runtime;
   }
 
-  public UniqueId getCurrentActorId() {
+  public ActorId getCurrentActorId() {
     return currentActorId;
   }
 
@@ -92,7 +94,7 @@ public class Worker {
       Thread.currentThread().setContextClassLoader(rayFunction.classLoader);
 
       if (spec.isActorCreationTask()) {
-        currentActorId = new UniqueId(returnId.getBytes());
+        currentActorId = spec.taskId.getActorId();
       }
 
       // Get local actor object and arguments.
@@ -118,9 +120,10 @@ public class Worker {
         if (spec.isActorTask()) {
           maybeSaveCheckpoint(actor, spec.actorId);
         }
+
         runtime.put(returnId, result);
       } else {
-        maybeLoadCheckpoint(result, new UniqueId(returnId.getBytes()));
+        maybeLoadCheckpoint(result, spec.taskId.getActorId());
         currentActor = result;
       }
       LOGGER.debug("Finished executing task {}", spec.taskId);
@@ -136,7 +139,7 @@ public class Worker {
     }
   }
 
-  private void maybeSaveCheckpoint(Object actor, UniqueId actorId) {
+  private void maybeSaveCheckpoint(Object actor, ActorId actorId) {
     if (!(actor instanceof Checkpointable)) {
       return;
     }
@@ -161,7 +164,7 @@ public class Worker {
     checkpointable.saveCheckpoint(actorId, checkpointId);
   }
 
-  private void maybeLoadCheckpoint(Object actor, UniqueId actorId) {
+  private void maybeLoadCheckpoint(Object actor, ActorId actorId) {
     if (!(actor instanceof Checkpointable)) {
       return;
     }

java/runtime/src/main/java/org/ray/runtime/WorkerContext.java

@@ -48,7 +48,7 @@ public class WorkerContext {
    * for other threads, this method returns a random ID.
    */
   public TaskId getCurrentTaskId() {
-    return new TaskId(nativeGetCurrentTaskId(nativeWorkerContextPointer));
+    return TaskId.fromBytes(nativeGetCurrentTaskId(nativeWorkerContextPointer));
   }
 
   /**

java/runtime/src/main/java/org/ray/runtime/gcs/GcsClient.java

@@ -9,6 +9,7 @@ import java.util.Map;
 import java.util.stream.Collectors;
 import org.apache.commons.lang3.ArrayUtils;
 import org.ray.api.Checkpointable.Checkpoint;
+import org.ray.api.id.ActorId;
 import org.ray.api.id.BaseId;
 import org.ray.api.id.JobId;
 import org.ray.api.id.TaskId;
@@ -117,7 +118,7 @@ public class GcsClient {
   /**
    * If the actor exists in GCS.
    */
-  public boolean actorExists(UniqueId actorId) {
+  public boolean actorExists(ActorId actorId) {
     byte[] key = ArrayUtils.addAll(
         TablePrefix.ACTOR.toString().getBytes(), actorId.getBytes());
     return primary.exists(key);
@@ -136,7 +137,7 @@ public class GcsClient {
   /**
    * Get the available checkpoints for the given actor ID.
    */
-  public List<Checkpoint> getCheckpointsForActor(UniqueId actorId) {
+  public List<Checkpoint> getCheckpointsForActor(ActorId actorId) {
     List<Checkpoint> checkpoints = new ArrayList<>();
     final String prefix = TablePrefix.ACTOR_CHECKPOINT_ID.toString();
     final byte[] key = ArrayUtils.addAll(prefix.getBytes(), actorId.getBytes());

java/runtime/src/main/java/org/ray/runtime/objectstore/MockObjectInterface.java

@@ -9,7 +9,6 @@ import java.util.function.Consumer;
 import java.util.stream.Collectors;
 import org.ray.api.id.ObjectId;
 import org.ray.runtime.WorkerContext;
-import org.ray.runtime.util.IdUtil;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -37,7 +36,7 @@ public class MockObjectInterface implements ObjectInterface {
 
   @Override
   public ObjectId put(NativeRayObject obj) {
-    ObjectId objectId = IdUtil.computePutId(workerContext.getCurrentTaskId(),
+    ObjectId objectId = ObjectId.forPut(workerContext.getCurrentTaskId(),
         workerContext.nextPutIndex());
     put(obj, objectId);
     return objectId;

java/runtime/src/main/java/org/ray/runtime/objectstore/ObjectInterfaceImpl.java

@@ -57,7 +57,8 @@ public class ObjectInterfaceImpl implements ObjectInterface {
 
   @Override
   public void delete(List<ObjectId> objectIds, boolean localOnly, boolean deleteCreatingTasks) {
-    nativeDelete(nativeObjectInterfacePointer, toBinaryList(objectIds), localOnly, deleteCreatingTasks);
+    nativeDelete(nativeObjectInterfacePointer,
+        toBinaryList(objectIds), localOnly, deleteCreatingTasks);
   }
 
   public void destroy() {

java/runtime/src/main/java/org/ray/runtime/raylet/MockRayletClient.java

@@ -18,7 +18,7 @@ import java.util.stream.Collectors;
 import org.apache.commons.lang3.NotImplementedException;
 import org.ray.api.RayObject;
 import org.ray.api.WaitResult;
-import org.ray.api.id.JobId;
+import org.ray.api.id.ActorId;
 import org.ray.api.id.ObjectId;
 import org.ray.api.id.TaskId;
 import org.ray.api.id.UniqueId;
@@ -43,7 +43,7 @@ public class MockRayletClient implements RayletClient {
   private final RayDevRuntime runtime;
   private final ExecutorService exec;
   private final Deque<Worker> idleWorkers;
-  private final Map<UniqueId, Worker> actorWorkers;
+  private final Map<ActorId, Worker> actorWorkers;
   private final ThreadLocal<Worker> currentWorker;
 
   public MockRayletClient(RayDevRuntime runtime, int numberThreads) {
@@ -154,11 +154,6 @@ public class MockRayletClient implements RayletClient {
     throw new RuntimeException("invalid execution flow here");
   }
 
-  @Override
-  public TaskId generateTaskId(JobId jobId, TaskId parentTaskId, int taskIndex) {
-    return TaskId.randomId();
-  }
-
   @Override
   public <T> WaitResult<T> wait(List<RayObject<T>> waitFor, int numReturns, int
       timeoutMs, TaskId currentTaskId) {
@@ -188,12 +183,12 @@ public class MockRayletClient implements RayletClient {
 
 
   @Override
-  public UniqueId prepareCheckpoint(UniqueId actorId) {
+  public UniqueId prepareCheckpoint(ActorId actorId) {
     throw new NotImplementedException("Not implemented.");
   }
 
   @Override
-  public void notifyActorResumedFromCheckpoint(UniqueId actorId, UniqueId checkpointId) {
+  public void notifyActorResumedFromCheckpoint(ActorId actorId, UniqueId checkpointId) {
     throw new NotImplementedException("Not implemented.");
   }
 

java/runtime/src/main/java/org/ray/runtime/raylet/RayletClient.java

@@ -3,7 +3,7 @@ package org.ray.runtime.raylet;
 import java.util.List;
 import org.ray.api.RayObject;
 import org.ray.api.WaitResult;
-import org.ray.api.id.JobId;
+import org.ray.api.id.ActorId;
 import org.ray.api.id.ObjectId;
 import org.ray.api.id.TaskId;
 import org.ray.api.id.UniqueId;
@@ -18,16 +18,14 @@ public interface RayletClient {
 
   TaskSpec getTask();
 
-  TaskId generateTaskId(JobId jobId, TaskId parentTaskId, int taskIndex);
-
   <T> WaitResult<T> wait(List<RayObject<T>> waitFor, int numReturns, int
       timeoutMs, TaskId currentTaskId);
 
   void freePlasmaObjects(List<ObjectId> objectIds, boolean localOnly, boolean deleteCreatingTasks);
 
-  UniqueId prepareCheckpoint(UniqueId actorId);
+  UniqueId prepareCheckpoint(ActorId actorId);
 
-  void notifyActorResumedFromCheckpoint(UniqueId actorId, UniqueId checkpointId);
+  void notifyActorResumedFromCheckpoint(ActorId actorId, UniqueId checkpointId);
 
   void setResource(String resourceName, double capacity, UniqueId nodeId);
 

java/runtime/src/main/java/org/ray/runtime/raylet/RayletClientImpl.java

@@ -4,6 +4,7 @@ import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
 import com.google.protobuf.ByteString;
 import com.google.protobuf.InvalidProtocolBufferException;
+import java.nio.ByteBuffer;
 import java.nio.charset.Charset;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -13,10 +14,11 @@ import java.util.stream.Collectors;
 import org.ray.api.RayObject;
 import org.ray.api.WaitResult;
 import org.ray.api.exception.RayException;
-import org.ray.api.id.JobId;
+import org.ray.api.id.ActorId;
-import org.ray.api.id.ObjectId;
-import org.ray.api.id.TaskId;
 import org.ray.api.id.UniqueId;
+import org.ray.api.id.JobId;
+import org.ray.api.id.TaskId;
+import org.ray.api.id.ObjectId;
 import org.ray.runtime.functionmanager.JavaFunctionDescriptor;
 import org.ray.runtime.generated.Common;
 import org.ray.runtime.generated.Common.TaskType;
@@ -93,12 +95,6 @@ public class RayletClientImpl implements RayletClient {
     return parseTaskSpecFromProtobuf(bytes);
   }
 
-  @Override
-  public TaskId generateTaskId(JobId jobId, TaskId parentTaskId, int taskIndex) {
-    byte[] bytes = nativeGenerateTaskId(jobId.getBytes(), parentTaskId.getBytes(), taskIndex);
-    return new TaskId(bytes);
-  }
-
   @Override
   public void freePlasmaObjects(List<ObjectId> objectIds, boolean localOnly,
       boolean deleteCreatingTasks) {
@@ -107,15 +103,30 @@ public class RayletClientImpl implements RayletClient {
   }
 
   @Override
-  public UniqueId prepareCheckpoint(UniqueId actorId) {
+  public UniqueId prepareCheckpoint(ActorId actorId) {
     return new UniqueId(nativePrepareCheckpoint(client, actorId.getBytes()));
   }
 
   @Override
-  public void notifyActorResumedFromCheckpoint(UniqueId actorId, UniqueId checkpointId) {
+  public void notifyActorResumedFromCheckpoint(ActorId actorId, UniqueId checkpointId) {
     nativeNotifyActorResumedFromCheckpoint(client, actorId.getBytes(), checkpointId.getBytes());
   }
 
+  public static TaskId generateActorCreationTaskId(JobId jobId, TaskId parentTaskId, int taskIndex) {
+    byte[] bytes = nativeGenerateActorCreationTaskId(jobId.getBytes(), parentTaskId.getBytes(), taskIndex);
+    return TaskId.fromBytes(bytes);
+  }
+
+  public static TaskId generateActorTaskId(JobId jobId, TaskId parentTaskId, int taskIndex, ActorId actorId) {
+    byte[] bytes = nativeGenerateActorTaskId(jobId.getBytes(), parentTaskId.getBytes(), taskIndex, actorId.getBytes());
+    return TaskId.fromBytes(bytes);
+  }
+
+  public static TaskId generateNormalTaskId(JobId jobId, TaskId parentTaskId, int taskIndex) {
+    byte[] bytes = nativeGenerateNormalTaskId(jobId.getBytes(), parentTaskId.getBytes(), taskIndex);
+    return TaskId.fromBytes(bytes);
+  }
+
   /**
    * Parse `TaskSpec` protobuf bytes.
    */
@@ -160,13 +171,13 @@ public class RayletClientImpl implements RayletClient {
     );
 
     // Parse ActorCreationTaskSpec.
-    UniqueId actorCreationId = UniqueId.NIL;
+    ActorId actorCreationId = ActorId.NIL;
     int maxActorReconstructions = 0;
     UniqueId[] newActorHandles = new UniqueId[0];
     List<String> dynamicWorkerOptions = new ArrayList<>();
     if (taskSpec.getType() == Common.TaskType.ACTOR_CREATION_TASK) {
       Common.ActorCreationTaskSpec actorCreationTaskSpec = taskSpec.getActorCreationTaskSpec();
-      actorCreationId = UniqueId
+      actorCreationId = ActorId
           .fromByteBuffer(actorCreationTaskSpec.getActorId().asReadOnlyByteBuffer());
       maxActorReconstructions = (int) actorCreationTaskSpec.getMaxActorReconstructions();
       dynamicWorkerOptions = ImmutableList
@@ -174,18 +185,18 @@ public class RayletClientImpl implements RayletClient {
     }
 
     // Parse ActorTaskSpec.
-    UniqueId actorId = UniqueId.NIL;
+    ActorId actorId = ActorId.NIL;
     UniqueId actorHandleId = UniqueId.NIL;
     ObjectId previousActorTaskDummyObjectId = ObjectId.NIL;
     int actorCounter = 0;
     if (taskSpec.getType() == Common.TaskType.ACTOR_TASK) {
       Common.ActorTaskSpec actorTaskSpec = taskSpec.getActorTaskSpec();
-      actorId = UniqueId.fromByteBuffer(actorTaskSpec.getActorId().asReadOnlyByteBuffer());
+      actorId = ActorId.fromByteBuffer(actorTaskSpec.getActorId().asReadOnlyByteBuffer());
       actorHandleId = UniqueId
           .fromByteBuffer(actorTaskSpec.getActorHandleId().asReadOnlyByteBuffer());
       actorCounter = (int) actorTaskSpec.getActorCounter();
       previousActorTaskDummyObjectId = ObjectId.fromByteBuffer(
-		      actorTaskSpec.getPreviousActorTaskDummyObjectId().asReadOnlyByteBuffer());
+          actorTaskSpec.getPreviousActorTaskDummyObjectId().asReadOnlyByteBuffer());
       newActorHandles = actorTaskSpec.getNewActorHandlesList().stream()
           .map(byteString -> UniqueId.fromByteBuffer(byteString.asReadOnlyByteBuffer()))
           .toArray(UniqueId[]::new);
@@ -193,8 +204,8 @@ public class RayletClientImpl implements RayletClient {
 
     return new TaskSpec(jobId, taskId, parentTaskId, parentCounter, actorCreationId,
         maxActorReconstructions, actorId, actorHandleId, actorCounter,
-	previousActorTaskDummyObjectId, newActorHandles, args, numReturns, resources,
+        previousActorTaskDummyObjectId, newActorHandles, args, numReturns, resources,
-	TaskLanguage.JAVA, functionDescriptor, dynamicWorkerOptions);
+        TaskLanguage.JAVA, functionDescriptor, dynamicWorkerOptions);
   }
 
   /**
@@ -255,13 +266,16 @@ public class RayletClientImpl implements RayletClient {
       builder.setType(TaskType.ACTOR_TASK);
       List<ByteString> newHandles = Arrays.stream(task.newActorHandles)
           .map(id -> ByteString.copyFrom(id.getBytes())).collect(Collectors.toList());
+      final ObjectId actorCreationDummyObjectId = IdUtil.computeActorCreationDummyObjectId(
+          ActorId.fromByteBuffer(ByteBuffer.wrap(task.actorId.getBytes())));
       builder.setActorTaskSpec(
           Common.ActorTaskSpec.newBuilder()
               .setActorId(ByteString.copyFrom(task.actorId.getBytes()))
               .setActorHandleId(ByteString.copyFrom(task.actorHandleId.getBytes()))
-              .setActorCreationDummyObjectId(ByteString.copyFrom(task.actorId.getBytes()))
+              .setActorCreationDummyObjectId(
+                  ByteString.copyFrom(actorCreationDummyObjectId.getBytes()))
               .setPreviousActorTaskDummyObjectId(
-		      ByteString.copyFrom(task.previousActorTaskDummyObjectId.getBytes()))
+                  ByteString.copyFrom(task.previousActorTaskDummyObjectId.getBytes()))
               .setActorCounter(task.actorCounter)
               .addAllNewActorHandles(newHandles)
       );
@@ -307,9 +321,6 @@ public class RayletClientImpl implements RayletClient {
   private static native boolean[] nativeWaitObject(long conn, byte[][] objectIds,
       int numReturns, int timeout, boolean waitLocal, byte[] currentTaskId) throws RayException;
 
-  private static native byte[] nativeGenerateTaskId(byte[] jobId, byte[] parentTaskId,
-      int taskIndex);
-
   private static native void nativeFreePlasmaObjects(long conn, byte[][] objectIds,
       boolean localOnly, boolean deleteCreatingTasks) throws RayException;
 
@@ -320,4 +331,13 @@ public class RayletClientImpl implements RayletClient {
 
   private static native void nativeSetResource(long conn, String resourceName, double capacity,
       byte[] nodeId) throws RayException;
+
+  private static native byte[] nativeGenerateActorCreationTaskId(byte[] jobId, byte[] parentTaskId,
+                                                                 int taskIndex);
+
+  private static native byte[] nativeGenerateActorTaskId(byte[] jobId, byte[] parentTaskId,
+                                                          int taskIndex, byte[] actorId);
+
+  private static native byte[] nativeGenerateNormalTaskId(byte[] jobId, byte[] parentTaskId,
+                                                          int taskIndex);
 }

java/runtime/src/main/java/org/ray/runtime/task/TaskSpec.java

@@ -1,18 +1,17 @@
 package org.ray.runtime.task;
 
 import com.google.common.base.Preconditions;
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
+import org.ray.api.id.ActorId;
 import org.ray.api.id.JobId;
-import org.ray.api.id.ObjectId;
 import org.ray.api.id.TaskId;
+import org.ray.api.id.ObjectId;
 import org.ray.api.id.UniqueId;
 import org.ray.runtime.functionmanager.FunctionDescriptor;
 import org.ray.runtime.functionmanager.JavaFunctionDescriptor;
 import org.ray.runtime.functionmanager.PyFunctionDescriptor;
-import org.ray.runtime.util.IdUtil;
 
 /**
  * Represents necessary information of a task for scheduling and executing.
@@ -32,13 +31,13 @@ public class TaskSpec {
   public final int parentCounter;
 
   // Id for createActor a target actor
-  public final UniqueId actorCreationId;
+  public final ActorId actorCreationId;
 
   public final int maxActorReconstructions;
 
   // Actor ID of the task. This is the actor that this task is executed on
   // or NIL_ACTOR_ID if the task is just a normal task.
-  public final UniqueId actorId;
+  public final ActorId actorId;
 
   // ID per actor client for session consistency
   public final UniqueId actorHandleId;
@@ -87,9 +86,9 @@ public class TaskSpec {
       TaskId taskId,
       TaskId parentTaskId,
       int parentCounter,
-      UniqueId actorCreationId,
+      ActorId actorCreationId,
       int maxActorReconstructions,
-      UniqueId actorId,
+      ActorId actorId,
       UniqueId actorHandleId,
       int actorCounter,
       ObjectId previousActorTaskDummyObjectId,
@@ -117,7 +116,7 @@ public class TaskSpec {
 
     returnIds = new ObjectId[numReturns];
     for (int i = 0; i < numReturns; ++i) {
-      returnIds[i] = IdUtil.computeReturnId(taskId, i + 1);
+      returnIds[i] = ObjectId.forReturn(taskId, i + 1);
     }
     this.resources = resources;
     this.language = language;

java/runtime/src/main/java/org/ray/runtime/util/IdUtil.java

@@ -1,15 +1,11 @@
 package org.ray.runtime.util;
 
-import com.google.common.base.Preconditions;
 import java.nio.ByteBuffer;
-import java.nio.ByteOrder;
 import java.util.Arrays;
 import java.util.List;
 import org.ray.api.id.BaseId;
-import org.ray.api.id.JobId;
 import org.ray.api.id.ObjectId;
-import org.ray.api.id.TaskId;
+import org.ray.api.id.ActorId;
-import org.ray.api.id.UniqueId;
 
 /**
  * Helper method for different Ids.
@@ -17,60 +13,6 @@ import org.ray.api.id.UniqueId;
  * in src/ray/common/id.h
  */
 public class IdUtil {
-  public static final int OBJECT_INDEX_POS = 16;
-
-  /**
-   * Compute the object ID of an object returned by the task.
-   *
-   * @param taskId The task ID of the task that created the object.
-   * @param returnIndex What number return value this object is in the task.
-   * @return The computed object ID.
-   */
-  public static ObjectId computeReturnId(TaskId taskId, int returnIndex) {
-    return computeObjectId(taskId, returnIndex);
-  }
-
-  /**
-   * Compute the object ID from the task ID and the index.
-   * @param taskId The task ID of the task that created the object.
-   * @param index The index which can distinguish different objects in one task.
-   * @return The computed object ID.
-   */
-  private static ObjectId computeObjectId(TaskId taskId, int index) {
-    byte[] bytes = new byte[ObjectId.LENGTH];
-    System.arraycopy(taskId.getBytes(), 0, bytes, 0, taskId.size());
-    ByteBuffer wbb = ByteBuffer.wrap(bytes);
-    wbb.order(ByteOrder.LITTLE_ENDIAN);
-    wbb.putInt(OBJECT_INDEX_POS, index);
-    return new ObjectId(bytes);
-  }
-
-  /**
-   * Compute the object ID of an object put by the task.
-   *
-   * @param taskId The task ID of the task that created the object.
-   * @param putIndex What number put this object was created by in the task.
-   * @return The computed object ID.
-   */
-  public static ObjectId computePutId(TaskId taskId, int putIndex) {
-    // We multiply putIndex by -1 to distinguish from returnIndex.
-    return computeObjectId(taskId, -1 * putIndex);
-  }
-
-  /**
-   * Generate the return ids of a task.
-   *
-   * @param taskId The ID of the task that generates returnsIds.
-   * @param numReturns The number of returnIds.
-   * @return The Return Ids of this task.
-   */
-  public static ObjectId[] genReturnIds(TaskId taskId, int numReturns) {
-    ObjectId[] ret = new ObjectId[numReturns];
-    for (int i = 0; i < numReturns; i++) {
-      ret[i] = IdUtil.computeReturnId(taskId, i + 1);
-    }
-    return ret;
-  }
 
   public static <T extends BaseId> byte[][] getIdBytes(List<T> objectIds) {
     int size = objectIds.size();
@@ -81,79 +23,6 @@ public class IdUtil {
     return ids;
   }
 
-  public static byte[][] getByteListFromByteBuffer(ByteBuffer byteBufferOfIds, int length) {
-    Preconditions.checkArgument(byteBufferOfIds != null);
-
-    byte[] bytesOfIds = new byte[byteBufferOfIds.remaining()];
-    byteBufferOfIds.get(bytesOfIds, 0, byteBufferOfIds.remaining());
-
-    int count = bytesOfIds.length / length;
-    byte[][] idBytes = new byte[count][];
-
-    for (int i = 0; i < count; ++i) {
-      byte[] id = new byte[length];
-      System.arraycopy(bytesOfIds, i * length, id, 0, length);
-      idBytes[i] = id;
-    }
-
-    return idBytes;
-  }
-
-  /**
-   * Get unique IDs from concatenated ByteBuffer.
-   *
-   * @param byteBufferOfIds The ByteBuffer concatenated from IDs.
-   * @return The array of unique IDs.
-   */
-  public static UniqueId[] getUniqueIdsFromByteBuffer(ByteBuffer byteBufferOfIds) {
-    byte[][]idBytes = getByteListFromByteBuffer(byteBufferOfIds, UniqueId.LENGTH);
-    UniqueId[] uniqueIds = new UniqueId[idBytes.length];
-
-    for (int i = 0; i < idBytes.length; ++i) {
-      uniqueIds[i] = UniqueId.fromByteBuffer(ByteBuffer.wrap(idBytes[i]));
-    }
-
-    return uniqueIds;
-  }
-
-  /**
-   * Get object IDs from concatenated ByteBuffer.
-   *
-   * @param byteBufferOfIds The ByteBuffer concatenated from IDs.
-   * @return The array of object IDs.
-   */
-  public static ObjectId[] getObjectIdsFromByteBuffer(ByteBuffer byteBufferOfIds) {
-    byte[][]idBytes = getByteListFromByteBuffer(byteBufferOfIds, UniqueId.LENGTH);
-    ObjectId[] objectIds = new ObjectId[idBytes.length];
-
-    for (int i = 0; i < idBytes.length; ++i) {
-      objectIds[i] = ObjectId.fromByteBuffer(ByteBuffer.wrap(idBytes[i]));
-    }
-
-    return objectIds;
-  }
-
-  /**
-   * Concatenate IDs to a ByteBuffer.
-   *
-   * @param ids The array of IDs that will be concatenated.
-   * @return A ByteBuffer that contains bytes of concatenated IDs.
-   */
-  public static <T extends BaseId> ByteBuffer concatIds(T[] ids) {
-    int length = 0;
-    if (ids != null && ids.length != 0) {
-      length = ids[0].size() * ids.length;
-    }
-    byte[] bytesOfIds = new byte[length];
-    for (int i = 0; i < ids.length; ++i) {
-      System.arraycopy(ids[i].getBytes(), 0, bytesOfIds,
-          i * ids[i].size(), ids[i].size());
-    }
-
-    return ByteBuffer.wrap(bytesOfIds);
-  }
-
-
   /**
    * Compute the murmur hash code of this ID.
    */
@@ -221,4 +90,16 @@ public class IdUtil {
 
     return h;
   }
+
+  /*
+   * A helper function to compute actor creation dummy object id according
+   * the given actor id.
+   */
+  public static ObjectId computeActorCreationDummyObjectId(ActorId actorId) {
+    byte[] bytes = new byte[ObjectId.LENGTH];
+    System.arraycopy(actorId.getBytes(), 0, bytes, 0, ActorId.LENGTH);
+    Arrays.fill(bytes, ActorId.LENGTH, bytes.length, (byte) 0xFF);
+    return ObjectId.fromByteBuffer(ByteBuffer.wrap(bytes));
+  }
+
 }

java/test/src/main/java/org/ray/api/test/ActorReconstructionTest.java

@@ -11,6 +11,7 @@ import org.ray.api.RayActor;
 import org.ray.api.TestUtils;
 import org.ray.api.annotation.RayRemote;
 import org.ray.api.exception.RayActorException;
+import org.ray.api.id.ActorId;
 import org.ray.api.id.UniqueId;
 import org.ray.api.options.ActorCreationOptions;
 import org.testng.Assert;
@@ -106,13 +107,13 @@ public class ActorReconstructionTest extends BaseTest {
     }
 
     @Override
-    public void saveCheckpoint(UniqueId actorId, UniqueId checkpointId) {
+    public void saveCheckpoint(ActorId actorId, UniqueId checkpointId) {
       // In practice, user should save the checkpoint id and data to a persistent store.
       // But for simplicity, we don't do that in this unit test.
     }
 
     @Override
-    public UniqueId loadCheckpoint(UniqueId actorId, List<Checkpoint> availableCheckpoints) {
+    public UniqueId loadCheckpoint(ActorId actorId, List<Checkpoint> availableCheckpoints) {
       // Restore previous value and return checkpoint id.
       this.value = 3;
       this.resumedFromCheckpoint = true;
@@ -120,7 +121,7 @@ public class ActorReconstructionTest extends BaseTest {
     }
 
     @Override
-    public void checkpointExpired(UniqueId actorId, UniqueId checkpointId) {
+    public void checkpointExpired(ActorId actorId, UniqueId checkpointId) {
     }
   }
 

java/test/src/main/java/org/ray/api/test/ClientExceptionTest.java

@@ -20,7 +20,7 @@ public class ClientExceptionTest extends BaseTest {
   @Test
   public void testWaitAndCrash() {
     TestUtils.skipTestUnderSingleProcess();
-    ObjectId randomId = ObjectId.randomId();
+    ObjectId randomId = ObjectId.fromRandom();
     RayObject<String> notExisting = new RayObjectImpl(randomId);
 
     Thread thread = new Thread(() -> {

java/test/src/main/java/org/ray/api/test/PlasmaStoreTest.java

@@ -13,7 +13,7 @@ public class PlasmaStoreTest extends BaseTest {
   @Test
   public void testPutWithDuplicateId() {
     TestUtils.skipTestUnderSingleProcess();
-    ObjectId objectId = ObjectId.randomId();
+    ObjectId objectId = ObjectId.fromRandom();
     AbstractRayRuntime runtime = (AbstractRayRuntime) Ray.internal();
     ObjectStoreProxy objectInterface = runtime.getObjectStoreProxy();
     objectInterface.put(objectId, 1);

java/test/src/main/java/org/ray/api/test/RaySerializerTest.java

@@ -1,6 +1,8 @@
 package org.ray.api.test;
 
 import org.ray.api.RayPyActor;
+import org.ray.api.id.ActorId;
+import org.ray.api.id.JobId;
 import org.ray.api.id.UniqueId;
 import org.ray.runtime.RayPyActorImpl;
 import org.ray.runtime.util.Serializer;
@@ -11,7 +13,7 @@ public class RaySerializerTest {
 
   @Test
   public void testSerializePyActor() {
-    final UniqueId pyActorId = UniqueId.randomId();
+    final ActorId pyActorId = ActorId.generateActorId(JobId.fromInt(1));
     RayPyActor pyActor = new RayPyActorImpl(pyActorId, "test", "RaySerializerTest");
     byte[] bytes = Serializer.encode(pyActor);
     RayPyActor result = Serializer.decode(bytes);

java/test/src/main/java/org/ray/api/test/RuntimeContextTest.java

@@ -3,6 +3,7 @@ package org.ray.api.test;
 import org.ray.api.Ray;
 import org.ray.api.RayActor;
 import org.ray.api.annotation.RayRemote;
+import org.ray.api.id.ActorId;
 import org.ray.api.id.JobId;
 import org.ray.api.id.UniqueId;
 import org.testng.Assert;
@@ -41,7 +42,7 @@ public class RuntimeContextTest extends BaseTest {
   @RayRemote
   public static class RuntimeContextTester {
 
-    public String testRuntimeContext(UniqueId actorId) {
+    public String testRuntimeContext(ActorId actorId) {
       Assert.assertEquals(JOB_ID, Ray.getRuntimeContext().getCurrentJobId());
       Assert.assertEquals(actorId, Ray.getRuntimeContext().getCurrentActorId());
       Assert.assertEquals(RAYLET_SOCKET_NAME, Ray.getRuntimeContext().getRayletSocketName());

java/test/src/main/java/org/ray/api/test/UniqueIdTest.java

@@ -3,6 +3,7 @@ package org.ray.api.test;
 import java.nio.ByteBuffer;
 import java.util.Arrays;
 import javax.xml.bind.DatatypeConverter;
+
 import org.ray.api.id.ObjectId;
 import org.ray.api.id.TaskId;
 import org.ray.api.id.UniqueId;
@@ -52,49 +53,26 @@ public class UniqueIdTest {
   @Test
   public void testComputeReturnId() {
     // Mock a taskId, and the lowest 4 bytes should be 0.
-    TaskId taskId = TaskId.fromHexString("123456789ABCDEF123456789ABCDEF00");
+    TaskId taskId = TaskId.fromHexString("123456789ABCDE123456789ABCDE");
 
-    ObjectId returnId = IdUtil.computeReturnId(taskId, 1);
+    ObjectId returnId = ObjectId.forReturn(taskId, 1);
-    Assert.assertEquals("123456789abcdef123456789abcdef0001000000", returnId.toString());
+    Assert.assertEquals("123456789abcde123456789abcde00c001000000", returnId.toString());
+    Assert.assertEquals(returnId.getTaskId(), taskId);
 
-    returnId = IdUtil.computeReturnId(taskId, 0x01020304);
+    returnId = ObjectId.forReturn(taskId, 0x01020304);
-    Assert.assertEquals("123456789abcdef123456789abcdef0004030201", returnId.toString());
+    Assert.assertEquals("123456789abcde123456789abcde00c004030201", returnId.toString());
-  }
-
-  @Test
-  public void testComputeTaskId() {
-    ObjectId objId = ObjectId.fromHexString("123456789ABCDEF123456789ABCDEF0034421980");
-    TaskId taskId = objId.getTaskId();
-
-    Assert.assertEquals("123456789abcdef123456789abcdef00", taskId.toString());
   }
 
   @Test
   public void testComputePutId() {
     // Mock a taskId, the lowest 4 bytes should be 0.
-    TaskId taskId = TaskId.fromHexString("123456789ABCDEF123456789ABCDEF00");
+    TaskId taskId = TaskId.fromHexString("123456789ABCDE123456789ABCDE");
 
-    ObjectId putId = IdUtil.computePutId(taskId, 1);
+    ObjectId putId = ObjectId.forPut(taskId, 1);
-    Assert.assertEquals("123456789ABCDEF123456789ABCDEF00FFFFFFFF".toLowerCase(), putId.toString());
+    Assert.assertEquals("123456789abcde123456789abcde008001000000".toLowerCase(), putId.toString());
 
-    putId = IdUtil.computePutId(taskId, 0x01020304);
+    putId = ObjectId.forPut(taskId, 0x01020304);
-    Assert.assertEquals("123456789ABCDEF123456789ABCDEF00FCFCFDFE".toLowerCase(), putId.toString());
+    Assert.assertEquals("123456789abcde123456789abcde008004030201".toLowerCase(), putId.toString());
-  }
-
-  @Test
-  public void testUniqueIdsAndByteBufferInterConversion() {
-    final int len = 5;
-    UniqueId[] ids = new UniqueId[len];
-    for (int i = 0; i < len; ++i) {
-      ids[i] = UniqueId.randomId();
-    }
-
-    ByteBuffer temp = IdUtil.concatIds(ids);
-    UniqueId[] res = IdUtil.getUniqueIdsFromByteBuffer(temp);
-
-    for (int i = 0; i < len; ++i) {
-      Assert.assertEquals(ids[i], res[i]);
-    }
   }
 
   @Test
@@ -104,24 +82,4 @@ public class UniqueIdTest {
     Assert.assertEquals(remainder, 787616861);
   }
 
-  @Test
-  void testConcateIds() {
-    String taskHexStr = "123456789ABCDEF123456789ABCDEF00";
-    String objectHexStr = taskHexStr + "01020304";
-    ObjectId objectId1 = ObjectId.fromHexString(objectHexStr);
-    ObjectId objectId2 = ObjectId.fromHexString(objectHexStr);
-    TaskId[] taskIds = new TaskId[2];
-    taskIds[0] = objectId1.getTaskId();
-    taskIds[1] = objectId2.getTaskId();
-    ObjectId[] objectIds = new ObjectId[2];
-    objectIds[0] = objectId1;
-    objectIds[1] = objectId2;
-    String taskHexCompareStr = taskHexStr + taskHexStr;
-    String objectHexCompareStr = objectHexStr + objectHexStr;
-    Assert.assertEquals(DatatypeConverter.printHexBinary(
-        IdUtil.concatIds(taskIds).array()), taskHexCompareStr);
-    Assert.assertEquals(DatatypeConverter.printHexBinary(
-        IdUtil.concatIds(objectIds).array()), objectHexCompareStr);
-  }
-
 }

python/ray/_raylet.pyx

@@ -86,10 +86,10 @@ cdef VectorToObjectIDs(c_vector[CObjectID] object_ids):
 
 
 def compute_put_id(TaskID task_id, int64_t put_index):
-    if put_index < 1 or put_index > kMaxTaskPuts:
+    if put_index < 1 or put_index > CObjectID.MaxObjectIndex():
         raise ValueError("The range of 'put_index' should be [1, %d]"
-                         % kMaxTaskPuts)
+                         % CObjectID.MaxObjectIndex())
-    return ObjectID(CObjectID.ForPut(task_id.native(), put_index).Binary())
+    return ObjectID(CObjectID.ForPut(task_id.native(), put_index, 0).Binary())
 
 
 def compute_task_id(ObjectID object_id):

python/ray/actor.py

@@ -310,7 +310,8 @@ class ActorClass(object):
             raise Exception("Actors cannot be created before ray.init() "
                             "has been called.")
 
-        actor_id = ActorID.from_random()
+        actor_id = ActorID.of(worker.current_job_id, worker.current_task_id,
+                              worker.task_context.task_index + 1)
         # The actor cursor is a dummy object representing the most recent
         # actor method invocation. For each subsequent method invocation,
         # the current cursor should be added as a dependency, and then

python/ray/includes/task.pxd

@@ -78,8 +78,9 @@ cdef extern from "ray/common/task/task_spec.h" namespace "ray" nogil:
 cdef extern from "ray/common/task/task_util.h" namespace "ray" nogil:
     cdef cppclass TaskSpecBuilder "ray::TaskSpecBuilder":
         TaskSpecBuilder &SetCommonTaskSpec(
-            const CLanguage &language, const c_vector[c_string] &function_descriptor,
+            const CTaskID &task_id, const CLanguage &language,
-            const CJobID &job_id, const CTaskID &parent_task_id, uint64_t parent_counter,
+            const c_vector[c_string] &function_descriptor, const CJobID &job_id,
+            const CTaskID &parent_task_id, uint64_t parent_counter,
             uint64_t num_returns, const unordered_map[c_string, double] &required_resources,
             const unordered_map[c_string, double] &required_placement_resources)
 

python/ray/includes/task.pxi

@@ -19,7 +19,7 @@ cdef class TaskSpec:
     cdef:
         unique_ptr[CTaskSpec] task_spec
 
-    def __init__(self, JobID job_id, function_descriptor, arguments,
+    def __init__(self, TaskID task_id, JobID job_id, function_descriptor, arguments,
                  int num_returns, TaskID parent_task_id, int parent_counter,
                  ActorID actor_creation_id,
                  ObjectID actor_creation_dummy_object_id,
@@ -51,6 +51,7 @@ cdef class TaskSpec:
 
         # Build common task spec.
         builder.SetCommonTaskSpec(
+            task_id.native(),
             LANGUAGE_PYTHON,
             c_function_descriptor,
             job_id.native(),

python/ray/includes/unique_ids.pxd

@@ -53,11 +53,21 @@ cdef extern from "ray/common/id.h" namespace "ray" nogil:
         @staticmethod
         CActorClassID FromBinary(const c_string &binary)
 
-    cdef cppclass CActorID "ray::ActorID"(CUniqueID):
+    cdef cppclass CActorID "ray::ActorID"(CBaseID[CActorID]):
 
         @staticmethod
         CActorID FromBinary(const c_string &binary)
 
+        @staticmethod
+        const CActorID Nil()
+
+        @staticmethod
+        size_t Size()
+
+        @staticmethod
+        CActorID Of(CJobID job_id, CTaskID parent_task_id, int64_t parent_task_counter)
+
+
     cdef cppclass CActorHandleID "ray::ActorHandleID"(CUniqueID):
 
         @staticmethod
@@ -103,8 +113,26 @@ cdef extern from "ray/common/id.h" namespace "ray" nogil:
         @staticmethod
         size_t Size()
 
+        @staticmethod
+        CTaskID ForDriverTask(const CJobID &job_id)
+
+        @staticmethod
+        CTaskID ForFakeTask()
+
+        @staticmethod
+        CTaskID ForActorCreationTask(CActorID actor_id)
+
+        @staticmethod
+        CTaskID ForActorTask(CJobID job_id, CTaskID parent_task_id, int64_t parent_task_counter, CActorID actor_id)
+
+        @staticmethod
+        CTaskID ForNormalTask(CJobID job_id, CTaskID parent_task_id, int64_t parent_task_counter)
+
     cdef cppclass CObjectID" ray::ObjectID"(CBaseID[CObjectID]):
 
+        @staticmethod
+        int64_t MaxObjectIndex()
+
         @staticmethod
         CObjectID FromBinary(const c_string &binary)
 
@@ -112,7 +140,7 @@ cdef extern from "ray/common/id.h" namespace "ray" nogil:
         const CObjectID Nil()
 
         @staticmethod
-        CObjectID ForPut(const CTaskID &task_id, int64_t index);
+        CObjectID ForPut(const CTaskID &task_id, int64_t index, int64_t transport_type);
 
         @staticmethod
         CObjectID ForTaskReturn(const CTaskID &task_id, int64_t index);

python/ray/includes/unique_ids.pxi

@@ -36,7 +36,6 @@ def check_id(b, size=kUniqueIDSize):
 
 cdef extern from "ray/common/constants.h" nogil:
     cdef int64_t kUniqueIDSize
-    cdef int64_t kMaxTaskPuts
 
 
 cdef class BaseID:
@@ -151,6 +150,9 @@ cdef class ObjectID(BaseID):
     def is_nil(self):
         return self.data.IsNil()
 
+    def task_id(self):
+        return TaskID(self.data.TaskId().Binary())
+
     cdef size_t hash(self):
         return self.data.Hash()
 
@@ -197,9 +199,35 @@ cdef class TaskID(BaseID):
         return CTaskID.Size()
 
     @classmethod
-    def from_random(cls):
+    def for_fake_task(cls):
-        return cls(os.urandom(CTaskID.Size()))
+        return cls(CTaskID.ForFakeTask().Binary())
 
+    @classmethod
+    def for_driver_task(cls, job_id):
+        return cls(CTaskID.ForDriverTask(CJobID.FromBinary(job_id.binary())).Binary())
+
+    @classmethod
+    def for_actor_creation_task(cls, actor_id):
+        assert isinstance(actor_id, ActorID)
+        return cls(CTaskID.ForActorCreationTask(CActorID.FromBinary(actor_id.binary())).Binary())
+
+    @classmethod
+    def for_actor_task(cls, job_id, parent_task_id, parent_task_counter, actor_id):
+        assert isinstance(job_id, JobID)
+        assert isinstance(parent_task_id, TaskID)
+        assert isinstance(actor_id, ActorID)
+        return cls(CTaskID.ForActorTask(CJobID.FromBinary(job_id.binary()),
+                                        CTaskID.FromBinary(parent_task_id.binary()),
+                                        parent_task_counter,
+                                        CActorID.FromBinary(actor_id.binary())).Binary())
+
+    @classmethod
+    def for_normal_task(cls, job_id, parent_task_id, parent_task_counter):
+        assert isinstance(job_id, JobID)
+        assert isinstance(parent_task_id, TaskID)
+        return cls(CTaskID.ForNormalTask(CJobID.FromBinary(job_id.binary()),
+                                         CTaskID.FromBinary(parent_task_id.binary()),
+                                         parent_task_counter).Binary())
 
 cdef class ClientID(UniqueID):
 
@@ -257,15 +285,47 @@ cdef class WorkerID(UniqueID):
     cdef CWorkerID native(self):
         return <CWorkerID>self.data
 
-cdef class ActorID(UniqueID):
+cdef class ActorID(BaseID):
+    cdef CActorID data
 
     def __init__(self, id):
-        check_id(id)
+        check_id(id, CActorID.Size())
         self.data = CActorID.FromBinary(<c_string>id)
 
     cdef CActorID native(self):
         return <CActorID>self.data
 
+    @classmethod
+    def of(cls, job_id, parent_task_id, parent_task_counter):
+        assert isinstance(job_id, JobID)
+        assert isinstance(parent_task_id, TaskID)
+        return cls(CActorID.Of(CJobID.FromBinary(job_id.binary()),
+                               CTaskID.FromBinary(parent_task_id.binary()),
+                               parent_task_counter).Binary())
+
+    @classmethod
+    def nil(cls):
+        return cls(CActorID.Nil().Binary())
+
+    @classmethod
+    def size(cls):
+        return CActorID.Size()
+
+    def binary(self):
+        return self.data.Binary()
+
+    def hex(self):
+        return decode(self.data.Hex())
+
+    def size(self):
+        return CActorID.Size()
+
+    def is_nil(self):
+        return self.data.IsNil()
+
+    cdef size_t hash(self):
+        return self.data.Hash()
+
 
 cdef class ActorHandleID(UniqueID):
 

python/ray/tests/test_basic.py

@@ -2520,13 +2520,14 @@ def test_global_state_api(shutdown_only):
     assert len(task_table) == 1
     assert driver_task_id == list(task_table.keys())[0]
     task_spec = task_table[driver_task_id]["TaskSpec"]
-    nil_id_hex = ray.ObjectID.nil().hex()
+    nil_unique_id_hex = ray.UniqueID.nil().hex()
+    nil_actor_id_hex = ray.ActorID.nil().hex()
 
     assert task_spec["TaskID"] == driver_task_id
-    assert task_spec["ActorID"] == nil_id_hex
+    assert task_spec["ActorID"] == nil_actor_id_hex
     assert task_spec["Args"] == []
     assert task_spec["JobID"] == job_id.hex()
-    assert task_spec["FunctionID"] == nil_id_hex
+    assert task_spec["FunctionID"] == nil_unique_id_hex
     assert task_spec["ReturnObjectIDs"] == []
 
     client_table = ray.nodes()
@@ -2551,7 +2552,7 @@ def test_global_state_api(shutdown_only):
     task_id = list(task_id_set)[0]
 
     task_spec = task_table[task_id]["TaskSpec"]
-    assert task_spec["ActorID"] == nil_id_hex
+    assert task_spec["ActorID"] == nil_actor_id_hex
     assert task_spec["Args"] == [1, "hi", x_id]
     assert task_spec["JobID"] == job_id.hex()
     assert task_spec["ReturnObjectIDs"] == [result_id]

python/ray/worker.py

@@ -200,7 +200,7 @@ class Worker(object):
                 # to the current task ID may not be correct. Generate a
                 # random task ID so that the backend can differentiate
                 # between different threads.
-                self._task_context.current_task_id = TaskID.from_random()
+                self._task_context.current_task_id = TaskID.for_fake_task()
                 if getattr(self, "_multithreading_warned", False) is not True:
                     logger.warning(
                         "Calling ray.get or ray.wait in a separate thread "
@@ -718,7 +718,24 @@ class Worker(object):
             function_descriptor_list = (
                 function_descriptor.get_function_descriptor_list())
             assert isinstance(job_id, JobID)
+
+            if actor_creation_id is not None and not actor_creation_id.is_nil(
+            ):
+                # This is an actor creation task.
+                task_id = TaskID.for_actor_creation_task(actor_creation_id)
+            elif actor_id is not None and not actor_id.is_nil():
+                # This is an actor task.
+                task_id = TaskID.for_actor_task(
+                    self.current_job_id, self.current_task_id,
+                    self.task_context.task_index, actor_id)
+            else:
+                # This is a normal task.
+                task_id = TaskID.for_normal_task(self.current_job_id,
+                                                 self.current_task_id,
+                                                 self.task_context.task_index)
+
             task = ray._raylet.TaskSpec(
+                task_id,
                 job_id,
                 function_descriptor_list,
                 args_for_raylet,
@@ -1917,6 +1934,7 @@ def connect(node,
 
         function_descriptor = FunctionDescriptor.for_driver_task()
         driver_task_spec = ray._raylet.TaskSpec(
+            TaskID.for_driver_task(worker.current_job_id),
             worker.current_job_id,
             function_descriptor.get_function_descriptor_list(),
             [],  # arguments.

src/ray/common/common_protocol.h

@@ -90,7 +90,6 @@ flatbuffers::Offset<flatbuffers::String> to_flatbuf(flatbuffers::FlatBufferBuild
 
 template <typename ID>
 ID from_flatbuf(const flatbuffers::String &string) {
-  RAY_CHECK(string.size() == ID::Size());
   return ID::FromBinary(string.str());
 }
 

src/ray/common/constants.h

@@ -7,30 +7,15 @@
 /// Length of Ray full-length IDs in bytes.
 constexpr size_t kUniqueIDSize = 20;
 
+/// Length of plasma ID in bytes.
+constexpr size_t kPlasmaIdSize = 20;
+
 /// An ObjectID's bytes are split into the task ID itself and the index of the
 /// object's creation. This is the maximum width of the object index in bits.
 constexpr int kObjectIdIndexSize = 32;
 static_assert(kObjectIdIndexSize % CHAR_BIT == 0,
               "ObjectID prefix not a multiple of bytes");
 
-/// Length of Ray TaskID in bytes. 32-bit integer is used for object index.
-constexpr int64_t kTaskIDSize = kUniqueIDSize - kObjectIdIndexSize / 8;
-
-/// The maximum number of objects that can be returned by a task when finishing
-/// execution. An ObjectID's bytes are split into the task ID itself and the
-/// index of the object's creation. A positive index indicates an object
-/// returned by the task, so the maximum number of objects that a task can
-/// return is the maximum positive value for an integer with bit-width
-/// `kObjectIdIndexSize`.
-constexpr int64_t kMaxTaskReturns = ((int64_t)1 << (kObjectIdIndexSize - 1)) - 1;
-/// The maximum number of objects that can be put by a task during execution.
-/// An ObjectID's bytes are split into the task ID itself and the index of the
-/// object's creation. A negative index indicates an object put by the task
-/// during execution, so the maximum number of objects that a task can put is
-/// the maximum negative value for an integer with bit-width
-/// `kObjectIdIndexSize`.
-constexpr int64_t kMaxTaskPuts = ((int64_t)1 << (kObjectIdIndexSize - 1));
-
 /// Prefix for the object table keys in redis.
 constexpr char kObjectTablePrefix[] = "ObjectTable";
 /// Prefix for the task table keys in redis.

src/ray/common/id.cc

@@ -2,12 +2,14 @@
 
 #include <limits.h>
 
+#include <algorithm>
 #include <chrono>
 #include <mutex>
 #include <random>
 
 #include "ray/common/constants.h"
 #include "ray/common/status.h"
+#include "ray/util/util.h"
 
 extern "C" {
 #include "ray/thirdparty/sha256.h"
@@ -18,13 +20,89 @@ extern "C" {
 
 namespace ray {
 
-std::mt19937 RandomlySeededMersenneTwister() {
+uint64_t MurmurHash64A(const void *key, int len, unsigned int seed);
-  auto seed = std::chrono::high_resolution_clock::now().time_since_epoch().count();
+
-  std::mt19937 seeded_engine(seed);
+/// A helper function to generate the unique bytes by hash.
-  return seeded_engine;
+std::string GenerateUniqueBytes(const JobID &job_id, const TaskID &parent_task_id,
+                                size_t parent_task_counter, size_t length) {
+  RAY_CHECK(length <= DIGEST_SIZE);
+  SHA256_CTX ctx;
+  sha256_init(&ctx);
+  sha256_update(&ctx, reinterpret_cast<const BYTE *>(job_id.Data()), job_id.Size());
+  sha256_update(&ctx, reinterpret_cast<const BYTE *>(parent_task_id.Data()),
+                parent_task_id.Size());
+  sha256_update(&ctx, (const BYTE *)&parent_task_counter, sizeof(parent_task_counter));
+
+  BYTE buff[DIGEST_SIZE];
+  sha256_final(&ctx, buff);
+  return std::string(buff, buff + length);
 }
 
-uint64_t MurmurHash64A(const void *key, int len, unsigned int seed);
+namespace {
+
+/// The bit offset of the flag `CreatedByTask` in a flags bytes.
+constexpr uint8_t kCreatedByTaskBitsOffset = 15;
+
+/// The bit offset of the flag `ObjectType` in a flags bytes.
+constexpr uint8_t kObjectTypeBitsOffset = 14;
+
+/// The bit offset of the flag `TransportType` in a flags bytes.
+constexpr uint8_t kTransportTypeBitsOffset = 11;
+
+/// The mask that is used to mask the flag `CreatedByTask`.
+constexpr ObjectIDFlagsType kCreatedByTaskFlagBitMask = 0x1 << kCreatedByTaskBitsOffset;
+
+/// The mask that is used to mask a bit to indicates the type of this object.
+/// So it can represent for 2 types.
+constexpr ObjectIDFlagsType kObjectTypeFlagBitMask = 0x1 << kObjectTypeBitsOffset;
+
+/// The mask that is used to mask 3 bits to indicate the type of transport.
+constexpr ObjectIDFlagsType kTransportTypeFlagBitMask = 0x7 << kTransportTypeBitsOffset;
+
+/// The implementations of helper functions.
+inline void SetCreatedByTaskFlag(bool created_by_task, ObjectIDFlagsType *flags) {
+  const ObjectIDFlagsType object_type_bits =
+      static_cast<ObjectIDFlagsType>(created_by_task) << kCreatedByTaskBitsOffset;
+  *flags = (*flags bitor object_type_bits);
+}
+
+inline void SetObjectTypeFlag(ObjectType object_type, ObjectIDFlagsType *flags) {
+  const ObjectIDFlagsType object_type_bits = static_cast<ObjectIDFlagsType>(object_type)
+                                             << kObjectTypeBitsOffset;
+  *flags = (*flags bitor object_type_bits);
+}
+
+inline void SetTransportTypeFlag(uint8_t transport_type, ObjectIDFlagsType *flags) {
+  const ObjectIDFlagsType transport_type_bits =
+      static_cast<ObjectIDFlagsType>(transport_type) << kTransportTypeBitsOffset;
+  *flags = (*flags bitor transport_type_bits);
+}
+
+inline bool CreatedByTask(ObjectIDFlagsType flags) {
+  return ((flags bitand kCreatedByTaskFlagBitMask) >> kCreatedByTaskBitsOffset) != 0x0;
+}
+
+inline ObjectType GetObjectType(ObjectIDFlagsType flags) {
+  const ObjectIDFlagsType object_type =
+      (flags bitand kObjectTypeFlagBitMask) >> kObjectTypeBitsOffset;
+  return static_cast<ObjectType>(object_type);
+}
+
+inline uint8_t GetTransportType(ObjectIDFlagsType flags) {
+  const ObjectIDFlagsType transport_type =
+      (flags bitand kTransportTypeFlagBitMask) >> kTransportTypeBitsOffset;
+  return static_cast<uint8_t>(transport_type);
+}
+
+}  // namespace
+
+template <typename T>
+void FillNil(T *data) {
+  RAY_CHECK(data != nullptr);
+  for (int i = 0; i < data->size(); i++) {
+    (*data)[i] = static_cast<uint8_t>(0xFF);
+  }
+}
 
 WorkerID ComputeDriverIdFromJob(const JobID &job_id) {
   std::vector<uint8_t> data(WorkerID::Size(), 0);
@@ -34,14 +112,44 @@ WorkerID ComputeDriverIdFromJob(const JobID &job_id) {
       std::string(reinterpret_cast<const char *>(data.data()), data.size()));
 }
 
+ObjectID ObjectID::FromPlasmaIdBinary(const std::string &from) {
+  RAY_CHECK(from.size() == kPlasmaIdSize);
+  return ObjectID::FromBinary(from.substr(0, ObjectID::kLength));
+}
+
 plasma::UniqueID ObjectID::ToPlasmaId() const {
+  static_assert(ObjectID::kLength <= kPlasmaIdSize,
+                "Currently length of ObjectID must be shorter than plasma's.");
+
   plasma::UniqueID result;
-  std::memcpy(result.mutable_data(), Data(), kUniqueIDSize);
+  std::memcpy(result.mutable_data(), Data(), ObjectID::Size());
+  std::fill_n(result.mutable_data() + ObjectID::Size(), kPlasmaIdSize - ObjectID::kLength,
+              0xFF);
   return result;
 }
 
 ObjectID::ObjectID(const plasma::UniqueID &from) {
-  std::memcpy(this->MutableData(), from.data(), kUniqueIDSize);
+  RAY_CHECK(from.size() <= ObjectID::Size()) << "Out of size.";
+  std::memcpy(this->MutableData(), from.data(), ObjectID::Size());
+}
+
+ObjectIDFlagsType ObjectID::GetFlags() const {
+  ObjectIDFlagsType flags;
+  std::memcpy(&flags, id_ + TaskID::kLength, sizeof(flags));
+  return flags;
+}
+bool ObjectID::CreatedByTask() const { return ::ray::CreatedByTask(this->GetFlags()); }
+
+bool ObjectID::IsPutObject() const {
+  return ::ray::GetObjectType(this->GetFlags()) == ObjectType::PUT_OBJECT;
+}
+
+bool ObjectID::IsReturnObject() const {
+  return ::ray::GetObjectType(this->GetFlags()) == ObjectType::RETURN_OBJECT;
+}
+
+uint8_t ObjectID::GetTransportType() const {
+  return ::ray::GetTransportType(this->GetFlags());
 }
 
 // This code is from https://sites.google.com/site/murmurhash/
@@ -93,6 +201,78 @@ uint64_t MurmurHash64A(const void *key, int len, unsigned int seed) {
   return h;
 }
 
+ActorID ActorID::Of(const JobID &job_id, const TaskID &parent_task_id,
+                    const size_t parent_task_counter) {
+  auto data = GenerateUniqueBytes(job_id, parent_task_id, parent_task_counter,
+                                  ActorID::kUniqueBytesLength);
+  std::copy_n(job_id.Data(), JobID::kLength, std::back_inserter(data));
+  RAY_CHECK(data.size() == kLength);
+  return ActorID::FromBinary(data);
+}
+
+ActorID ActorID::NilFromJob(const JobID &job_id) {
+  std::string data(kUniqueBytesLength, 0);
+  FillNil(&data);
+  std::copy_n(job_id.Data(), JobID::kLength, std::back_inserter(data));
+  RAY_CHECK(data.size() == kLength);
+  return ActorID::FromBinary(data);
+}
+
+JobID ActorID::JobId() const {
+  RAY_CHECK(!IsNil());
+  return JobID::FromBinary(std::string(
+      reinterpret_cast<const char *>(this->Data() + kUniqueBytesLength), JobID::kLength));
+}
+
+TaskID TaskID::ForDriverTask(const JobID &job_id) {
+  std::string data(kUniqueBytesLength, 0);
+  FillNil(&data);
+  const auto dummy_actor_id = ActorID::NilFromJob(job_id);
+  std::copy_n(dummy_actor_id.Data(), ActorID::kLength, std::back_inserter(data));
+  RAY_CHECK(data.size() == TaskID::kLength);
+  return TaskID::FromBinary(data);
+}
+
+TaskID TaskID::ForFakeTask() {
+  std::string data(kLength, 0);
+  FillRandom(&data);
+  return TaskID::FromBinary(data);
+}
+
+TaskID TaskID::ForActorCreationTask(const ActorID &actor_id) {
+  std::string data(kUniqueBytesLength, 0);
+  FillNil(&data);
+  std::copy_n(actor_id.Data(), ActorID::kLength, std::back_inserter(data));
+  RAY_CHECK(data.size() == TaskID::kLength);
+  return TaskID::FromBinary(data);
+}
+
+TaskID TaskID::ForActorTask(const JobID &job_id, const TaskID &parent_task_id,
+                            size_t parent_task_counter, const ActorID &actor_id) {
+  std::string data = GenerateUniqueBytes(job_id, parent_task_id, parent_task_counter,
+                                         TaskID::kUniqueBytesLength);
+  std::copy_n(actor_id.Data(), ActorID::kLength, std::back_inserter(data));
+  RAY_CHECK(data.size() == TaskID::kLength);
+  return TaskID::FromBinary(data);
+}
+
+TaskID TaskID::ForNormalTask(const JobID &job_id, const TaskID &parent_task_id,
+                             size_t parent_task_counter) {
+  std::string data = GenerateUniqueBytes(job_id, parent_task_id, parent_task_counter,
+                                         TaskID::kUniqueBytesLength);
+  const auto dummy_actor_id = ActorID::NilFromJob(job_id);
+  std::copy_n(dummy_actor_id.Data(), ActorID::kLength, std::back_inserter(data));
+  RAY_CHECK(data.size() == TaskID::kLength);
+  return TaskID::FromBinary(data);
+}
+
+ActorID TaskID::ActorId() const {
+  return ActorID::FromBinary(std::string(
+      reinterpret_cast<const char *>(id_ + kUniqueBytesLength), ActorID::Size()));
+}
+
+JobID TaskID::JobId() const { return ActorId().JobId(); }
+
 TaskID TaskID::ComputeDriverTaskId(const WorkerID &driver_id) {
   std::string driver_id_str = driver_id.Binary();
   driver_id_str.resize(Size());
@@ -100,41 +280,70 @@ TaskID TaskID::ComputeDriverTaskId(const WorkerID &driver_id) {
 }
 
 TaskID ObjectID::TaskId() const {
+  if (!CreatedByTask()) {
+    // TODO(qwang): Should be RAY_CHECK here.
+    RAY_LOG(WARNING) << "Shouldn't call this on a non-task object id: " << this->Hex();
+  }
   return TaskID::FromBinary(
       std::string(reinterpret_cast<const char *>(id_), TaskID::Size()));
 }
 
-ObjectID ObjectID::ForPut(const TaskID &task_id, int64_t put_index) {
+ObjectID ObjectID::ForPut(const TaskID &task_id, ObjectIDIndexType put_index,
-  RAY_CHECK(put_index >= 1 && put_index <= kMaxTaskPuts) << "index=" << put_index;
+                          uint8_t transport_type) {
-  ObjectID object_id;
+  RAY_CHECK(put_index >= 1 && put_index <= kMaxObjectIndex) << "index=" << put_index;
-  std::memcpy(object_id.id_, task_id.Binary().c_str(), task_id.Size());
+
-  object_id.index_ = -put_index;
+  ObjectIDFlagsType flags = 0x0000;
-  return object_id;
+  SetCreatedByTaskFlag(true, &flags);
+  SetObjectTypeFlag(ObjectType::PUT_OBJECT, &flags);
+
+  SetTransportTypeFlag(transport_type, &flags);
+
+  return GenerateObjectId(task_id.Binary(), flags, put_index);
 }
 
-ObjectID ObjectID::ForTaskReturn(const TaskID &task_id, int64_t return_index) {
+ObjectIDIndexType ObjectID::ObjectIndex() const {
-  RAY_CHECK(return_index >= 1 && return_index <= kMaxTaskReturns)
+  ObjectIDIndexType index;
+  std::memcpy(&index, id_ + TaskID::kLength + kFlagsBytesLength, sizeof(index));
+  return index;
+}
+
+ObjectID ObjectID::ForTaskReturn(const TaskID &task_id, ObjectIDIndexType return_index,
+                                 uint8_t transport_type) {
+  RAY_CHECK(return_index >= 1 && return_index <= kMaxObjectIndex)
       << "index=" << return_index;
-  ObjectID object_id;
+
-  std::memcpy(object_id.id_, task_id.Binary().c_str(), task_id.Size());
+  ObjectIDFlagsType flags = 0x0000;
-  object_id.index_ = return_index;
+  SetCreatedByTaskFlag(true, &flags);
-  return object_id;
+  SetObjectTypeFlag(ObjectType::RETURN_OBJECT, &flags);
+  SetTransportTypeFlag(transport_type, &flags);
+
+  return GenerateObjectId(task_id.Binary(), flags, return_index);
 }
 
-const TaskID GenerateTaskId(const JobID &job_id, const TaskID &parent_task_id,
+ObjectID ObjectID::FromRandom() {
-                            int parent_task_counter) {
+  ObjectIDFlagsType flags = 0x0000;
-  // Compute hashes.
+  SetCreatedByTaskFlag(false, &flags);
-  SHA256_CTX ctx;
+  // No need to set transport type for a random object id.
-  sha256_init(&ctx);
+  // No need to assign put_index/return_index bytes.
-  sha256_update(&ctx, reinterpret_cast<const BYTE *>(job_id.Data()), job_id.Size());
+  std::vector<uint8_t> task_id_bytes(TaskID::kLength, 0x0);
-  sha256_update(&ctx, reinterpret_cast<const BYTE *>(parent_task_id.Data()),
+  FillRandom(&task_id_bytes);
-                parent_task_id.Size());
-  sha256_update(&ctx, (const BYTE *)&parent_task_counter, sizeof(parent_task_counter));
 
-  // Compute the final task ID from the hash.
+  return GenerateObjectId(
-  BYTE buff[DIGEST_SIZE];
+      std::string(reinterpret_cast<const char *>(task_id_bytes.data()),
-  sha256_final(&ctx, buff);
+                  task_id_bytes.size()),
-  return TaskID::FromBinary(std::string(buff, buff + TaskID::Size()));
+      flags);
+}
+
+ObjectID ObjectID::GenerateObjectId(const std::string &task_id_binary,
+                                    ObjectIDFlagsType flags,
+                                    ObjectIDIndexType object_index) {
+  RAY_CHECK(task_id_binary.size() == TaskID::Size());
+  ObjectID ret = ObjectID::Nil();
+  std::memcpy(ret.id_, task_id_binary.c_str(), TaskID::kLength);
+  std::memcpy(ret.id_ + TaskID::kLength, &flags, sizeof(flags));
+  std::memcpy(ret.id_ + TaskID::kLength + kFlagsBytesLength, &object_index,
+              sizeof(object_index));
+  return ret;
 }
 
 const ActorHandleID ComputeNextActorHandleId(const ActorHandleID &actor_handle_id,
@@ -172,6 +381,7 @@ JobID JobID::FromInt(uint32_t value) {
 
 ID_OSTREAM_OPERATOR(UniqueID);
 ID_OSTREAM_OPERATOR(JobID);
+ID_OSTREAM_OPERATOR(ActorID);
 ID_OSTREAM_OPERATOR(TaskID);
 ID_OSTREAM_OPERATOR(ObjectID);
 

src/ray/common/id.h

@@ -13,10 +13,12 @@
 #include "plasma/common.h"
 #include "ray/common/constants.h"
 #include "ray/util/logging.h"
+#include "ray/util/util.h"
 #include "ray/util/visibility.h"
 
 namespace ray {
 
+class TaskID;
 class WorkerID;
 class UniqueID;
 class JobID;
@@ -27,13 +29,29 @@ class JobID;
 /// A helper function that get the `DriverID` of the given job.
 WorkerID ComputeDriverIdFromJob(const JobID &job_id);
 
+/// The type of this object. `PUT_OBJECT` indicates this object
+/// is generated through `ray.put` during the task's execution.
+/// And `RETURN_OBJECT` indicates this object is the return value
+/// of a task.
+enum class ObjectType : uint8_t {
+  PUT_OBJECT = 0x0,
+  RETURN_OBJECT = 0x1,
+};
+
+using ObjectIDFlagsType = uint16_t;
+using ObjectIDIndexType = uint32_t;
+
 // Declaration.
-std::mt19937 RandomlySeededMersenneTwister();
 uint64_t MurmurHash64A(const void *key, int len, unsigned int seed);
 
 // Change the compiler alignment to 1 byte (default is 8).
 #pragma pack(push, 1)
 
+/// The `ID`s of Ray.
+///
+/// Please refer to the specification of Ray UniqueIDs.
+/// https://github.com/ray-project/ray/blob/master/src/ray/design_docs/id_specification.md
+
 template <typename T>
 class BaseID {
  public:
@@ -78,78 +96,251 @@ class UniqueID : public BaseID<UniqueID> {
 
 class JobID : public BaseID<JobID> {
  public:
-  static constexpr int64_t length = 4;
+  static constexpr int64_t kLength = 4;
 
-  // TODO(qwang): Use `uint32_t` to store the data.
   static JobID FromInt(uint32_t value);
 
-  static size_t Size() { return length; }
+  static size_t Size() { return kLength; }
 
   static JobID FromRandom() = delete;
 
   JobID() : BaseID() {}
 
  private:
-  uint8_t id_[length];
+  uint8_t id_[kLength];
+};
+
+class ActorID : public BaseID<ActorID> {
+ private:
+  static constexpr size_t kUniqueBytesLength = 4;
+
+ public:
+  /// Length of `ActorID` in bytes.
+  static constexpr size_t kLength = kUniqueBytesLength + JobID::kLength;
+
+  /// Size of `ActorID` in bytes.
+  ///
+  /// \return Size of `ActorID` in bytes.
+  static size_t Size() { return kLength; }
+
+  /// Creates an `ActorID` by hashing the given information.
+  ///
+  /// \param job_id The job id to which this actor belongs.
+  /// \param parent_task_id The id of the task which created this actor.
+  /// \param parent_task_counter The counter of the parent task.
+  ///
+  /// \return The random `ActorID`.
+  static ActorID Of(const JobID &job_id, const TaskID &parent_task_id,
+                    const size_t parent_task_counter);
+
+  /// Creates a nil ActorID with the given job.
+  ///
+  /// \param job_id The job id to which this actor belongs.
+  ///
+  /// \return The `ActorID` with unique bytes being nil.
+  static ActorID NilFromJob(const JobID &job_id);
+
+  static ActorID FromRandom() = delete;
+
+  /// Constructor of `ActorID`.
+  ActorID() : BaseID() {}
+
+  /// Get the job id to which this actor belongs.
+  ///
+  /// \return The job id to which this actor belongs.
+  JobID JobId() const;
+
+ private:
+  uint8_t id_[kLength];
 };
 
 class TaskID : public BaseID<TaskID> {
+ private:
+  static constexpr size_t kUniqueBytesLength = 6;
+
  public:
+  static constexpr size_t kLength = kUniqueBytesLength + ActorID::kLength;
+
   TaskID() : BaseID() {}
-  static size_t Size() { return kTaskIDSize; }
+
+  static size_t Size() { return kLength; }
+
   static TaskID ComputeDriverTaskId(const WorkerID &driver_id);
 
+  static TaskID FromRandom() = delete;
+
+  /// The ID generated for driver task.
+  static TaskID ForDriverTask(const JobID &job_id);
+
+  /// Generate driver task id for the given job.
+  static TaskID ForFakeTask();
+
+  /// Creates a TaskID for an actor creation task.
+  ///
+  /// \param actor_id The ID of the actor that will be created
+  ///        by this actor creation task.
+  ///
+  /// \return The ID of the actor creation task.
+  static TaskID ForActorCreationTask(const ActorID &actor_id);
+
+  /// Creates a TaskID for actor task.
+  ///
+  /// \param job_id The ID of the job to which this task belongs.
+  /// \param parent_task_id The ID of the parent task which submitted this task.
+  /// \param parent_task_counter A count of the number of tasks submitted by the
+  ///        parent task before this one.
+  /// \param actor_id The ID of the actor to which this task belongs.
+  ///
+  /// \return The ID of the actor task.
+  static TaskID ForActorTask(const JobID &job_id, const TaskID &parent_task_id,
+                             size_t parent_task_counter, const ActorID &actor_id);
+
+  /// Creates a TaskID for normal task.
+  ///
+  /// \param job_id The ID of the job to which this task belongs.
+  /// \param parent_task_id The ID of the parent task which submitted this task.
+  /// \param parent_task_counter A count of the number of tasks submitted by the
+  ///        parent task before this one.
+  ///
+  /// \return The ID of the normal task.
+  static TaskID ForNormalTask(const JobID &job_id, const TaskID &parent_task_id,
+                              size_t parent_task_counter);
+
+  /// Get the id of the actor to which this task belongs.
+  ///
+  /// \return The `ActorID` of the actor which creates this task.
+  ActorID ActorId() const;
+
+  /// Get the id of the job to which this task belongs.
+  ///
+  /// \return The `JobID` of the job which creates this task.
+  JobID JobId() const;
+
  private:
-  uint8_t id_[kTaskIDSize];
+  uint8_t id_[kLength];
 };
 
 class ObjectID : public BaseID<ObjectID> {
+ private:
+  static constexpr size_t kIndexBytesLength = sizeof(ObjectIDIndexType);
+
+  static constexpr size_t kFlagsBytesLength = sizeof(ObjectIDFlagsType);
+
  public:
+  /// The maximum number of objects that can be returned or put by a task.
+  static constexpr int64_t kMaxObjectIndex = ((int64_t)1 << kObjectIdIndexSize) - 1;
+
+  /// The length of ObjectID in bytes.
+  static constexpr size_t kLength =
+      kIndexBytesLength + kFlagsBytesLength + TaskID::kLength;
+
   ObjectID() : BaseID() {}
-  static size_t Size() { return kUniqueIDSize; }
+
+  /// The maximum index of object.
+  ///
+  /// It also means the max number of objects created (put or return) by one task.
+  ///
+  /// \return The maximum index of object.
+  static uint64_t MaxObjectIndex() { return kMaxObjectIndex; }
+
+  static size_t Size() { return kLength; }
+
+  /// Generate ObjectID by the given binary string of a plasma id.
+  ///
+  /// \param from The binary string of the given plasma id.
+  /// \return The ObjectID converted from a binary string of the plasma id.
+  static ObjectID FromPlasmaIdBinary(const std::string &from);
+
   plasma::ObjectID ToPlasmaId() const;
+
   ObjectID(const plasma::UniqueID &from);
 
   /// Get the index of this object in the task that created it.
   ///
   /// \return The index of object creation according to the task that created
-  /// this object. This is positive if the task returned the object and negative
+  /// this object.
-  /// if created by a put.
+  ObjectIDIndexType ObjectIndex() const;
-  int32_t ObjectIndex() const { return index_; }
 
   /// Compute the task ID of the task that created the object.
   ///
   /// \return The task ID of the task that created this object.
   TaskID TaskId() const;
 
+  /// Whether this object is created by a task.
+  ///
+  /// \return True if this object is created by a task, otherwise false.
+  bool CreatedByTask() const;
+
+  /// Whether this object was created through `ray.put`.
+  ///
+  /// \return True if this object was created through `ray.put`.
+  bool IsPutObject() const;
+
+  /// Whether this object was created as a return object of a task.
+  ///
+  /// \return True if this object is a return value of a task.
+  bool IsReturnObject() const;
+
+  /// Get the transport type of this object.
+  ///
+  /// \return The type of the transport which is used to transfer this object.
+  uint8_t GetTransportType() const;
+
   /// Compute the object ID of an object put by the task.
   ///
   /// \param task_id The task ID of the task that created the object.
   /// \param index What index of the object put in the task.
+  /// \param transport_type Which type of the transport that is used to
+  ///        transfer this object.
+  ///
   /// \return The computed object ID.
-  static ObjectID ForPut(const TaskID &task_id, int64_t put_index);
+  static ObjectID ForPut(const TaskID &task_id, ObjectIDIndexType put_index,
+                         uint8_t transport_type);
 
   /// Compute the object ID of an object returned by the task.
   ///
   /// \param task_id The task ID of the task that created the object.
   /// \param return_index What index of the object returned by in the task.
+  /// \param transport_type Which type of the transport that is used to
+  ///        transfer this object.
+  ///
   /// \return The computed object ID.
-  static ObjectID ForTaskReturn(const TaskID &task_id, int64_t return_index);
+  static ObjectID ForTaskReturn(const TaskID &task_id, ObjectIDIndexType return_index,
+                                uint8_t transport_type);
+
+  /// Create an object id randomly.
+  ///
+  /// \param transport_type Which type of the transport that is used to
+  ///        transfer this object.
+  ///
+  /// \return A random object id.
+  static ObjectID FromRandom();
 
  private:
-  uint8_t id_[kTaskIDSize];
+  /// A helper method to generate an ObjectID.
-  int32_t index_;
+  static ObjectID GenerateObjectId(const std::string &task_id_binary,
+                                   ObjectIDFlagsType flags,
+                                   ObjectIDIndexType object_index = 0);
+
+  /// Get the flags out of this object id.
+  ObjectIDFlagsType GetFlags() const;
+
+ private:
+  uint8_t id_[kLength];
 };
 
-static_assert(sizeof(JobID) == JobID::length + sizeof(size_t),
+static_assert(sizeof(JobID) == JobID::kLength + sizeof(size_t),
               "JobID size is not as expected");
-static_assert(sizeof(TaskID) == kTaskIDSize + sizeof(size_t),
+static_assert(sizeof(ActorID) == ActorID::kLength + sizeof(size_t),
+              "ActorID size is not as expected");
+static_assert(sizeof(TaskID) == TaskID::kLength + sizeof(size_t),
               "TaskID size is not as expected");
-static_assert(sizeof(ObjectID) == sizeof(int32_t) + sizeof(TaskID),
+static_assert(sizeof(ObjectID) == ObjectID::kLength + sizeof(size_t),
               "ObjectID size is not as expected");
 
 std::ostream &operator<<(std::ostream &os, const UniqueID &id);
 std::ostream &operator<<(std::ostream &os, const JobID &id);
+std::ostream &operator<<(std::ostream &os, const ActorID &id);
 std::ostream &operator<<(std::ostream &os, const TaskID &id);
 std::ostream &operator<<(std::ostream &os, const ObjectID &id);
 
@@ -178,15 +369,6 @@ std::ostream &operator<<(std::ostream &os, const ObjectID &id);
 // Restore the compiler alignment to defult (8 bytes).
 #pragma pack(pop)
 
-/// Generate a task ID from the given info.
-///
-/// \param job_id The job that creates the task.
-/// \param parent_task_id The parent task of this task.
-/// \param parent_task_counter The task index of the worker.
-/// \return The task ID generated from the given info.
-const TaskID GenerateTaskId(const JobID &job_id, const TaskID &parent_task_id,
-                            int parent_task_counter);
-
 /// Compute the next actor handle ID of a new actor handle during a fork operation.
 ///
 /// \param actor_handle_id The actor handle ID of original actor.
@@ -205,22 +387,14 @@ BaseID<T>::BaseID() {
 template <typename T>
 T BaseID<T>::FromRandom() {
   std::string data(T::Size(), 0);
-  // NOTE(pcm): The right way to do this is to have one std::mt19937 per
+  FillRandom(&data);
-  // thread (using the thread_local keyword), but that's not supported on
-  // older versions of macOS (see https://stackoverflow.com/a/29929949)
-  static std::mutex random_engine_mutex;
-  std::lock_guard<std::mutex> lock(random_engine_mutex);
-  static std::mt19937 generator = RandomlySeededMersenneTwister();
-  std::uniform_int_distribution<uint32_t> dist(0, std::numeric_limits<uint8_t>::max());
-  for (int i = 0; i < T::Size(); i++) {
-    data[i] = static_cast<uint8_t>(dist(generator));
-  }
   return T::FromBinary(data);
 }
 
 template <typename T>
 T BaseID<T>::FromBinary(const std::string &binary) {
-  RAY_CHECK(binary.size() == T::Size());
+  RAY_CHECK(binary.size() == T::Size())
+      << "expected size is " << T::Size() << ", but got " << binary.size();
   T t = T::Nil();
   std::memcpy(t.MutableData(), binary.data(), T::Size());
   return t;
@@ -302,6 +476,7 @@ namespace std {
 
 DEFINE_UNIQUE_ID(UniqueID);
 DEFINE_UNIQUE_ID(JobID);
+DEFINE_UNIQUE_ID(ActorID);
 DEFINE_UNIQUE_ID(TaskID);
 DEFINE_UNIQUE_ID(ObjectID);
 #include "id_def.h"

src/ray/common/id_def.h

@@ -6,7 +6,6 @@
 
 DEFINE_UNIQUE_ID(FunctionID)
 DEFINE_UNIQUE_ID(ActorClassID)
-DEFINE_UNIQUE_ID(ActorID)
 DEFINE_UNIQUE_ID(ActorHandleID)
 DEFINE_UNIQUE_ID(ActorCheckpointID)
 DEFINE_UNIQUE_ID(WorkerID)

src/ray/common/id_test.cc

@@ -0,0 +1,107 @@
+#include "gtest/gtest.h"
+
+#include "ray/common/common_protocol.h"
+#include "ray/common/task/task_spec.h"
+
+namespace ray {
+
+void TestReturnObjectId(const TaskID &task_id, int64_t return_index,
+                        uint8_t transport_type) {
+  // Round trip test for computing the object ID for a task's return value,
+  // then computing the task ID that created the object.
+  ObjectID return_id = ObjectID::ForTaskReturn(task_id, return_index, transport_type);
+  ASSERT_TRUE(return_id.CreatedByTask());
+  ASSERT_TRUE(return_id.IsReturnObject());
+  ASSERT_FALSE(return_id.IsPutObject());
+  ASSERT_EQ(return_id.TaskId(), task_id);
+  ASSERT_TRUE(transport_type == return_id.GetTransportType());
+  ASSERT_EQ(return_id.ObjectIndex(), return_index);
+}
+
+void TestPutObjectId(const TaskID &task_id, int64_t put_index) {
+  // Round trip test for computing the object ID for a task's put value, then
+  // computing the task ID that created the object.
+  ObjectID put_id = ObjectID::ForPut(task_id, put_index, 1);
+  ASSERT_TRUE(put_id.CreatedByTask());
+  ASSERT_FALSE(put_id.IsReturnObject());
+  ASSERT_TRUE(put_id.IsPutObject());
+  ASSERT_EQ(put_id.TaskId(), task_id);
+  ASSERT_TRUE(1 == put_id.GetTransportType());
+  ASSERT_EQ(put_id.ObjectIndex(), put_index);
+}
+
+void TestRandomObjectId() {
+  // Round trip test for computing the object ID from random.
+  const ObjectID random_object_id = ObjectID::FromRandom();
+  ASSERT_FALSE(random_object_id.CreatedByTask());
+}
+
+const static JobID kDefaultJobId = JobID::FromInt(199);
+
+const static TaskID kDefaultDriverTaskId = TaskID::ForDriverTask(kDefaultJobId);
+
+TEST(ActorIDTest, TestActorID) {
+  {
+    // test from binary
+    const ActorID actor_id_1 = ActorID::Of(kDefaultJobId, kDefaultDriverTaskId, 1);
+    const auto actor_id_1_binary = actor_id_1.Binary();
+    const auto actor_id_2 = ActorID::FromBinary(actor_id_1_binary);
+    ASSERT_EQ(actor_id_1, actor_id_2);
+  }
+
+  {
+    // test get job id
+    const ActorID actor_id = ActorID::Of(kDefaultJobId, kDefaultDriverTaskId, 1);
+    ASSERT_EQ(kDefaultJobId, actor_id.JobId());
+  }
+}
+
+TEST(TaskIDTest, TestTaskID) {
+  // Round trip test for task ID.
+  {
+    const ActorID actor_id = ActorID::Of(kDefaultJobId, kDefaultDriverTaskId, 1);
+    const TaskID task_id_1 =
+        TaskID::ForActorTask(kDefaultJobId, kDefaultDriverTaskId, 1, actor_id);
+    ASSERT_EQ(actor_id, task_id_1.ActorId());
+  }
+}
+
+TEST(ObjectIDTest, TestObjectID) {
+  const static ActorID default_actor_id =
+      ActorID::Of(kDefaultJobId, kDefaultDriverTaskId, 1);
+  const static TaskID default_task_id =
+      TaskID::ForActorTask(kDefaultJobId, kDefaultDriverTaskId, 1, default_actor_id);
+
+  {
+    // test for put
+    TestPutObjectId(default_task_id, 1);
+    TestPutObjectId(default_task_id, 2);
+    TestPutObjectId(default_task_id, ObjectID::kMaxObjectIndex);
+  }
+
+  {
+    // test for return
+    TestReturnObjectId(default_task_id, 1, 2);
+    TestReturnObjectId(default_task_id, 2, 3);
+    TestReturnObjectId(default_task_id, ObjectID::kMaxObjectIndex, 4);
+  }
+
+  {
+    // test random object id
+    TestRandomObjectId();
+  }
+}
+
+TEST(NilTest, TestIsNil) {
+  ASSERT_TRUE(TaskID().IsNil());
+  ASSERT_TRUE(TaskID::Nil().IsNil());
+  ASSERT_TRUE(ObjectID().IsNil());
+  ASSERT_TRUE(ObjectID::Nil().IsNil());
+}
+
+}  // namespace ray
+
+int main(int argc, char **argv) {
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}

src/ray/common/task/task_spec.cc

@@ -38,7 +38,7 @@ size_t TaskSpecification::NumArgs() const { return message_->args_size(); }
 size_t TaskSpecification::NumReturns() const { return message_->num_returns(); }
 
 ObjectID TaskSpecification::ReturnId(size_t return_index) const {
-  return ObjectID::ForTaskReturn(TaskId(), return_index + 1);
+  return ObjectID::ForTaskReturn(TaskId(), return_index + 1, /*transport_type=*/0);
 }
 
 bool TaskSpecification::ArgByRef(size_t arg_index) const {

src/ray/common/task/task_test.cc

@@ -1,54 +0,0 @@
-#include "gtest/gtest.h"
-
-#include "ray/common/common_protocol.h"
-#include "ray/common/task/task_spec.h"
-
-namespace ray {
-
-void TestTaskReturnId(const TaskID &task_id, int64_t return_index) {
-  // Round trip test for computing the object ID for a task's return value,
-  // then computing the task ID that created the object.
-  ObjectID return_id = ObjectID::ForTaskReturn(task_id, return_index);
-  ASSERT_EQ(return_id.TaskId(), task_id);
-  ASSERT_EQ(return_id.ObjectIndex(), return_index);
-}
-
-void TestTaskPutId(const TaskID &task_id, int64_t put_index) {
-  // Round trip test for computing the object ID for a task's put value, then
-  // computing the task ID that created the object.
-  ObjectID put_id = ObjectID::ForPut(task_id, put_index);
-  ASSERT_EQ(put_id.TaskId(), task_id);
-  ASSERT_EQ(put_id.ObjectIndex(), -1 * put_index);
-}
-
-TEST(TaskSpecTest, TestTaskReturnIds) {
-  TaskID task_id = TaskID::FromRandom();
-
-  // Check that we can compute between a task ID and the object IDs of its
-  // return values and puts.
-  TestTaskReturnId(task_id, 1);
-  TestTaskReturnId(task_id, 2);
-  TestTaskReturnId(task_id, kMaxTaskReturns);
-  TestTaskPutId(task_id, 1);
-  TestTaskPutId(task_id, 2);
-  TestTaskPutId(task_id, kMaxTaskPuts);
-}
-
-TEST(IdPropertyTest, TestIdProperty) {
-  TaskID task_id = TaskID::FromRandom();
-  ASSERT_EQ(task_id, TaskID::FromBinary(task_id.Binary()));
-  ObjectID object_id = ObjectID::FromRandom();
-  ASSERT_EQ(object_id, ObjectID::FromBinary(object_id.Binary()));
-
-  ASSERT_TRUE(TaskID().IsNil());
-  ASSERT_TRUE(TaskID::Nil().IsNil());
-  ASSERT_TRUE(ObjectID().IsNil());
-  ASSERT_TRUE(ObjectID::Nil().IsNil());
-}
-
-}  // namespace ray
-
-int main(int argc, char **argv) {
-  ::testing::InitGoogleTest(&argc, argv);
-  return RUN_ALL_TESTS();
-}

src/ray/common/task/task_util.h

@@ -22,9 +22,9 @@ class TaskSpecBuilder {
   ///
   /// \return Reference to the builder object itself.
   TaskSpecBuilder &SetCommonTaskSpec(
-      const Language &language, const std::vector<std::string> &function_descriptor,
+      const TaskID &task_id, const Language &language,
-      const JobID &job_id, const TaskID &parent_task_id, uint64_t parent_counter,
+      const std::vector<std::string> &function_descriptor, const JobID &job_id,
-      uint64_t num_returns,
+      const TaskID &parent_task_id, uint64_t parent_counter, uint64_t num_returns,
       const std::unordered_map<std::string, double> &required_resources,
       const std::unordered_map<std::string, double> &required_placement_resources) {
     message_->set_type(TaskType::NORMAL_TASK);
@@ -33,8 +33,7 @@ class TaskSpecBuilder {
       message_->add_function_descriptor(fd);
     }
     message_->set_job_id(job_id.Binary());
-    message_->set_task_id(
+    message_->set_task_id(task_id.Binary());
-        GenerateTaskId(job_id, parent_task_id, parent_counter).Binary());
     message_->set_parent_task_id(parent_task_id.Binary());
     message_->set_parent_counter(parent_counter);
     message_->set_num_returns(num_returns);

src/ray/core_worker/context.cc

@@ -6,7 +6,7 @@ namespace ray {
 /// per-thread context for core worker.
 struct WorkerThreadContext {
   WorkerThreadContext()
-      : current_task_id_(TaskID::FromRandom()), task_index_(0), put_index_(0) {}
+      : current_task_id_(TaskID::ForFakeTask()), task_index_(0), put_index_(0) {}
 
   int GetNextTaskIndex() { return ++task_index_; }
 
@@ -54,8 +54,9 @@ WorkerContext::WorkerContext(WorkerType worker_type, const JobID &job_id)
   // For worker main thread which initializes the WorkerContext,
   // set task_id according to whether current worker is a driver.
   // (For other threads it's set to random ID via GetThreadContext).
-  GetThreadContext().SetCurrentTaskId(
+  GetThreadContext().SetCurrentTaskId((worker_type_ == WorkerType::DRIVER)
-      (worker_type_ == WorkerType::DRIVER) ? TaskID::FromRandom() : TaskID::Nil());
+                                          ? TaskID::ForDriverTask(job_id)
+                                          : TaskID::Nil());
 }
 
 const WorkerType WorkerContext::GetWorkerType() const { return worker_type_; }
@@ -76,7 +77,6 @@ void WorkerContext::SetCurrentTask(const TaskSpecification &task_spec) {
   current_job_id_ = task_spec.JobId();
   GetThreadContext().SetCurrentTask(task_spec);
 }
-
 std::shared_ptr<const TaskSpecification> WorkerContext::GetCurrentTask() const {
   return GetThreadContext().GetCurrentTask();
 }

src/ray/core_worker/object_interface.cc

@@ -17,7 +17,8 @@ CoreWorkerObjectInterface::CoreWorkerObjectInterface(
 
 Status CoreWorkerObjectInterface::Put(const RayObject &object, ObjectID *object_id) {
   ObjectID put_id = ObjectID::ForPut(worker_context_.GetCurrentTaskID(),
-                                     worker_context_.GetNextPutIndex());
+                                     worker_context_.GetNextPutIndex(),
+                                     /*transport_type=*/0);
   *object_id = put_id;
   return Put(object, put_id);
 }

src/ray/core_worker/task_interface.cc

@@ -17,7 +17,11 @@ ActorHandle::ActorHandle(
   *inner_.mutable_actor_creation_task_function_descriptor() = {
       actor_creation_task_function_descriptor.begin(),
       actor_creation_task_function_descriptor.end()};
-  inner_.set_actor_cursor(actor_id.Data(), actor_id.Size());
+  const auto &actor_creation_task_id = TaskID::ForActorCreationTask(actor_id);
+  const auto &actor_creation_dummy_object_id =
+      ObjectID::ForTaskReturn(actor_creation_task_id, /*index=*/1, /*transport_type=*/0);
+  inner_.set_actor_cursor(actor_creation_dummy_object_id.Data(),
+                          actor_creation_dummy_object_id.Size());
   inner_.set_is_direct_call(is_direct_call);
 }
 
@@ -109,17 +113,16 @@ CoreWorkerTaskInterface::CoreWorkerTaskInterface(
 }
 
 void CoreWorkerTaskInterface::BuildCommonTaskSpec(
-    TaskSpecBuilder &builder, const RayFunction &function,
+    TaskSpecBuilder &builder, const TaskID &task_id, const int task_index,
-    const std::vector<TaskArg> &args, uint64_t num_returns,
+    const RayFunction &function, const std::vector<TaskArg> &args, uint64_t num_returns,
     const std::unordered_map<std::string, double> &required_resources,
     const std::unordered_map<std::string, double> &required_placement_resources,
     std::vector<ObjectID> *return_ids) {
-  auto next_task_index = worker_context_.GetNextTaskIndex();
   // Build common task spec.
-  builder.SetCommonTaskSpec(
+  builder.SetCommonTaskSpec(task_id, function.language, function.function_descriptor,
-      function.language, function.function_descriptor, worker_context_.GetCurrentJobID(),
+                            worker_context_.GetCurrentJobID(),
-      worker_context_.GetCurrentTaskID(), next_task_index, num_returns,
+                            worker_context_.GetCurrentTaskID(), task_index, num_returns,
-      required_resources, required_placement_resources);
+                            required_resources, required_placement_resources);
   // Set task arguments.
   for (const auto &arg : args) {
     if (arg.IsPassedByReference()) {
@@ -130,10 +133,9 @@ void CoreWorkerTaskInterface::BuildCommonTaskSpec(
   }
 
   // Compute return IDs.
-  const auto task_id = TaskID::FromBinary(builder.GetMessage().task_id());
   (*return_ids).resize(num_returns);
   for (int i = 0; i < num_returns; i++) {
-    (*return_ids)[i] = ObjectID::ForTaskReturn(task_id, i + 1);
+    (*return_ids)[i] = ObjectID::ForTaskReturn(task_id, i + 1, /*transport_type=*/0);
   }
 }
 
@@ -142,8 +144,12 @@ Status CoreWorkerTaskInterface::SubmitTask(const RayFunction &function,
                                            const TaskOptions &task_options,
                                            std::vector<ObjectID> *return_ids) {
   TaskSpecBuilder builder;
-  BuildCommonTaskSpec(builder, function, args, task_options.num_returns,
+  const int next_task_index = worker_context_.GetNextTaskIndex();
-                      task_options.resources, {}, return_ids);
+  const auto task_id =
+      TaskID::ForNormalTask(worker_context_.GetCurrentJobID(),
+                            worker_context_.GetCurrentTaskID(), next_task_index);
+  BuildCommonTaskSpec(builder, task_id, next_task_index, function, args,
+                      task_options.num_returns, task_options.resources, {}, return_ids);
   return task_submitters_[TaskTransportType::RAYLET]->SubmitTask(builder.Build());
 }
 
@@ -151,12 +157,16 @@ Status CoreWorkerTaskInterface::CreateActor(
     const RayFunction &function, const std::vector<TaskArg> &args,
     const ActorCreationOptions &actor_creation_options,
     std::unique_ptr<ActorHandle> *actor_handle) {
+  const int next_task_index = worker_context_.GetNextTaskIndex();
+  const ActorID actor_id =
+      ActorID::Of(worker_context_.GetCurrentJobID(), worker_context_.GetCurrentTaskID(),
+                  next_task_index);
+  const TaskID actor_creation_task_id = TaskID::ForActorCreationTask(actor_id);
   std::vector<ObjectID> return_ids;
   TaskSpecBuilder builder;
-  BuildCommonTaskSpec(builder, function, args, 1, actor_creation_options.resources,
+  BuildCommonTaskSpec(builder, actor_creation_task_id, next_task_index, function, args, 1,
-                      actor_creation_options.resources, &return_ids);
+                      actor_creation_options.resources, actor_creation_options.resources,
-
+                      &return_ids);
-  const ActorID actor_id = ActorID::FromBinary(return_ids[0].Binary());
   builder.SetActorCreationTaskSpec(actor_id, actor_creation_options.max_reconstructions,
                                    {});
 
@@ -179,13 +189,19 @@ Status CoreWorkerTaskInterface::SubmitActorTask(ActorHandle &actor_handle,
 
   // Build common task spec.
   TaskSpecBuilder builder;
-  BuildCommonTaskSpec(builder, function, args, num_returns, task_options.resources, {},
+  const int next_task_index = worker_context_.GetNextTaskIndex();
-                      return_ids);
+  const auto actor_task_id = TaskID::ForActorTask(
+      worker_context_.GetCurrentJobID(), worker_context_.GetCurrentTaskID(),
+      next_task_index, actor_handle.ActorID());
+  BuildCommonTaskSpec(builder, actor_task_id, next_task_index, function, args,
+                      num_returns, task_options.resources, {}, return_ids);
 
   std::unique_lock<std::mutex> guard(actor_handle.mutex_);
   // Build actor task spec.
+  const auto actor_creation_task_id =
+      TaskID::ForActorCreationTask(actor_handle.ActorID());
   const auto actor_creation_dummy_object_id =
-      ObjectID::FromBinary(actor_handle.ActorID().Binary());
+      ObjectID::ForTaskReturn(actor_creation_task_id, /*index=*/1, /*transport_type=*/0);
   builder.SetActorTaskSpec(
       actor_handle.ActorID(), actor_handle.ActorHandleID(),
       actor_creation_dummy_object_id,

src/ray/core_worker/task_interface.h

@@ -170,6 +170,8 @@ class CoreWorkerTaskInterface {
   /// Build common attributes of the task spec, and compute return ids.
   ///
   /// \param[in] builder Builder to build a `TaskSpec`.
+  /// \param[in] task_id The ID of this task.
+  /// \param[in] task_index The task index used to build this task.
   /// \param[in] function The remote function to execute.
   /// \param[in] args Arguments of this task.
   /// \param[in] num_returns Number of returns.
@@ -179,8 +181,8 @@ class CoreWorkerTaskInterface {
   /// \param[out] return_ids Return IDs.
   /// \return Void.
   void BuildCommonTaskSpec(
-      TaskSpecBuilder &builder, const RayFunction &function,
+      TaskSpecBuilder &builder, const TaskID &task_id, const int task_index,
-      const std::vector<TaskArg> &args, uint64_t num_returns,
+      const RayFunction &function, const std::vector<TaskArg> &args, uint64_t num_returns,
       const std::unordered_map<std::string, double> &required_resources,
       const std::unordered_map<std::string, double> &required_placement_resources,
       std::vector<ObjectID> *return_ids);

src/ray/core_worker/test/core_worker_test.cc

@@ -21,6 +21,7 @@
 
 #include "ray/thirdparty/hiredis/async.h"
 #include "ray/thirdparty/hiredis/hiredis.h"
+#include "ray/util/test_util.h"
 
 namespace ray {
 
@@ -104,6 +105,11 @@ class CoreWorkerTest : public ::testing::Test {
     }
   }
 
+  JobID NextJobId() const {
+    static uint32_t job_counter = 1;
+    return JobID::FromInt(job_counter++);
+  }
+
   std::string StartStore() {
     std::string store_socket_name = "/tmp/store" + RandomObjectID().Hex();
     std::string store_pid = store_socket_name + ".pid";
@@ -213,7 +219,7 @@ bool CoreWorkerTest::WaitForDirectCallActorState(CoreWorker &worker,
 void CoreWorkerTest::TestNormalTask(
     const std::unordered_map<std::string, double> &resources) {
   CoreWorker driver(WorkerType::DRIVER, Language::PYTHON, raylet_store_socket_names_[0],
-                    raylet_socket_names_[0], JobID::FromInt(1), gcs_options_, nullptr);
+                    raylet_socket_names_[0], NextJobId(), gcs_options_, nullptr);
 
   // Test for tasks with by-value and by-ref args.
   {
@@ -254,7 +260,7 @@ void CoreWorkerTest::TestNormalTask(
 void CoreWorkerTest::TestActorTask(
     const std::unordered_map<std::string, double> &resources, bool is_direct_call) {
   CoreWorker driver(WorkerType::DRIVER, Language::PYTHON, raylet_store_socket_names_[0],
-                    raylet_socket_names_[0], JobID::FromInt(1), gcs_options_, nullptr);
+                    raylet_socket_names_[0], NextJobId(), gcs_options_, nullptr);
 
   auto actor_handle = CreateActorHelper(driver, resources, is_direct_call, 1000);
 
@@ -336,7 +342,7 @@ void CoreWorkerTest::TestActorTask(
 void CoreWorkerTest::TestActorReconstruction(
     const std::unordered_map<std::string, double> &resources, bool is_direct_call) {
   CoreWorker driver(WorkerType::DRIVER, Language::PYTHON, raylet_store_socket_names_[0],
-                    raylet_socket_names_[0], JobID::FromInt(1), gcs_options_, nullptr);
+                    raylet_socket_names_[0], NextJobId(), gcs_options_, nullptr);
 
   // creating actor.
   auto actor_handle = CreateActorHelper(driver, resources, is_direct_call, 1000);
@@ -393,7 +399,7 @@ void CoreWorkerTest::TestActorReconstruction(
 void CoreWorkerTest::TestActorFailure(
     const std::unordered_map<std::string, double> &resources, bool is_direct_call) {
   CoreWorker driver(WorkerType::DRIVER, Language::PYTHON, raylet_store_socket_names_[0],
-                    raylet_socket_names_[0], JobID::FromInt(1), gcs_options_, nullptr);
+                    raylet_socket_names_[0], NextJobId(), gcs_options_, nullptr);
 
   // creating actor.
   auto actor_handle =
@@ -499,13 +505,13 @@ void CoreWorkerTest::TestStoreProvider(StoreProviderType type) {
   wait_ids.push_back(non_existent_id);
 
   std::vector<bool> wait_results;
-  RAY_CHECK_OK(provider.Wait(wait_ids, 5, 100, TaskID::FromRandom(), &wait_results));
+  RAY_CHECK_OK(provider.Wait(wait_ids, 5, 100, RandomTaskId(), &wait_results));
   ASSERT_EQ(wait_results.size(), 5);
   ASSERT_EQ(wait_results, std::vector<bool>({true, true, true, true, false}));
 
   // Test Get().
   std::vector<std::shared_ptr<RayObject>> results;
-  RAY_CHECK_OK(provider.Get(ids_with_duplicate, -1, TaskID::FromRandom(), &results));
+  RAY_CHECK_OK(provider.Get(ids_with_duplicate, -1, RandomTaskId(), &results));
 
   ASSERT_EQ(results.size(), ids_with_duplicate.size());
   for (size_t i = 0; i < ids_with_duplicate.size(); i++) {
@@ -527,7 +533,7 @@ void CoreWorkerTest::TestStoreProvider(StoreProviderType type) {
   RAY_CHECK_OK(provider.Delete(ids, true, false));
 
   usleep(200 * 1000);
-  RAY_CHECK_OK(provider.Get(ids, 0, TaskID::FromRandom(), &results));
+  RAY_CHECK_OK(provider.Get(ids, 0, RandomTaskId(), &results));
   ASSERT_EQ(results.size(), 2);
   ASSERT_TRUE(!results[0]);
   ASSERT_TRUE(!results[1]);
@@ -576,9 +582,10 @@ TEST_F(ZeroNodeTest, TestTaskSpecPerf) {
 
   std::unordered_map<std::string, double> resources;
   ActorCreationOptions actor_options{0, /* is_direct_call */ true, resources};
-
+  const auto job_id = NextJobId();
-  ActorHandle actor_handle(ActorID::FromRandom(), ActorHandleID::Nil(), function.language,
+  ActorHandle actor_handle(ActorID::Of(job_id, TaskID::ForDriverTask(job_id), 1),
-                           true, function.function_descriptor);
+                           ActorHandleID::Nil(), function.language, true,
+                           function.function_descriptor);
 
   // Manually create `num_tasks` task specs, and for each of them create a
   // `PushTaskRequest`, this is to batch performance of TaskSpec
@@ -592,9 +599,9 @@ TEST_F(ZeroNodeTest, TestTaskSpecPerf) {
     auto num_returns = options.num_returns;
 
     TaskSpecBuilder builder;
-    builder.SetCommonTaskSpec(function.language, function.function_descriptor,
+    builder.SetCommonTaskSpec(RandomTaskId(), function.language,
-                              JobID::FromInt(1), TaskID::FromRandom(), 0, num_returns,
+                              function.function_descriptor, job_id, RandomTaskId(), 0,
-                              resources, resources);
+                              num_returns, resources, resources);
     // Set task arguments.
     for (const auto &arg : args) {
       if (arg.IsPassedByReference()) {
@@ -605,7 +612,8 @@ TEST_F(ZeroNodeTest, TestTaskSpecPerf) {
     }
 
     const auto actor_creation_dummy_object_id =
-        ObjectID::FromBinary(actor_handle.ActorID().Binary());
+        ObjectID::ForTaskReturn(TaskID::ForActorCreationTask(actor_handle.ActorID()),
+                                /*index=*/1, /*transport_type=*/0);
     builder.SetActorTaskSpec(
         actor_handle.ActorID(), actor_handle.ActorHandleID(),
         actor_creation_dummy_object_id,
@@ -624,27 +632,22 @@ TEST_F(ZeroNodeTest, TestTaskSpecPerf) {
 TEST_F(SingleNodeTest, TestDirectActorTaskSubmissionPerf) {
   CoreWorker driver(WorkerType::DRIVER, Language::PYTHON, raylet_store_socket_names_[0],
                     raylet_socket_names_[0], JobID::FromInt(1), gcs_options_, nullptr);
-
   std::unique_ptr<ActorHandle> actor_handle;
 
   // Test creating actor.
   uint8_t array[] = {1, 2, 3};
   auto buffer = std::make_shared<LocalMemoryBuffer>(array, sizeof(array));
-
   RayFunction func{ray::Language::PYTHON, {}};
   std::vector<TaskArg> args;
   args.emplace_back(TaskArg::PassByValue(buffer));
 
   std::unordered_map<std::string, double> resources;
   ActorCreationOptions actor_options{0, /* is_direct_call */ true, resources};
-
   // Create an actor.
   RAY_CHECK_OK(driver.Tasks().CreateActor(func, args, actor_options, &actor_handle));
-
   // wait for actor creation finish.
   ASSERT_TRUE(WaitForDirectCallActorState(driver, actor_handle->ActorID(), true,
                                           30 * 1000 /* 30s */));
-
   // Test submitting some tasks with by-value args for that actor.
   int64_t start_ms = current_time_ms();
   const int num_tasks = 10000;
@@ -667,7 +670,7 @@ TEST_F(SingleNodeTest, TestDirectActorTaskSubmissionPerf) {
 }
 
 TEST_F(ZeroNodeTest, TestWorkerContext) {
-  auto job_id = JobID::JobID::FromInt(1);
+  auto job_id = NextJobId();
 
   WorkerContext context(WorkerType::WORKER, job_id);
   ASSERT_TRUE(context.GetCurrentTaskID().IsNil());
@@ -692,8 +695,9 @@ TEST_F(ZeroNodeTest, TestWorkerContext) {
 }
 
 TEST_F(ZeroNodeTest, TestActorHandle) {
-  ActorHandle handle1(ActorID::FromRandom(), ActorHandleID::FromRandom(), Language::JAVA,
+  const auto job_id = NextJobId();
-                      false,
+  ActorHandle handle1(ActorID::Of(job_id, TaskID::ForDriverTask(job_id), 1),
+                      ActorHandleID::FromRandom(), Language::JAVA, false,
                       {"org.ray.exampleClass", "exampleMethod", "exampleSignature"});
 
   auto forkedHandle1 = handle1.Fork();
@@ -788,10 +792,10 @@ TEST_F(SingleNodeTest, TestObjectInterface) {
 
 TEST_F(TwoNodeTest, TestObjectInterfaceCrossNodes) {
   CoreWorker worker1(WorkerType::DRIVER, Language::PYTHON, raylet_store_socket_names_[0],
-                     raylet_socket_names_[0], JobID::FromInt(1), gcs_options_, nullptr);
+                     raylet_socket_names_[0], NextJobId(), gcs_options_, nullptr);
 
   CoreWorker worker2(WorkerType::DRIVER, Language::PYTHON, raylet_store_socket_names_[1],
-                     raylet_socket_names_[1], JobID::FromInt(1), gcs_options_, nullptr);
+                     raylet_socket_names_[1], NextJobId(), gcs_options_, nullptr);
 
   uint8_t array1[] = {1, 2, 3, 4, 5, 6, 7, 8};
   uint8_t array2[] = {10, 11, 12, 13, 14, 15};

src/ray/core_worker/transport/direct_actor_transport.cc

@@ -158,7 +158,8 @@ Status CoreWorkerDirectActorTaskSubmitter::PushTask(rpc::DirectActorClient &clie
 void CoreWorkerDirectActorTaskSubmitter::TreatTaskAsFailed(
     const TaskID &task_id, int num_returns, const rpc::ErrorType &error_type) {
   for (int i = 0; i < num_returns; i++) {
-    const auto object_id = ObjectID::ForTaskReturn(task_id, i + 1);
+    const auto object_id =
+        ObjectID::ForTaskReturn(task_id, /*index=*/i + 1, /*transport_type=*/0);
     std::string meta = std::to_string(static_cast<int>(error_type));
     auto metadata = const_cast<uint8_t *>(reinterpret_cast<const uint8_t *>(meta.data()));
     auto meta_buffer = std::make_shared<LocalMemoryBuffer>(metadata, meta.size());
@@ -204,7 +205,8 @@ void CoreWorkerDirectActorTaskReceiver::HandlePushTask(
 
   for (int i = 0; i < results.size(); i++) {
     auto return_object = (*reply).add_return_objects();
-    ObjectID id = ObjectID::ForTaskReturn(task_spec.TaskId(), i + 1);
+    ObjectID id = ObjectID::ForTaskReturn(task_spec.TaskId(), /*index=*/i + 1,
+                                          /*transport_type=*/0);
     return_object->set_object_id(id.Binary());
     const auto &result = results[i];
     if (result->GetData() != nullptr) {

src/ray/core_worker/transport/raylet_transport.cc

@@ -41,7 +41,8 @@ void CoreWorkerRayletTaskReceiver::HandleAssignTask(
 
   RAY_CHECK(results.size() == num_returns);
   for (int i = 0; i < num_returns; i++) {
-    ObjectID id = ObjectID::ForTaskReturn(task_spec.TaskId(), i + 1);
+    ObjectID id = ObjectID::ForTaskReturn(task_spec.TaskId(), /*index=*/i + 1,
+                                          /*transport_type=*/0);
     object_interface_.Put(*results[i], id);
   }
 

src/ray/design_docs/id_specification.md

@@ -0,0 +1,72 @@
+Ray ID Specification
+============================================
+```
+
+ high bits                                                                           low bits
+<--------------------------------------------------------------------------------------------
+
+                                                                                   4B
+                                                                          +-----------------+
+                                                                          |   unique bytes  |  JobID     4B
+                                                                          +-----------------+
+
+                                                                 4B                4B
+                                                        +-----------------+-----------------+
+                                                        |   unique bytes  |       JobID     |  ActorID   8B
+                                                        +-----------------+-----------------+
+
+                                        6B                               8B
+                            +---------------------------+-----------------------------------+
+                            |       unique bytes        |               ActorID             |  TaskID   14B
+                            +---------------------------+-----------------------------------+
+
+       4B            2B                                  14B
++---------------------------+---------------------------------------------------------------+
+|  index bytes  |flags bytes|                             TaskID                            |  ObjectID 20B
++---------------------------+---------------------------------------------------------------+
+
+```
+#### JobID (4 bytes)
+`JobID` is generated by `GCS` to ensure uniqueness. Its length is 4 bytes.
+
+#### ActorID (8 bytes)
+An `ActorID` contains two parts: 1) 4 unique bytes, and 2) its `JobID`.
+
+#### TaskID (14 bytes)
+A `TaskID` contains two parts: 1) 6 unique bytes, and 2) its `ActorID`.  
+If the task is a normal task or a driver task, the part 2 is its dummy actor id.
+
+The following table shows the layouts of all kinds of task id.
+```
++-------------------+-----------------+------------+---------------------------+-----------------+
+|                   | Normal Task     | Actor Task | Actor Creation Task       | Driver Task     |
++-------------------+-----------------+------------+---------------------------+-----------------+
+| task unique bytes | random          | random     | nil                       | nil             |
++-------------------+-----------------+------------+---------------------------+-----------------+
+| actor id          | dummy actor id* | actor id   | Id of the actor to create | dummy actor id* |
++-------------------+-----------------+------------+---------------------------+-----------------+
+Note: Dummy actor id is an `ActorID` whose unique part is nil.
+```
+
+#### ObjectID (20 bytes)
+An `ObjectID` contains 3 parts:
+- `index bytes`: 4 bytes to indicate the index of the object.
+- `flags bytes`: 2 bytes to indicate the flags of this object. We have 3 flags now: `created_by_task`, `object_type` and `transport_type`.
+- `TaskID`: 14 bytes to indicate the ID of the task to which this object belongs.
+
+**flags bytes format**
+```
+  1b     1b        3b                          11b
++-------------------------------------------------------------------------+
+| (1) | (2) |     (3)      |                (4)unused                     |
++-------------------------------------------------------------------------+
+```
+- The (1) `created_by_task` part is one bit to indicate whether this `ObjectID` is generated (put or returned) from a task.
+
+- The (2) `object_type` part is one bit to indicate the type of this object, whether a `PUT_OBJECT` or a `RETURN_OBJECT`.
+    - `PUT_OBJECT` indicates this object is generated through `ray.put` during the task's execution.
+    - `RETURN_OBJECT` indicates this object is the return value of a task.
+
+- The (3) `transport_type` part is 3 bits to indicate the type of the transport which is used to transfer this object. So it can support 8 types.
+
+- There are 11 bits unused in `flags bytes`.

src/ray/gcs/actor_state_accessor_test.cc

@@ -5,6 +5,7 @@
 #include <vector>
 #include "gtest/gtest.h"
 #include "ray/gcs/redis_gcs_client.h"
+#include "ray/util/test_util.h"
 
 namespace ray {
 
@@ -45,13 +46,13 @@ class ActorStateAccessorTest : public ::testing::Test {
   void GenActorData() {
     for (size_t i = 0; i < 2; ++i) {
       std::shared_ptr<ActorTableData> actor = std::make_shared<ActorTableData>();
-      ActorID actor_id = ActorID::FromRandom();
-      actor->set_actor_id(actor_id.Binary());
       actor->set_max_reconstructions(1);
       actor->set_remaining_reconstructions(1);
       JobID job_id = JobID::FromInt(i);
       actor->set_job_id(job_id.Binary());
       actor->set_state(ActorTableData::ALIVE);
+      ActorID actor_id = ActorID::Of(job_id, RandomTaskId(), /*parent_task_counter=*/i);
+      actor->set_actor_id(actor_id.Binary());
       actor_datas_[actor_id] = actor;
     }
   }

src/ray/gcs/redis_gcs_client_test.cc

@@ -8,6 +8,7 @@ extern "C" {
 #include "ray/common/ray_config.h"
 #include "ray/gcs/redis_gcs_client.h"
 #include "ray/gcs/tables.h"
+#include "ray/util/test_util.h"
 
 namespace ray {
 
@@ -104,7 +105,7 @@ bool TaskTableDataEqual(const TaskTableData &data1, const TaskTableData &data2)
 }
 
 void TestTableLookup(const JobID &job_id, std::shared_ptr<gcs::RedisGcsClient> client) {
-  const auto task_id = TaskID::FromRandom();
+  const auto task_id = RandomTaskId();
   const auto data = CreateTaskTableData(task_id);
 
   // Check that we added the correct task.
@@ -151,7 +152,7 @@ TEST_MACRO(TestGcsWithChainAsio, TestTableLookup);
 
 void TestLogLookup(const JobID &job_id, std::shared_ptr<gcs::RedisGcsClient> client) {
   // Append some entries to the log at an object ID.
-  TaskID task_id = TaskID::FromRandom();
+  TaskID task_id = RandomTaskId();
   std::vector<std::string> node_manager_ids = {"abc", "def", "ghi"};
   for (auto &node_manager_id : node_manager_ids) {
     auto data = std::make_shared<TaskReconstructionData>();
@@ -196,7 +197,7 @@ TEST_F(TestGcsWithAsio, TestLogLookup) {
 
 void TestTableLookupFailure(const JobID &job_id,
                             std::shared_ptr<gcs::RedisGcsClient> client) {
-  TaskID task_id = TaskID::FromRandom();
+  TaskID task_id = RandomTaskId();
 
   // Check that the lookup does not return data.
   auto lookup_callback = [](gcs::RedisGcsClient *client, const TaskID &id,
@@ -222,7 +223,7 @@ TEST_MACRO(TestGcsWithChainAsio, TestTableLookupFailure);
 #endif
 
 void TestLogAppendAt(const JobID &job_id, std::shared_ptr<gcs::RedisGcsClient> client) {
-  TaskID task_id = TaskID::FromRandom();
+  TaskID task_id = RandomTaskId();
   std::vector<std::string> node_manager_ids = {"A", "B"};
   std::vector<std::shared_ptr<TaskReconstructionData>> data_log;
   for (const auto &node_manager_id : node_manager_ids) {
@@ -352,7 +353,7 @@ void TestDeleteKeysFromLog(
   std::vector<TaskID> ids;
   TaskID task_id;
   for (auto &data : data_vector) {
-    task_id = TaskID::FromRandom();
+    task_id = RandomTaskId();
     ids.push_back(task_id);
     // Check that we added the correct object entries.
     auto add_callback = [task_id, data](gcs::RedisGcsClient *client, const TaskID &id,
@@ -400,7 +401,7 @@ void TestDeleteKeysFromTable(const JobID &job_id,
   std::vector<TaskID> ids;
   TaskID task_id;
   for (auto &data : data_vector) {
-    task_id = TaskID::FromRandom();
+    task_id = RandomTaskId();
     ids.push_back(task_id);
     // Check that we added the correct object entries.
     auto add_callback = [task_id, data](gcs::RedisGcsClient *client, const TaskID &id,
@@ -521,7 +522,7 @@ void TestDeleteKeys(const JobID &job_id, std::shared_ptr<gcs::RedisGcsClient> cl
   std::vector<std::shared_ptr<TaskTableData>> task_vector;
   auto AppendTaskData = [&task_vector](size_t add_count) {
     for (size_t i = 0; i < add_count; ++i) {
-      task_vector.push_back(CreateTaskTableData(TaskID::FromRandom()));
+      task_vector.push_back(CreateTaskTableData(RandomTaskId()));
     }
   };
   AppendTaskData(1);
@@ -703,10 +704,10 @@ void TestTableSubscribeId(const JobID &job_id,
   int num_modifications = 3;
 
   // Add a table entry.
-  TaskID task_id1 = TaskID::FromRandom();
+  TaskID task_id1 = RandomTaskId();
 
   // Add a table entry at a second key.
-  TaskID task_id2 = TaskID::FromRandom();
+  TaskID task_id2 = RandomTaskId();
 
   // The callback for a notification from the table. This should only be
   // received for keys that we requested notifications for.
@@ -927,7 +928,7 @@ TEST_F(TestGcsWithAsio, TestSetSubscribeId) {
 void TestTableSubscribeCancel(const JobID &job_id,
                               std::shared_ptr<gcs::RedisGcsClient> client) {
   // Add a table entry.
-  const auto task_id = TaskID::FromRandom();
+  const auto task_id = RandomTaskId();
   const int num_modifications = 3;
   const auto data = CreateTaskTableData(task_id, 0);
   RAY_CHECK_OK(client->raylet_task_table().Add(job_id, task_id, data, nullptr));

src/ray/gcs/tables.cc

@@ -685,7 +685,7 @@ Status ActorCheckpointIdTable::AddCheckpointId(const JobID &job_id,
                                                const ActorID &actor_id,
                                                const ActorCheckpointID &checkpoint_id) {
   auto lookup_callback = [this, checkpoint_id, job_id, actor_id](
-                             ray::gcs::RedisGcsClient *client, const UniqueID &id,
+                             ray::gcs::RedisGcsClient *client, const ActorID &id,
                              const ActorCheckpointIdData &data) {
     std::shared_ptr<ActorCheckpointIdData> copy =
         std::make_shared<ActorCheckpointIdData>(data);
@@ -695,7 +695,6 @@ Status ActorCheckpointIdTable::AddCheckpointId(const JobID &job_id,
     while (copy->timestamps().size() > num_to_keep) {
       // Delete the checkpoint from actor checkpoint table.
       const auto &to_delete = ActorCheckpointID::FromBinary(copy->checkpoint_ids(0));
-      RAY_LOG(DEBUG) << "Deleting checkpoint " << to_delete << " for actor " << actor_id;
       copy->mutable_checkpoint_ids()->erase(copy->mutable_checkpoint_ids()->begin());
       copy->mutable_timestamps()->erase(copy->mutable_timestamps()->begin());
       client_->actor_checkpoint_table().Delete(job_id, to_delete);
@@ -703,7 +702,7 @@ Status ActorCheckpointIdTable::AddCheckpointId(const JobID &job_id,
     RAY_CHECK_OK(Add(job_id, actor_id, copy, nullptr));
   };
   auto failure_callback = [this, checkpoint_id, job_id, actor_id](
-                              ray::gcs::RedisGcsClient *client, const UniqueID &id) {
+                              ray::gcs::RedisGcsClient *client, const ActorID &id) {
     std::shared_ptr<ActorCheckpointIdData> data =
         std::make_shared<ActorCheckpointIdData>();
     data->set_actor_id(id.Binary());

src/ray/object_manager/object_manager.cc

@@ -61,7 +61,7 @@ void ObjectManager::StopRpcService() {
 void ObjectManager::HandleObjectAdded(
     const object_manager::protocol::ObjectInfoT &object_info) {
   // Notify the object directory that the object has been added to this node.
-  ObjectID object_id = ObjectID::FromBinary(object_info.object_id);
+  ObjectID object_id = ObjectID::FromPlasmaIdBinary(object_info.object_id);
   RAY_LOG(DEBUG) << "Object added " << object_id;
   RAY_CHECK(local_objects_.count(object_id) == 0);
   local_objects_[object_id].object_info = object_info;

src/ray/object_manager/object_store_notification_manager.cc

@@ -63,7 +63,8 @@ void ObjectStoreNotificationManager::ProcessStoreNotification(
 
   const auto &object_info =
       flatbuffers::GetRoot<object_manager::protocol::ObjectInfo>(notification_.data());
-  const auto &object_id = from_flatbuf<ObjectID>(*object_info->object_id());
+  const ObjectID object_id =
+      ObjectID::FromPlasmaIdBinary(object_info->object_id()->str());
   if (object_info->is_deletion()) {
     ProcessStoreRemove(object_id);
   } else {

src/ray/raylet/lib/java/org_ray_runtime_raylet_RayletClientImpl.cc

@@ -147,24 +147,71 @@ Java_org_ray_runtime_raylet_RayletClientImpl_nativeWaitObject(
 
 /*
  * Class:     org_ray_runtime_raylet_RayletClientImpl
- * Method:    nativeGenerateTaskId
+ * Method:    nativeGenerateActorCreationTaskId
  * Signature: ([B[BI)[B
  */
 JNIEXPORT jbyteArray JNICALL
-Java_org_ray_runtime_raylet_RayletClientImpl_nativeGenerateTaskId(
+Java_org_ray_runtime_raylet_RayletClientImpl_nativeGenerateActorCreationTaskId(
     JNIEnv *env, jclass, jbyteArray jobId, jbyteArray parentTaskId,
     jint parent_task_counter) {
   const auto job_id = JavaByteArrayToId<JobID>(env, jobId);
   const auto parent_task_id = JavaByteArrayToId<TaskID>(env, parentTaskId);
 
-  TaskID task_id = ray::GenerateTaskId(job_id, parent_task_id, parent_task_counter);
+  const ActorID actor_id = ray::ActorID::Of(job_id, parent_task_id, parent_task_counter);
+  const TaskID actor_creation_task_id = ray::TaskID::ForActorCreationTask(actor_id);
+  jbyteArray result = env->NewByteArray(actor_creation_task_id.Size());
+  if (nullptr == result) {
+    return nullptr;
+  }
+  env->SetByteArrayRegion(result, 0, actor_creation_task_id.Size(),
+                          reinterpret_cast<const jbyte *>(actor_creation_task_id.Data()));
+  return result;
+}
+
+/*
+ * Class:     org_ray_runtime_raylet_RayletClientImpl
+ * Method:    nativeGenerateActorTaskId
+ * Signature: ([B[BI[B)[B
+ */
+JNIEXPORT jbyteArray JNICALL
+Java_org_ray_runtime_raylet_RayletClientImpl_nativeGenerateActorTaskId(
+    JNIEnv *env, jclass, jbyteArray jobId, jbyteArray parentTaskId,
+    jint parent_task_counter, jbyteArray actorId) {
+  const auto job_id = JavaByteArrayToId<JobID>(env, jobId);
+  const auto parent_task_id = JavaByteArrayToId<TaskID>(env, parentTaskId);
+  const auto actor_id = JavaByteArrayToId<ActorID>(env, actorId);
+  const TaskID actor_task_id =
+      ray::TaskID::ForActorTask(job_id, parent_task_id, parent_task_counter, actor_id);
+
+  jbyteArray result = env->NewByteArray(actor_task_id.Size());
+  if (nullptr == result) {
+    return nullptr;
+  }
+  env->SetByteArrayRegion(result, 0, actor_task_id.Size(),
+                          reinterpret_cast<const jbyte *>(actor_task_id.Data()));
+  return result;
+}
+
+/*
+ * Class:     org_ray_runtime_raylet_RayletClientImpl
+ * Method:    nativeGenerateNormalTaskId
+ * Signature: ([B[BI)[B
+ */
+JNIEXPORT jbyteArray JNICALL
+Java_org_ray_runtime_raylet_RayletClientImpl_nativeGenerateNormalTaskId(
+    JNIEnv *env, jclass, jbyteArray jobId, jbyteArray parentTaskId,
+    jint parent_task_counter) {
+  const auto job_id = JavaByteArrayToId<JobID>(env, jobId);
+  const auto parent_task_id = JavaByteArrayToId<TaskID>(env, parentTaskId);
+  const TaskID task_id =
+      ray::TaskID::ForNormalTask(job_id, parent_task_id, parent_task_counter);
+
   jbyteArray result = env->NewByteArray(task_id.Size());
   if (nullptr == result) {
     return nullptr;
   }
   env->SetByteArrayRegion(result, 0, task_id.Size(),
                           reinterpret_cast<const jbyte *>(task_id.Data()));
-
   return result;
 }
 

src/ray/raylet/lib/java/org_ray_runtime_raylet_RayletClientImpl.h

@@ -51,13 +51,33 @@ Java_org_ray_runtime_raylet_RayletClientImpl_nativeWaitObject(JNIEnv *, jclass,
 
 /*
  * Class:     org_ray_runtime_raylet_RayletClientImpl
- * Method:    nativeGenerateTaskId
+ * Method:    nativeGenerateActorCreationTaskId
  * Signature: ([B[BI)[B
  */
 JNIEXPORT jbyteArray JNICALL
-Java_org_ray_runtime_raylet_RayletClientImpl_nativeGenerateTaskId(JNIEnv *, jclass,
+Java_org_ray_runtime_raylet_RayletClientImpl_nativeGenerateActorCreationTaskId(
-                                                                  jbyteArray, jbyteArray,
+    JNIEnv *, jclass, jbyteArray, jbyteArray, jint);
-                                                                  jint);
+
+/*
+ * Class:     org_ray_runtime_raylet_RayletClientImpl
+ * Method:    nativeGenerateActorTaskId
+ * Signature: ([B[BI[B)[B
+ */
+JNIEXPORT jbyteArray JNICALL
+Java_org_ray_runtime_raylet_RayletClientImpl_nativeGenerateActorTaskId(JNIEnv *, jclass,
+                                                                       jbyteArray,
+                                                                       jbyteArray, jint,
+                                                                       jbyteArray);
+
+/*
+ * Class:     org_ray_runtime_raylet_RayletClientImpl
+ * Method:    nativeGenerateNormalTaskId
+ * Signature: ([B[BI)[B
+ */
+JNIEXPORT jbyteArray JNICALL
+Java_org_ray_runtime_raylet_RayletClientImpl_nativeGenerateNormalTaskId(JNIEnv *, jclass,
+                                                                        jbyteArray,
+                                                                        jbyteArray, jint);
 
 /*
  * Class:     org_ray_runtime_raylet_RayletClientImpl

src/ray/raylet/lineage_cache_test.cc

@@ -8,11 +8,16 @@
 #include "ray/common/task/task_spec.h"
 #include "ray/common/task/task_util.h"
 #include "ray/raylet/lineage_cache.h"
+#include "ray/util/test_util.h"
 
 namespace ray {
 
 namespace raylet {
 
+const static JobID kDefaultJobId = JobID::FromInt(1);
+
+const static TaskID kDefaultDriverTaskId = TaskID::ForDriverTask(kDefaultJobId);
+
 class MockGcs : public gcs::TableInterface<TaskID, TaskTableData>,
                 public gcs::PubsubInterface<TaskID> {
  public:
@@ -127,8 +132,8 @@ class LineageCacheTest : public ::testing::Test {
 static inline Task ExampleTask(const std::vector<ObjectID> &arguments,
                                uint64_t num_returns) {
   TaskSpecBuilder builder;
-  builder.SetCommonTaskSpec(Language::PYTHON, {"", "", ""}, JobID::Nil(),
+  builder.SetCommonTaskSpec(RandomTaskId(), Language::PYTHON, {"", "", ""}, JobID::Nil(),
-                            TaskID::FromRandom(), 0, num_returns, {}, {});
+                            RandomTaskId(), 0, num_returns, {}, {});
   for (const auto &arg : arguments) {
     builder.AddByRefArg(arg);
   }

src/ray/raylet/node_manager.cc

@@ -129,7 +129,7 @@ NodeManager::NodeManager(boost::asio::io_service &io_service,
 
   RAY_CHECK_OK(object_manager_.SubscribeObjAdded(
       [this](const object_manager::protocol::ObjectInfoT &object_info) {
-        ObjectID object_id = ObjectID::FromBinary(object_info.object_id);
+        ObjectID object_id = ObjectID::FromPlasmaIdBinary(object_info.object_id);
         HandleObjectLocal(object_id);
       }));
   RAY_CHECK_OK(object_manager_.SubscribeObjDeleted(

src/ray/raylet/reconstruction_policy_test.cc

@@ -15,6 +15,15 @@ namespace raylet {
 
 using rpc::TaskLeaseData;
 
+// A helper function to get a normal task id.
+inline TaskID ForNormalTask() {
+  const static JobID job_id = JobID::FromInt(1);
+  const static TaskID driver_task_id = TaskID::ForDriverTask(job_id);
+  static TaskID task_id =
+      TaskID::ForNormalTask(job_id, driver_task_id, /*parent_task_counter=*/1);
+  return task_id;
+}
+
 class MockObjectDirectory : public ObjectDirectoryInterface {
  public:
   MockObjectDirectory() {}
@@ -226,8 +235,9 @@ class ReconstructionPolicyTest : public ::testing::Test {
 };
 
 TEST_F(ReconstructionPolicyTest, TestReconstructionSimple) {
-  TaskID task_id = TaskID::FromRandom();
+  TaskID task_id = ForNormalTask();
-  ObjectID object_id = ObjectID::ForTaskReturn(task_id, 1);
+  ObjectID object_id =
+      ObjectID::ForTaskReturn(task_id, /*index=*/1, /*transport_type=*/0);
 
   // Listen for an object.
   reconstruction_policy_->ListenAndMaybeReconstruct(object_id);
@@ -244,8 +254,9 @@ TEST_F(ReconstructionPolicyTest, TestReconstructionSimple) {
 }
 
 TEST_F(ReconstructionPolicyTest, TestReconstructionEvicted) {
-  TaskID task_id = TaskID::FromRandom();
+  TaskID task_id = ForNormalTask();
-  ObjectID object_id = ObjectID::ForTaskReturn(task_id, 1);
+  ObjectID object_id =
+      ObjectID::ForTaskReturn(task_id, /*index=*/1, /*transport_type=*/0);
   mock_object_directory_->SetObjectLocations(object_id, {ClientID::FromRandom()});
 
   // Listen for both objects.
@@ -267,8 +278,9 @@ TEST_F(ReconstructionPolicyTest, TestReconstructionEvicted) {
 }
 
 TEST_F(ReconstructionPolicyTest, TestReconstructionObjectLost) {
-  TaskID task_id = TaskID::FromRandom();
+  TaskID task_id = ForNormalTask();
-  ObjectID object_id = ObjectID::ForTaskReturn(task_id, 1);
+  ObjectID object_id =
+      ObjectID::ForTaskReturn(task_id, /*index=*/1, /*transport_type=*/0);
   ClientID client_id = ClientID::FromRandom();
   mock_object_directory_->SetObjectLocations(object_id, {client_id});
 
@@ -291,9 +303,11 @@ TEST_F(ReconstructionPolicyTest, TestReconstructionObjectLost) {
 
 TEST_F(ReconstructionPolicyTest, TestDuplicateReconstruction) {
   // Create two object IDs produced by the same task.
-  TaskID task_id = TaskID::FromRandom();
+  TaskID task_id = ForNormalTask();
-  ObjectID object_id1 = ObjectID::ForTaskReturn(task_id, 1);
+  ObjectID object_id1 =
-  ObjectID object_id2 = ObjectID::ForTaskReturn(task_id, 2);
+      ObjectID::ForTaskReturn(task_id, /*index=*/1, /*transport_type=*/0);
+  ObjectID object_id2 =
+      ObjectID::ForTaskReturn(task_id, /*index=*/2, /*transport_type=*/0);
 
   // Listen for both objects.
   reconstruction_policy_->ListenAndMaybeReconstruct(object_id1);
@@ -311,8 +325,9 @@ TEST_F(ReconstructionPolicyTest, TestDuplicateReconstruction) {
 }
 
 TEST_F(ReconstructionPolicyTest, TestReconstructionSuppressed) {
-  TaskID task_id = TaskID::FromRandom();
+  TaskID task_id = ForNormalTask();
-  ObjectID object_id = ObjectID::ForTaskReturn(task_id, 1);
+  ObjectID object_id =
+      ObjectID::ForTaskReturn(task_id, /*index=*/1, /*transport_type=*/0);
   // Run the test for much longer than the reconstruction timeout.
   int64_t test_period = 2 * reconstruction_timeout_ms_;
 
@@ -337,8 +352,9 @@ TEST_F(ReconstructionPolicyTest, TestReconstructionSuppressed) {
 }
 
 TEST_F(ReconstructionPolicyTest, TestReconstructionContinuallySuppressed) {
-  TaskID task_id = TaskID::FromRandom();
+  TaskID task_id = ForNormalTask();
-  ObjectID object_id = ObjectID::ForTaskReturn(task_id, 1);
+  ObjectID object_id =
+      ObjectID::ForTaskReturn(task_id, /*index=*/1, /*transport_type=*/0);
 
   // Listen for an object.
   reconstruction_policy_->ListenAndMaybeReconstruct(object_id);
@@ -364,8 +380,9 @@ TEST_F(ReconstructionPolicyTest, TestReconstructionContinuallySuppressed) {
 }
 
 TEST_F(ReconstructionPolicyTest, TestReconstructionCanceled) {
-  TaskID task_id = TaskID::FromRandom();
+  TaskID task_id = ForNormalTask();
-  ObjectID object_id = ObjectID::ForTaskReturn(task_id, 1);
+  ObjectID object_id =
+      ObjectID::ForTaskReturn(task_id, /*index=*/1, /*transport_type=*/0);
 
   // Listen for an object.
   reconstruction_policy_->ListenAndMaybeReconstruct(object_id);
@@ -390,8 +407,9 @@ TEST_F(ReconstructionPolicyTest, TestReconstructionCanceled) {
 }
 
 TEST_F(ReconstructionPolicyTest, TestSimultaneousReconstructionSuppressed) {
-  TaskID task_id = TaskID::FromRandom();
+  TaskID task_id = ForNormalTask();
-  ObjectID object_id = ObjectID::ForTaskReturn(task_id, 1);
+  ObjectID object_id =
+      ObjectID::ForTaskReturn(task_id, /*index=*/1, /*transport_type=*/0);
 
   // Log a reconstruction attempt to simulate a different node attempting the
   // reconstruction first. This should suppress this node's first attempt at

src/ray/raylet/task_dependency_manager.cc

@@ -204,6 +204,8 @@ void TaskDependencyManager::SubscribeWaitDependencies(
       auto inserted = worker_entry.insert(object_id);
       if (inserted.second) {
         // Get the ID of the task that creates the dependency.
+        // TODO(qwang): Refine here to:
+        // if (object_id.CreatedByTask()) {// ...}
         TaskID creating_task_id = object_id.TaskId();
         // Add the subscribed worker to the mapping from object ID to list of
         // dependent workers.

src/ray/raylet/task_dependency_manager_test.cc

@@ -7,6 +7,7 @@
 
 #include "ray/common/task/task_util.h"
 #include "ray/raylet/task_dependency_manager.h"
+#include "ray/util/test_util.h"
 
 namespace ray {
 
@@ -14,6 +15,10 @@ namespace raylet {
 
 using ::testing::_;
 
+const static JobID kDefaultJobId = JobID::FromInt(1);
+
+const static TaskID kDefaultDriverTaskId = TaskID::ForDriverTask(kDefaultJobId);
+
 class MockObjectManager : public ObjectManagerInterface {
  public:
   MOCK_METHOD1(Pull, ray::Status(const ObjectID &object_id));
@@ -70,8 +75,8 @@ class TaskDependencyManagerTest : public ::testing::Test {
 static inline Task ExampleTask(const std::vector<ObjectID> &arguments,
                                uint64_t num_returns) {
   TaskSpecBuilder builder;
-  builder.SetCommonTaskSpec(Language::PYTHON, {"", "", ""}, JobID::Nil(),
+  builder.SetCommonTaskSpec(RandomTaskId(), Language::PYTHON, {"", "", ""}, JobID::Nil(),
-                            TaskID::FromRandom(), 0, num_returns, {}, {});
+                            RandomTaskId(), 0, num_returns, {}, {});
   for (const auto &arg : arguments) {
     builder.AddByRefArg(arg);
   }
@@ -103,7 +108,7 @@ TEST_F(TaskDependencyManagerTest, TestSimpleTask) {
   for (int i = 0; i < num_arguments; i++) {
     arguments.push_back(ObjectID::FromRandom());
   }
-  TaskID task_id = TaskID::FromRandom();
+  TaskID task_id = RandomTaskId();
   // No objects have been registered in the task dependency manager, so all
   // arguments should be remote.
   for (const auto &argument_id : arguments) {
@@ -135,7 +140,7 @@ TEST_F(TaskDependencyManagerTest, TestSimpleTask) {
 
 TEST_F(TaskDependencyManagerTest, TestDuplicateSubscribeGetDependencies) {
   // Create a task with 3 arguments.
-  TaskID task_id = TaskID::FromRandom();
+  TaskID task_id = RandomTaskId();
   int num_arguments = 3;
   std::vector<ObjectID> arguments;
   for (int i = 0; i < num_arguments; i++) {
@@ -180,7 +185,7 @@ TEST_F(TaskDependencyManagerTest, TestMultipleTasks) {
   EXPECT_CALL(object_manager_mock_, Pull(argument_id));
   EXPECT_CALL(reconstruction_policy_mock_, ListenAndMaybeReconstruct(argument_id));
   for (int i = 0; i < num_dependent_tasks; i++) {
-    TaskID task_id = TaskID::FromRandom();
+    TaskID task_id = RandomTaskId();
     dependent_tasks.push_back(task_id);
     // Subscribe to each of the task's dependencies.
     bool ready =
@@ -263,7 +268,8 @@ TEST_F(TaskDependencyManagerTest, TestTaskChain) {
 TEST_F(TaskDependencyManagerTest, TestDependentPut) {
   // Create a task with 3 arguments.
   auto task1 = ExampleTask({}, 0);
-  ObjectID put_id = ObjectID::ForPut(task1.GetTaskSpecification().TaskId(), 1);
+  ObjectID put_id = ObjectID::ForPut(task1.GetTaskSpecification().TaskId(), /*index=*/1,
+                                     /*transport_type=*/0);
   auto task2 = ExampleTask({put_id}, 0);
 
   // No objects have been registered in the task dependency manager, so the put
@@ -325,7 +331,7 @@ TEST_F(TaskDependencyManagerTest, TestEviction) {
   for (int i = 0; i < num_arguments; i++) {
     arguments.push_back(ObjectID::FromRandom());
   }
-  TaskID task_id = TaskID::FromRandom();
+  TaskID task_id = RandomTaskId();
   // No objects have been registered in the task dependency manager, so all
   // arguments should be remote.
   for (const auto &argument_id : arguments) {

src/ray/raylet/worker_pool_test.cc

@@ -186,7 +186,8 @@ TEST_F(WorkerPoolTest, PopActorWorker) {
   // Assign an actor ID to the worker.
   const auto task_spec = ExampleTaskSpec();
   auto actor = worker_pool_.PopWorker(task_spec);
-  auto actor_id = ActorID::FromRandom();
+  const auto job_id = JobID::FromInt(1);
+  auto actor_id = ActorID::Of(job_id, TaskID::ForDriverTask(job_id), 1);
   actor->AssignActorId(actor_id);
   worker_pool_.PushWorker(actor);
 
@@ -223,8 +224,10 @@ TEST_F(WorkerPoolTest, StartWorkerWithDynamicOptionsCommand) {
   SetWorkerCommands({{Language::PYTHON, {"dummy_py_worker_command"}},
                      {Language::JAVA, java_worker_command}});
 
+  const auto job_id = JobID::FromInt(1);
   TaskSpecification task_spec = ExampleTaskSpec(
-      ActorID::Nil(), Language::JAVA, ActorID::FromRandom(), {"test_op_0", "test_op_1"});
+      ActorID::Nil(), Language::JAVA,
+      ActorID::Of(job_id, TaskID::ForDriverTask(job_id), 1), {"test_op_0", "test_op_1"});
   worker_pool_.StartWorkerProcess(Language::JAVA, task_spec.DynamicWorkerOptions());
   const auto real_command =
       worker_pool_.GetWorkerCommand(worker_pool_.LastStartedWorkerProcess());

src/ray/util/test_util.h

@@ -3,6 +3,8 @@
 
 #include <string>
 
+#include "ray/util/util.h"
+
 namespace ray {
 
 /// Wait until the condition is met, or timeout is reached.
@@ -28,6 +30,13 @@ bool WaitForCondition(std::function<bool()> condition, int timeout_ms) {
   return false;
 }
 
+// A helper function to return a random task id.
+inline TaskID RandomTaskId() {
+  std::string data(TaskID::Size(), 0);
+  FillRandom(&data);
+  return TaskID::FromBinary(data);
+}
+
 }  // namespace ray
 
 #endif  // RAY_UTIL_TEST_UTIL_H

src/ray/util/util.h

@@ -4,7 +4,10 @@
 #include <boost/system/error_code.hpp>
 #include <chrono>
 #include <iterator>
+#include <mutex>
+#include <random>
 #include <sstream>
+#include <string>
 #include <unordered_map>
 
 #include "ray/common/status.h"
@@ -100,8 +103,30 @@ struct EnumClassHash {
   }
 };
 
-/// unodered_map for enum class type.
+/// unordered_map for enum class type.
 template <typename Key, typename T>
 using EnumUnorderedMap = std::unordered_map<Key, T, EnumClassHash>;
 
+/// A helper function to fill random bytes into the `data`.
+template <typename T>
+void FillRandom(T *data) {
+  RAY_CHECK(data != nullptr);
+  auto randomly_seeded_mersenne_twister = []() {
+    auto seed = std::chrono::high_resolution_clock::now().time_since_epoch().count();
+    std::mt19937 seeded_engine(seed);
+    return seeded_engine;
+  };
+
+  // NOTE(pcm): The right way to do this is to have one std::mt19937 per
+  // thread (using the thread_local keyword), but that's not supported on
+  // older versions of macOS (see https://stackoverflow.com/a/29929949)
+  static std::mutex random_engine_mutex;
+  std::lock_guard<std::mutex> lock(random_engine_mutex);
+  static std::mt19937 generator = randomly_seeded_mersenne_twister();
+  std::uniform_int_distribution<uint32_t> dist(0, std::numeric_limits<uint8_t>::max());
+  for (int i = 0; i < data->size(); i++) {
+    (*data)[i] = static_cast<uint8_t>(dist(generator));
+  }
+}
+
 #endif  // RAY_UTIL_UTIL_H