diff --git a/java/api/src/main/java/org/ray/api/Ray.java b/java/api/src/main/java/org/ray/api/Ray.java
index cdad95e16..4cf4ffac6 100644
--- a/java/api/src/main/java/org/ray/api/Ray.java
+++ b/java/api/src/main/java/org/ray/api/Ray.java
@@ -1,6 +1,7 @@
 package org.ray.api;
 
 import java.util.List;
+import java.util.concurrent.Callable;
 import org.ray.api.id.ObjectId;
 import org.ray.api.id.UniqueId;
 import org.ray.api.runtime.RayRuntime;
@@ -117,6 +118,28 @@ public final class Ray extends RayCall {
     return runtime.wait(waitList, waitList.size(), Integer.MAX_VALUE);
   }
 
+  /**
+   * If users want to use Ray API in there own threads, they should wrap their {@link Runnable}
+   * objects with this method.
+   *
+   * @param runnable The runnable to wrap.
+   * @return The wrapped runnable.
+   */
+  public static Runnable wrapRunnable(Runnable runnable) {
+    return runtime.wrapRunnable(runnable);
+  }
+
+  /**
+   * If users want to use Ray API in there own threads, they should wrap their {@link Callable}
+   * objects with this method.
+   *
+   * @param callable The callable to wrap.
+   * @return The wrapped callable.
+   */
+  public static Callable wrapCallable(Callable callable) {
+    return runtime.wrapCallable(callable);
+  }
+
   /**
    * Get the underlying runtime instance.
    */
diff --git a/java/api/src/main/java/org/ray/api/options/ActorCreationOptions.java b/java/api/src/main/java/org/ray/api/options/ActorCreationOptions.java
index 2e14ca858..928df3221 100644
--- a/java/api/src/main/java/org/ray/api/options/ActorCreationOptions.java
+++ b/java/api/src/main/java/org/ray/api/options/ActorCreationOptions.java
@@ -30,7 +30,7 @@ public class ActorCreationOptions extends BaseTaskOptions {
 
     private Map<String, Double> resources = new HashMap<>();
     private int maxReconstructions = NO_RECONSTRUCTION;
-    private String jvmOptions = "";
+    private String jvmOptions = null;
 
     public Builder setResources(Map<String, Double> resources) {
       this.resources = resources;
diff --git a/java/api/src/main/java/org/ray/api/runtime/RayRuntime.java b/java/api/src/main/java/org/ray/api/runtime/RayRuntime.java
index 5a29c9a39..46d5ca842 100644
--- a/java/api/src/main/java/org/ray/api/runtime/RayRuntime.java
+++ b/java/api/src/main/java/org/ray/api/runtime/RayRuntime.java
@@ -1,6 +1,7 @@
 package org.ray.api.runtime;
 
 import java.util.List;
+import java.util.concurrent.Callable;
 import org.ray.api.RayActor;
 import org.ray.api.RayObject;
 import org.ray.api.RayPyActor;
@@ -141,4 +142,18 @@ public interface RayRuntime {
    */
   RayPyActor createPyActor(String moduleName, String className, Object[] args,
       ActorCreationOptions options);
+
+  /**
+   * Wrap a {@link Runnable} with necessary context capture.
+   * @param runnable The runnable to wrap.
+   * @return The wrapped runnable.
+   */
+  Runnable wrapRunnable(Runnable runnable);
+
+  /**
+   * Wrap a {@link Callable} with necessary context capture.
+   * @param callable The callable to wrap.
+   * @return The wrapped callable.
+   */
+  Callable wrapCallable(Callable callable);
 }
diff --git a/java/runtime/src/main/java/org/ray/runtime/AbstractRayRuntime.java b/java/runtime/src/main/java/org/ray/runtime/AbstractRayRuntime.java
index e3132aa29..b3ea54e3f 100644
--- a/java/runtime/src/main/java/org/ray/runtime/AbstractRayRuntime.java
+++ b/java/runtime/src/main/java/org/ray/runtime/AbstractRayRuntime.java
@@ -4,6 +4,7 @@ import com.google.common.base.Preconditions;
 import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableList;
 import java.util.List;
+import java.util.concurrent.Callable;
 import org.ray.api.RayActor;
 import org.ray.api.RayObject;
 import org.ray.api.RayPyActor;
@@ -59,11 +60,6 @@ public abstract class AbstractRayRuntime implements RayRuntime {
     runtimeContext = new RuntimeContextImpl(this);
   }
 
-  /**
-   * Start runtime.
-   */
-  public abstract void start() throws Exception;
-
   @Override
   public abstract void shutdown();
 
@@ -168,6 +164,16 @@ public abstract class AbstractRayRuntime implements RayRuntime {
     return (RayPyActor) createActorImpl(functionDescriptor, args, options);
   }
 
+  @Override
+  public Runnable wrapRunnable(Runnable runnable) {
+    return runnable;
+  }
+
+  @Override
+  public Callable wrapCallable(Callable callable) {
+    return callable;
+  }
+
   private RayObject callNormalFunction(FunctionDescriptor functionDescriptor,
       Object[] args, int numReturns, CallOptions options) {
     List<FunctionArg> functionArgs = ArgumentsBuilder
diff --git a/java/runtime/src/main/java/org/ray/runtime/DefaultRayRuntimeFactory.java b/java/runtime/src/main/java/org/ray/runtime/DefaultRayRuntimeFactory.java
index 7223fa28e..f95d7cfa4 100644
--- a/java/runtime/src/main/java/org/ray/runtime/DefaultRayRuntimeFactory.java
+++ b/java/runtime/src/main/java/org/ray/runtime/DefaultRayRuntimeFactory.java
@@ -4,11 +4,12 @@ import org.ray.api.runtime.RayRuntime;
 import org.ray.api.runtime.RayRuntimeFactory;
 import org.ray.runtime.config.RayConfig;
 import org.ray.runtime.config.RunMode;
+import org.ray.runtime.generated.Common.WorkerType;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 /**
- * The default Ray runtime factory. It produces an instance of AbstractRayRuntime.
+ * The default Ray runtime factory. It produces an instance of RayRuntime.
  */
 public class DefaultRayRuntimeFactory implements RayRuntimeFactory {
 
@@ -18,14 +19,16 @@ public class DefaultRayRuntimeFactory implements RayRuntimeFactory {
   public RayRuntime createRayRuntime() {
     RayConfig rayConfig = RayConfig.create();
     try {
-      AbstractRayRuntime runtime;
+      RayRuntime runtime;
       if (rayConfig.runMode == RunMode.SINGLE_PROCESS) {
         runtime = new RayDevRuntime(rayConfig);
       } else {
-        runtime = new RayNativeRuntime(rayConfig);
+        if (rayConfig.workerMode == WorkerType.DRIVER) {
+          runtime = new RayNativeRuntime(rayConfig);
+        } else {
+          runtime = new RayMultiWorkerNativeRuntime(rayConfig);
+        }
       }
-
-      runtime.start();
       return runtime;
     } catch (Exception e) {
       LOGGER.error("Failed to initialize ray runtime", e);
diff --git a/java/runtime/src/main/java/org/ray/runtime/RayDevRuntime.java b/java/runtime/src/main/java/org/ray/runtime/RayDevRuntime.java
index 7653177a1..c96b811ce 100644
--- a/java/runtime/src/main/java/org/ray/runtime/RayDevRuntime.java
+++ b/java/runtime/src/main/java/org/ray/runtime/RayDevRuntime.java
@@ -11,14 +11,10 @@ import org.ray.runtime.task.TaskExecutor;
 
 public class RayDevRuntime extends AbstractRayRuntime {
 
-  public RayDevRuntime(RayConfig rayConfig) {
-    super(rayConfig);
-  }
-
   private AtomicInteger jobCounter = new AtomicInteger(0);
 
-  @Override
-  public void start() {
+  public RayDevRuntime(RayConfig rayConfig) {
+    super(rayConfig);
     if (rayConfig.getJobId().isNil()) {
       rayConfig.setJobId(nextJobId());
     }
diff --git a/java/runtime/src/main/java/org/ray/runtime/RayMultiWorkerNativeRuntime.java b/java/runtime/src/main/java/org/ray/runtime/RayMultiWorkerNativeRuntime.java
new file mode 100644
index 000000000..8c85048c9
--- /dev/null
+++ b/java/runtime/src/main/java/org/ray/runtime/RayMultiWorkerNativeRuntime.java
@@ -0,0 +1,192 @@
+package org.ray.runtime;
+
+import com.google.common.base.Preconditions;
+import java.util.List;
+import java.util.concurrent.Callable;
+import org.ray.api.RayActor;
+import org.ray.api.RayObject;
+import org.ray.api.RayPyActor;
+import org.ray.api.WaitResult;
+import org.ray.api.function.RayFunc;
+import org.ray.api.id.ObjectId;
+import org.ray.api.id.UniqueId;
+import org.ray.api.options.ActorCreationOptions;
+import org.ray.api.options.CallOptions;
+import org.ray.api.runtime.RayRuntime;
+import org.ray.api.runtimecontext.RuntimeContext;
+import org.ray.runtime.config.RayConfig;
+import org.ray.runtime.config.RunMode;
+import org.ray.runtime.generated.Common.WorkerType;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * This is a proxy runtime for multi-worker support. It holds multiple {@link RayNativeRuntime}
+ * instances and redirect calls to the correct one based on thread context.
+ */
+public class RayMultiWorkerNativeRuntime implements RayRuntime {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(RayMultiWorkerNativeRuntime.class);
+
+  /**
+   * The number of workers per worker process.
+   */
+  private final int numWorkers;
+  /**
+   * The worker threads.
+   */
+  private final Thread[] threads;
+  /**
+   * The {@link RayNativeRuntime} instances of workers.
+   */
+  private final RayNativeRuntime[] runtimes;
+  /**
+   * The {@link RayNativeRuntime} instance of current thread.
+   */
+  private final ThreadLocal<RayNativeRuntime> currentThreadRuntime = new ThreadLocal<>();
+
+  public RayMultiWorkerNativeRuntime(RayConfig rayConfig) {
+    Preconditions.checkState(
+        rayConfig.runMode == RunMode.CLUSTER && rayConfig.workerMode == WorkerType.WORKER);
+    Preconditions.checkState(rayConfig.numWorkersPerProcess > 0,
+        "numWorkersPerProcess must be greater than 0.");
+    numWorkers = rayConfig.numWorkersPerProcess;
+    runtimes = new RayNativeRuntime[numWorkers];
+    threads = new Thread[numWorkers];
+
+    LOGGER.info("Starting {} workers.", numWorkers);
+
+    for (int i = 0; i < numWorkers; i++) {
+      final int workerIndex = i;
+      threads[i] = new Thread(() -> {
+        RayNativeRuntime runtime = new RayNativeRuntime(rayConfig);
+        runtimes[workerIndex] = runtime;
+        currentThreadRuntime.set(runtime);
+        runtime.run();
+      });
+    }
+  }
+
+  public void run() {
+    for (int i = 0; i < numWorkers; i++) {
+      threads[i].start();
+    }
+    for (int i = 0; i < numWorkers; i++) {
+      try {
+        threads[i].join();
+      } catch (InterruptedException e) {
+        throw new RuntimeException(e);
+      }
+    }
+  }
+
+  @Override
+  public void shutdown() {
+    for (int i = 0; i < numWorkers; i++) {
+      runtimes[i].shutdown();
+    }
+    for (int i = 0; i < numWorkers; i++) {
+      try {
+        threads[i].join();
+      } catch (InterruptedException e) {
+        throw new RuntimeException(e);
+      }
+    }
+  }
+
+  public RayNativeRuntime getCurrentRuntime() {
+    RayNativeRuntime currentRuntime = currentThreadRuntime.get();
+    Preconditions.checkNotNull(currentRuntime,
+        "RayRuntime is not set on current thread."
+            + " If you want to use Ray API in your own threads,"
+            + " please wrap your `Runnable`s or `Callable`s with"
+            + " `Ray.wrapRunnable` or `Ray.wrapCallable`.");
+    return currentRuntime;
+  }
+
+  @Override
+  public <T> RayObject<T> put(T obj) {
+    return getCurrentRuntime().put(obj);
+  }
+
+  @Override
+  public <T> T get(ObjectId objectId) {
+    return getCurrentRuntime().get(objectId);
+  }
+
+  @Override
+  public <T> List<T> get(List<ObjectId> objectIds) {
+    return getCurrentRuntime().get(objectIds);
+  }
+
+  @Override
+  public <T> WaitResult<T> wait(List<RayObject<T>> waitList, int numReturns, int timeoutMs) {
+    return getCurrentRuntime().wait(waitList, numReturns, timeoutMs);
+  }
+
+  @Override
+  public void free(List<ObjectId> objectIds, boolean localOnly, boolean deleteCreatingTasks) {
+    getCurrentRuntime().free(objectIds, localOnly, deleteCreatingTasks);
+  }
+
+  @Override
+  public void setResource(String resourceName, double capacity, UniqueId nodeId) {
+    getCurrentRuntime().setResource(resourceName, capacity, nodeId);
+  }
+
+  @Override
+  public RayObject call(RayFunc func, Object[] args, CallOptions options) {
+    return getCurrentRuntime().call(func, args, options);
+  }
+
+  @Override
+  public RayObject call(RayFunc func, RayActor<?> actor, Object[] args) {
+    return getCurrentRuntime().call(func, actor, args);
+  }
+
+  @Override
+  public <T> RayActor<T> createActor(RayFunc actorFactoryFunc, Object[] args,
+      ActorCreationOptions options) {
+    return getCurrentRuntime().createActor(actorFactoryFunc, args, options);
+  }
+
+  @Override
+  public RuntimeContext getRuntimeContext() {
+    return getCurrentRuntime().getRuntimeContext();
+  }
+
+  @Override
+  public RayObject callPy(String moduleName, String functionName, Object[] args,
+      CallOptions options) {
+    return getCurrentRuntime().callPy(moduleName, functionName, args, options);
+  }
+
+  @Override
+  public RayObject callPy(RayPyActor pyActor, String functionName, Object[] args) {
+    return getCurrentRuntime().callPy(pyActor, functionName, args);
+  }
+
+  @Override
+  public RayPyActor createPyActor(String moduleName, String className, Object[] args,
+      ActorCreationOptions options) {
+    return getCurrentRuntime().createPyActor(moduleName, className, args, options);
+  }
+
+  @Override
+  public Runnable wrapRunnable(Runnable runnable) {
+    RayNativeRuntime runtime = getCurrentRuntime();
+    return () -> {
+      currentThreadRuntime.set(runtime);
+      runnable.run();
+    };
+  }
+
+  @Override
+  public Callable wrapCallable(Callable callable) {
+    RayNativeRuntime runtime = getCurrentRuntime();
+    return () -> {
+      currentThreadRuntime.set(runtime);
+      return callable.call();
+    };
+  }
+}
diff --git a/java/runtime/src/main/java/org/ray/runtime/RayNativeRuntime.java b/java/runtime/src/main/java/org/ray/runtime/RayNativeRuntime.java
index 28a0d0828..99908636d 100644
--- a/java/runtime/src/main/java/org/ray/runtime/RayNativeRuntime.java
+++ b/java/runtime/src/main/java/org/ray/runtime/RayNativeRuntime.java
@@ -2,9 +2,12 @@ package org.ray.runtime;
 
 import com.google.common.base.Preconditions;
 import com.google.common.base.Strings;
+import java.io.File;
+import java.io.IOException;
 import java.lang.reflect.Field;
 import java.util.HashMap;
 import java.util.Map;
+import org.apache.commons.io.FileUtils;
 import org.ray.api.id.JobId;
 import org.ray.runtime.config.RayConfig;
 import org.ray.runtime.context.NativeWorkerContext;
@@ -46,15 +49,20 @@ public final class RayNativeRuntime extends AbstractRayRuntime {
       }
       LOGGER.debug("Native libraries loaded.");
     }
-    nativeSetup(RayConfig.create().logDir);
+
+    RayConfig globalRayConfig = RayConfig.create();
+    resetLibraryPath(globalRayConfig);
+
+    try {
+      FileUtils.forceMkdir(new File(globalRayConfig.logDir));
+    } catch (IOException e) {
+      throw new RuntimeException("Failed to create the log directory.", e);
+    }
+    nativeSetup(globalRayConfig.logDir);
     Runtime.getRuntime().addShutdownHook(new Thread(RayNativeRuntime::nativeShutdownHook));
   }
 
-  public RayNativeRuntime(RayConfig rayConfig) {
-    super(rayConfig);
-  }
-
-  protected void resetLibraryPath() {
+  private static void resetLibraryPath(RayConfig rayConfig) {
     if (rayConfig.libraryPath.isEmpty()) {
       return;
     }
@@ -81,10 +89,11 @@ public final class RayNativeRuntime extends AbstractRayRuntime {
     }
   }
 
-  @Override
-  public void start() {
+  public RayNativeRuntime(RayConfig rayConfig) {
+    super(rayConfig);
+
     // Reset library path at runtime.
-    resetLibraryPath();
+    resetLibraryPath(rayConfig);
 
     if (rayConfig.getRedisAddress() == null) {
       manager = new RunManager(rayConfig);
diff --git a/java/runtime/src/main/java/org/ray/runtime/config/RayConfig.java b/java/runtime/src/main/java/org/ray/runtime/config/RayConfig.java
index 05e18ed27..3be4bee26 100644
--- a/java/runtime/src/main/java/org/ray/runtime/config/RayConfig.java
+++ b/java/runtime/src/main/java/org/ray/runtime/config/RayConfig.java
@@ -62,6 +62,8 @@ public class RayConfig {
    */
   public final int numberExecThreadsForDevRuntime;
 
+  public final int numWorkersPerProcess;
+
   private void validate() {
     if (workerMode == WorkerType.WORKER) {
       Preconditions.checkArgument(redisAddress != null,
@@ -171,6 +173,8 @@ public class RayConfig {
     // Number of threads that execute tasks.
     numberExecThreadsForDevRuntime = config.getInt("ray.dev-runtime.execution-parallelism");
 
+    numWorkersPerProcess = config.getInt("ray.raylet.config.num_workers_per_process_java");
+
     // Validate config.
     validate();
     LOGGER.debug("Created config: {}", this);
diff --git a/java/runtime/src/main/java/org/ray/runtime/runner/RunManager.java b/java/runtime/src/main/java/org/ray/runtime/runner/RunManager.java
index 97f6dd135..7434e3890 100644
--- a/java/runtime/src/main/java/org/ray/runtime/runner/RunManager.java
+++ b/java/runtime/src/main/java/org/ray/runtime/runner/RunManager.java
@@ -320,10 +320,13 @@ public class RunManager {
       cmd.add("-Dray.redis.password=" + rayConfig.headRedisPassword);
     }
 
+    // Number of workers per Java worker process
+    cmd.add("-Dray.raylet.config.num_workers_per_process_java=RAY_WORKER_NUM_WORKERS_PLACEHOLDER");
+
     cmd.addAll(rayConfig.jvmParameters);
 
     // jvm options
-    cmd.add("RAY_WORKER_OPTION_0");
+    cmd.add("RAY_WORKER_DYNAMIC_OPTION_PLACEHOLDER_0");
 
     // Main class
     cmd.add(WORKER_CLASS);
diff --git a/java/runtime/src/main/java/org/ray/runtime/runner/worker/DefaultWorker.java b/java/runtime/src/main/java/org/ray/runtime/runner/worker/DefaultWorker.java
index 698c14973..fad4ec2aa 100644
--- a/java/runtime/src/main/java/org/ray/runtime/runner/worker/DefaultWorker.java
+++ b/java/runtime/src/main/java/org/ray/runtime/runner/worker/DefaultWorker.java
@@ -1,6 +1,8 @@
 package org.ray.runtime.runner.worker;
 
 import org.ray.api.Ray;
+import org.ray.api.runtime.RayRuntime;
+import org.ray.runtime.RayMultiWorkerNativeRuntime;
 import org.ray.runtime.RayNativeRuntime;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -20,7 +22,14 @@ public class DefaultWorker {
       });
       Ray.init();
       LOGGER.info("Worker started.");
-      ((RayNativeRuntime)Ray.internal()).run();
+      RayRuntime runtime = Ray.internal();
+      if (runtime instanceof RayNativeRuntime) {
+        ((RayNativeRuntime)runtime).run();
+      } else if (runtime instanceof RayMultiWorkerNativeRuntime) {
+        ((RayMultiWorkerNativeRuntime)runtime).run();
+      } else {
+        throw new RuntimeException("Unknown RayRuntime: " + runtime);
+      }
     } catch (Exception e) {
       LOGGER.error("Failed to start worker.", e);
     }
diff --git a/java/runtime/src/main/java/org/ray/runtime/task/ArgumentsBuilder.java b/java/runtime/src/main/java/org/ray/runtime/task/ArgumentsBuilder.java
index 110c178f7..c74932c8f 100644
--- a/java/runtime/src/main/java/org/ray/runtime/task/ArgumentsBuilder.java
+++ b/java/runtime/src/main/java/org/ray/runtime/task/ArgumentsBuilder.java
@@ -5,7 +5,9 @@ import java.util.List;
 import org.ray.api.Ray;
 import org.ray.api.RayObject;
 import org.ray.api.id.ObjectId;
+import org.ray.api.runtime.RayRuntime;
 import org.ray.runtime.AbstractRayRuntime;
+import org.ray.runtime.RayMultiWorkerNativeRuntime;
 import org.ray.runtime.object.NativeRayObject;
 import org.ray.runtime.object.ObjectStore;
 import org.ray.runtime.util.Serializer;
@@ -41,7 +43,11 @@ public class ArgumentsBuilder {
       } else {
         byte[] serialized = Serializer.encode(arg);
         if (serialized.length > LARGEST_SIZE_PASS_BY_VALUE) {
-          id = ((AbstractRayRuntime) Ray.internal()).getObjectStore()
+          RayRuntime runtime = Ray.internal();
+          if (runtime instanceof RayMultiWorkerNativeRuntime) {
+            runtime = ((RayMultiWorkerNativeRuntime) runtime).getCurrentRuntime();
+          }
+          id = ((AbstractRayRuntime) runtime).getObjectStore()
               .put(new NativeRayObject(serialized, null));
         } else {
           data = serialized;
diff --git a/java/runtime/src/main/resources/ray.default.conf b/java/runtime/src/main/resources/ray.default.conf
index c5fd12e92..3da6089d7 100644
--- a/java/runtime/src/main/resources/ray.default.conf
+++ b/java/runtime/src/main/resources/ray.default.conf
@@ -87,6 +87,7 @@ ray {
 
     // See src/ray/ray_config_def.h for options.
     config {
+      num_workers_per_process_java: 10
     }
   }
 
diff --git a/java/test/src/main/java/org/ray/api/TestUtils.java b/java/test/src/main/java/org/ray/api/TestUtils.java
index 3badb1104..a03bd627f 100644
--- a/java/test/src/main/java/org/ray/api/TestUtils.java
+++ b/java/test/src/main/java/org/ray/api/TestUtils.java
@@ -1,8 +1,11 @@
 package org.ray.api;
 
+import com.google.common.base.Preconditions;
 import java.util.function.Supplier;
 import org.ray.api.annotation.RayRemote;
+import org.ray.api.runtime.RayRuntime;
 import org.ray.runtime.AbstractRayRuntime;
+import org.ray.runtime.RayMultiWorkerNativeRuntime;
 import org.ray.runtime.config.RunMode;
 import org.testng.Assert;
 import org.testng.SkipException;
@@ -12,8 +15,7 @@ public class TestUtils {
   private static final int WAIT_INTERVAL_MS = 5;
 
   public static void skipTestUnderSingleProcess() {
-    AbstractRayRuntime runtime = (AbstractRayRuntime)Ray.internal();
-    if (runtime.getRayConfig().runMode == RunMode.SINGLE_PROCESS) {
+    if (getRuntime().getRayConfig().runMode == RunMode.SINGLE_PROCESS) {
       throw new SkipException("This test doesn't work under single-process mode.");
     }
   }
@@ -62,4 +64,13 @@ public class TestUtils {
     RayObject<String> obj = Ray.call(TestUtils::hi);
     Assert.assertEquals(obj.get(), "hi");
   }
+
+  public static AbstractRayRuntime getRuntime() {
+    RayRuntime runtime = Ray.internal();
+    if (runtime instanceof RayMultiWorkerNativeRuntime) {
+      runtime = ((RayMultiWorkerNativeRuntime) runtime).getCurrentRuntime();
+    }
+    Preconditions.checkState(runtime instanceof AbstractRayRuntime);
+    return (AbstractRayRuntime) runtime;
+  }
 }
diff --git a/java/test/src/main/java/org/ray/api/test/ActorTest.java b/java/test/src/main/java/org/ray/api/test/ActorTest.java
index 0f4e08fa6..a8870558e 100644
--- a/java/test/src/main/java/org/ray/api/test/ActorTest.java
+++ b/java/test/src/main/java/org/ray/api/test/ActorTest.java
@@ -11,7 +11,6 @@ import org.ray.api.TestUtils;
 import org.ray.api.annotation.RayRemote;
 import org.ray.api.exception.UnreconstructableException;
 import org.ray.api.id.UniqueId;
-import org.ray.runtime.AbstractRayRuntime;
 import org.ray.runtime.actor.NativeRayActor;
 import org.ray.runtime.object.NativeRayObject;
 import org.testng.Assert;
@@ -117,7 +116,7 @@ public class ActorTest extends BaseTest {
     Ray.internal().free(ImmutableList.of(value.getId()), false, false);
     // Wait until the object is deleted, because the above free operation is async.
     while (true) {
-      NativeRayObject result = ((AbstractRayRuntime) Ray.internal()).getObjectStore()
+      NativeRayObject result = TestUtils.getRuntime().getObjectStore()
           .getRaw(ImmutableList.of(value.getId()), 0).get(0);
       if (result == null) {
         break;
diff --git a/java/test/src/main/java/org/ray/api/test/BaseMultiLanguageTest.java b/java/test/src/main/java/org/ray/api/test/BaseMultiLanguageTest.java
index 939372b96..0603a917e 100644
--- a/java/test/src/main/java/org/ray/api/test/BaseMultiLanguageTest.java
+++ b/java/test/src/main/java/org/ray/api/test/BaseMultiLanguageTest.java
@@ -1,5 +1,6 @@
 package org.ray.api.test;
 
+import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import java.io.File;
@@ -63,7 +64,7 @@ public abstract class BaseMultiLanguageTest {
     // Start ray cluster.
     String workerOptions =
         " -classpath " + System.getProperty("java.class.path");
-    final List<String> startCommand = ImmutableList.of(
+    List<String> startCommand = ImmutableList.of(
         "ray",
         "start",
         "--head",
@@ -74,6 +75,13 @@ public abstract class BaseMultiLanguageTest {
         "--include-java",
         "--java-worker-options=" + workerOptions
     );
+    String numWorkersPerProcessJava = System
+        .getProperty("ray.raylet.config.num_workers_per_process_java");
+    if (!Strings.isNullOrEmpty(numWorkersPerProcessJava)) {
+      startCommand = ImmutableList.<String>builder().addAll(startCommand)
+          .add(String.format("--internal-config={\"num_workers_per_process_java\": %s}",
+              numWorkersPerProcessJava)).build();
+    }
     if (!executeCommand(startCommand, 10, getRayStartEnv())) {
       throw new RuntimeException("Couldn't start ray cluster.");
     }
diff --git a/java/test/src/main/java/org/ray/api/test/FailureTest.java b/java/test/src/main/java/org/ray/api/test/FailureTest.java
index b47b010ae..4dbcbcf4b 100644
--- a/java/test/src/main/java/org/ray/api/test/FailureTest.java
+++ b/java/test/src/main/java/org/ray/api/test/FailureTest.java
@@ -127,6 +127,7 @@ public class FailureTest extends BaseTest {
     TestUtils.skipTestUnderSingleProcess();
     List<RayFunc0<Integer>> badFunctions = Arrays.asList(FailureTest::badFunc,
         FailureTest::badFunc2);
+    TestUtils.warmUpCluster();
     for (RayFunc0<Integer> badFunc : badFunctions) {
       RayObject<Integer> obj1 = Ray.call(badFunc);
       RayObject<Integer> obj2 = Ray.call(FailureTest::slowFunc);
diff --git a/java/test/src/main/java/org/ray/api/test/GcsClientTest.java b/java/test/src/main/java/org/ray/api/test/GcsClientTest.java
index 04b08b64b..bd778f91b 100644
--- a/java/test/src/main/java/org/ray/api/test/GcsClientTest.java
+++ b/java/test/src/main/java/org/ray/api/test/GcsClientTest.java
@@ -2,11 +2,9 @@ package org.ray.api.test;
 
 import com.google.common.base.Preconditions;
 import java.util.List;
-import org.ray.api.Ray;
 import org.ray.api.TestUtils;
 import org.ray.api.id.JobId;
 import org.ray.api.runtimecontext.NodeInfo;
-import org.ray.runtime.AbstractRayRuntime;
 import org.ray.runtime.config.RayConfig;
 import org.ray.runtime.gcs.GcsClient;
 import org.testng.Assert;
@@ -29,10 +27,10 @@ public class GcsClientTest extends BaseTest {
   @Test
   public void testGetAllNodeInfo() {
     TestUtils.skipTestUnderSingleProcess();
-    RayConfig config = ((AbstractRayRuntime)Ray.internal()).getRayConfig();
+    RayConfig config = TestUtils.getRuntime().getRayConfig();
 
     Preconditions.checkNotNull(config);
-    GcsClient gcsClient = ((AbstractRayRuntime)Ray.internal()).getGcsClient();
+    GcsClient gcsClient = TestUtils.getRuntime().getGcsClient();
     List<NodeInfo> allNodeInfo = gcsClient.getAllNodeInfo();
     Assert.assertEquals(allNodeInfo.size(), 1);
     Assert.assertEquals(allNodeInfo.get(0).nodeAddress, config.nodeIp);
@@ -43,11 +41,11 @@ public class GcsClientTest extends BaseTest {
   @Test
   public void testNextJob() {
     TestUtils.skipTestUnderSingleProcess();
-    RayConfig config = ((AbstractRayRuntime)Ray.internal()).getRayConfig();
+    RayConfig config = TestUtils.getRuntime().getRayConfig();
     // The value of job id of this driver in cluster should be `1L`.
     Assert.assertEquals(config.getJobId(), JobId.fromInt(1));
 
-    GcsClient gcsClient = ((AbstractRayRuntime)Ray.internal()).getGcsClient();
+    GcsClient gcsClient = TestUtils.getRuntime().getGcsClient();
     for (int i  = 2; i < 100; ++i) {
       Assert.assertEquals(gcsClient.nextJobId(), JobId.fromInt(i));
     }
diff --git a/java/test/src/main/java/org/ray/api/test/MultiThreadingTest.java b/java/test/src/main/java/org/ray/api/test/MultiThreadingTest.java
index 86fdc1b94..ce2fb2452 100644
--- a/java/test/src/main/java/org/ray/api/test/MultiThreadingTest.java
+++ b/java/test/src/main/java/org/ray/api/test/MultiThreadingTest.java
@@ -54,19 +54,22 @@ public class MultiThreadingTest extends BaseTest {
     }
 
     @RayRemote
-    public ActorId getCurrentActorId() {
-      final ActorId[] result = new ActorId[1];
-      Thread thread = new Thread(() -> {
-        result[0] = Ray.getRuntimeContext().getCurrentActorId();
-      });
+    public ActorId getCurrentActorId() throws Exception {
+      final Object[] result = new Object[1];
+      Thread thread = new Thread(Ray.wrapRunnable(() -> {
+        try {
+          result[0] = Ray.getRuntimeContext().getCurrentActorId();
+        } catch (Exception e) {
+          result[0] = e;
+        }
+      }));
       thread.start();
-      try {
-        thread.join();
-      } catch (InterruptedException e) {
-        throw new RuntimeException(e);
+      thread.join();
+      if (result[0] instanceof Exception) {
+        throw (Exception) result[0];
       }
       Assert.assertEquals(result[0], actorId);
-      return result[0];
+      return (ActorId) result[0];
     }
   }
 
@@ -147,13 +150,13 @@ public class MultiThreadingTest extends BaseTest {
     try {
       List<Future<String>> futures = new ArrayList<>();
       for (int i = 0; i < NUM_THREADS; i++) {
-        Callable<String> task = () -> {
+        Callable<String> task = Ray.wrapCallable(() -> {
           for (int j = 0; j < numRepeats; j++) {
             TimeUnit.MILLISECONDS.sleep(1);
             testCase.run();
           }
           return "ok";
-        };
+        });
         futures.add(service.submit(task));
       }
       for (Future<String> future : futures) {
diff --git a/java/test/src/main/java/org/ray/api/test/PlasmaFreeTest.java b/java/test/src/main/java/org/ray/api/test/PlasmaFreeTest.java
index e0d18d9a5..395209ad5 100644
--- a/java/test/src/main/java/org/ray/api/test/PlasmaFreeTest.java
+++ b/java/test/src/main/java/org/ray/api/test/PlasmaFreeTest.java
@@ -7,7 +7,6 @@ import org.ray.api.RayObject;
 import org.ray.api.TestUtils;
 import org.ray.api.annotation.RayRemote;
 import org.ray.api.id.TaskId;
-import org.ray.runtime.AbstractRayRuntime;
 import org.testng.Assert;
 import org.testng.annotations.Test;
 
@@ -26,7 +25,7 @@ public class PlasmaFreeTest extends BaseTest {
     Ray.internal().free(ImmutableList.of(helloId.getId()), true, false);
 
     final boolean result = TestUtils.waitForCondition(() ->
-        ((AbstractRayRuntime) Ray.internal()).getObjectStore()
+        TestUtils.getRuntime().getObjectStore()
             .getRaw(ImmutableList.of(helloId.getId()), 0).get(0) == null, 50);
     Assert.assertTrue(result);
   }
@@ -40,7 +39,7 @@ public class PlasmaFreeTest extends BaseTest {
 
     TaskId taskId = TaskId.fromBytes(Arrays.copyOf(helloId.getId().getBytes(), TaskId.LENGTH));
     final boolean result = TestUtils.waitForCondition(
-        () -> !(((AbstractRayRuntime) Ray.internal()).getGcsClient())
+        () -> !TestUtils.getRuntime().getGcsClient()
             .rayletTaskExistsInGcs(taskId), 50);
     Assert.assertTrue(result);
   }
diff --git a/java/test/src/main/java/org/ray/api/test/PlasmaStoreTest.java b/java/test/src/main/java/org/ray/api/test/PlasmaStoreTest.java
index fc0a06e91..e0655e052 100644
--- a/java/test/src/main/java/org/ray/api/test/PlasmaStoreTest.java
+++ b/java/test/src/main/java/org/ray/api/test/PlasmaStoreTest.java
@@ -1,11 +1,8 @@
 package org.ray.api.test;
 
-import java.util.Collections;
 import org.ray.api.Ray;
 import org.ray.api.TestUtils;
 import org.ray.api.id.ObjectId;
-import org.ray.runtime.AbstractRayRuntime;
-import org.ray.runtime.object.NativeRayObject;
 import org.ray.runtime.object.ObjectStore;
 import org.testng.Assert;
 import org.testng.annotations.Test;
@@ -16,8 +13,7 @@ public class PlasmaStoreTest extends BaseTest {
   public void testPutWithDuplicateId() {
     TestUtils.skipTestUnderSingleProcess();
     ObjectId objectId = ObjectId.fromRandom();
-    AbstractRayRuntime runtime = (AbstractRayRuntime) Ray.internal();
-    ObjectStore objectStore = runtime.getObjectStore();
+    ObjectStore objectStore = TestUtils.getRuntime().getObjectStore();
     objectStore.put("1", objectId);
     Assert.assertEquals(Ray.get(objectId), "1");
     objectStore.put("2", objectId);
diff --git a/java/test/src/main/java/org/ray/api/test/RayCallTest.java b/java/test/src/main/java/org/ray/api/test/RayCallTest.java
index 37def8733..db496e2b8 100644
--- a/java/test/src/main/java/org/ray/api/test/RayCallTest.java
+++ b/java/test/src/main/java/org/ray/api/test/RayCallTest.java
@@ -6,9 +6,9 @@ import java.io.Serializable;
 import java.util.List;
 import java.util.Map;
 import org.ray.api.Ray;
+import org.ray.api.TestUtils;
 import org.ray.api.annotation.RayRemote;
 import org.ray.api.id.ObjectId;
-import org.ray.runtime.AbstractRayRuntime;
 import org.testng.Assert;
 import org.testng.annotations.Test;
 
@@ -80,7 +80,7 @@ public class RayCallTest extends BaseTest {
   @RayRemote
   private static void testNoReturn(ObjectId objectId) {
     // Put an object in object store to inform driver that this function is executing.
-    ((AbstractRayRuntime) Ray.internal()).getObjectStore().put(1, objectId);
+    TestUtils.getRuntime().getObjectStore().put(1, objectId);
   }
 
   /**
diff --git a/java/test/src/main/java/org/ray/api/test/RaySerializerTest.java b/java/test/src/main/java/org/ray/api/test/RaySerializerTest.java
index 729815c23..0cb8c6b23 100644
--- a/java/test/src/main/java/org/ray/api/test/RaySerializerTest.java
+++ b/java/test/src/main/java/org/ray/api/test/RaySerializerTest.java
@@ -2,8 +2,8 @@ package org.ray.api.test;
 
 import org.ray.api.Ray;
 import org.ray.api.RayPyActor;
+import org.ray.api.TestUtils;
 import org.ray.api.id.ObjectId;
-import org.ray.runtime.AbstractRayRuntime;
 import org.ray.runtime.object.NativeRayObject;
 import org.ray.runtime.object.ObjectStore;
 import org.testng.Assert;
@@ -14,7 +14,7 @@ public class RaySerializerTest extends BaseMultiLanguageTest {
   @Test
   public void testSerializePyActor() {
     RayPyActor pyActor = Ray.createPyActor("test", "RaySerializerTest");
-    ObjectStore objectStore = ((AbstractRayRuntime) Ray.internal()).getObjectStore();
+    ObjectStore objectStore = TestUtils.getRuntime().getObjectStore();
     NativeRayObject nativeRayObject = objectStore.serialize(pyActor);
     RayPyActor result = (RayPyActor) objectStore
         .deserialize(nativeRayObject, ObjectId.fromRandom());
diff --git a/python/ray/includes/ray_config.pxd b/python/ray/includes/ray_config.pxd
index 41adec160..4d3a76ec7 100644
--- a/python/ray/includes/ray_config.pxd
+++ b/python/ray/includes/ray_config.pxd
@@ -76,7 +76,9 @@ cdef extern from "ray/common/ray_config.h" nogil:
 
         uint64_t object_manager_default_chunk_size() const
 
-        int num_workers_per_process() const
+        int num_workers_per_process_python() const
+
+        int num_workers_per_process_java() const
 
         int64_t max_task_lease_timeout_ms() const
 
diff --git a/python/ray/includes/ray_config.pxi b/python/ray/includes/ray_config.pxi
index 03f9a8df5..7171884ee 100644
--- a/python/ray/includes/ray_config.pxi
+++ b/python/ray/includes/ray_config.pxi
@@ -142,8 +142,12 @@ cdef class Config:
         return RayConfig.instance().object_manager_default_chunk_size()
 
     @staticmethod
-    def num_workers_per_process():
-        return RayConfig.instance().num_workers_per_process()
+    def num_workers_per_process_python():
+        return RayConfig.instance().num_workers_per_process_python()
+
+    @staticmethod
+    def num_workers_per_process_java():
+        return RayConfig.instance().num_workers_per_process_java()
 
     @staticmethod
     def max_task_lease_timeout_ms():
diff --git a/python/ray/services.py b/python/ray/services.py
index b15fcbb84..5b806f8dc 100644
--- a/python/ray/services.py
+++ b/python/ray/services.py
@@ -1181,12 +1181,15 @@ def build_java_worker_command(
     command += "-Dray.home={} ".format(RAY_HOME)
     command += "-Dray.log-dir={} ".format(os.path.join(session_dir, "logs"))
 
+    command += ("-Dray.raylet.config.num_workers_per_process_java=" +
+                "RAY_WORKER_NUM_WORKERS_PLACEHOLDER ")
+
     if java_worker_options:
         # Put `java_worker_options` in the last, so it can overwrite the
         # above options.
         command += java_worker_options + " "
 
-    command += "RAY_WORKER_OPTION_0 "
+    command += "RAY_WORKER_DYNAMIC_OPTION_PLACEHOLDER_0 "
     command += "org.ray.runtime.runner.worker.DefaultWorker"
 
     return command
diff --git a/src/ray/common/constants.h b/src/ray/common/constants.h
index 5a82fed2d..e117d4bac 100644
--- a/src/ray/common/constants.h
+++ b/src/ray/common/constants.h
@@ -21,6 +21,9 @@ constexpr char kObjectTablePrefix[] = "ObjectTable";
 /// Prefix for the task table keys in redis.
 constexpr char kTaskTablePrefix[] = "TaskTable";
 
-constexpr char kWorkerDynamicOptionPlaceholderPrefix[] = "RAY_WORKER_OPTION_";
+constexpr char kWorkerDynamicOptionPlaceholderPrefix[] =
+    "RAY_WORKER_DYNAMIC_OPTION_PLACEHOLDER_";
+
+constexpr char kWorkerNumWorkersPlaceholder[] = "RAY_WORKER_NUM_WORKERS_PLACEHOLDER";
 
 #endif  // RAY_CONSTANTS_H_
diff --git a/src/ray/common/ray_config_def.h b/src/ray/common/ray_config_def.h
index d0a6000c6..e0720006a 100644
--- a/src/ray/common/ray_config_def.h
+++ b/src/ray/common/ray_config_def.h
@@ -137,8 +137,11 @@ RAY_CONFIG(int, object_manager_repeated_push_delay_ms, 60000)
 /// chunks exceeds the number of available sending threads.
 RAY_CONFIG(uint64_t, object_manager_default_chunk_size, 1000000)
 
-/// Number of workers per process
-RAY_CONFIG(int, num_workers_per_process, 1)
+/// Number of workers per Python worker process
+RAY_CONFIG(int, num_workers_per_process_python, 1)
+
+/// Number of workers per Java worker process
+RAY_CONFIG(int, num_workers_per_process_java, 10)
 
 /// Maximum timeout in milliseconds within which a task lease must be renewed.
 RAY_CONFIG(int64_t, max_task_lease_timeout_ms, 60000)
diff --git a/src/ray/core_worker/lib/java/org_ray_runtime_task_NativeTaskSubmitter.cc b/src/ray/core_worker/lib/java/org_ray_runtime_task_NativeTaskSubmitter.cc
index ca219ddae..beaa000b2 100644
--- a/src/ray/core_worker/lib/java/org_ray_runtime_task_NativeTaskSubmitter.cc
+++ b/src/ray/core_worker/lib/java/org_ray_runtime_task_NativeTaskSubmitter.cc
@@ -84,10 +84,12 @@ inline ray::ActorCreationOptions ToActorCreationOptions(JNIEnv *env,
     jobject java_resources =
         env->GetObjectField(actorCreationOptions, java_base_task_options_resources);
     resources = ToResources(env, java_resources);
-    std::string jvm_options = JavaStringToNativeString(
-        env, (jstring)env->GetObjectField(actorCreationOptions,
-                                          java_actor_creation_options_jvm_options));
-    dynamic_worker_options.emplace_back(jvm_options);
+    jstring java_jvm_options = (jstring)env->GetObjectField(
+        actorCreationOptions, java_actor_creation_options_jvm_options);
+    if (java_jvm_options) {
+      std::string jvm_options = JavaStringToNativeString(env, java_jvm_options);
+      dynamic_worker_options.emplace_back(jvm_options);
+    }
   }
 
   ray::ActorCreationOptions action_creation_options{
diff --git a/src/ray/protobuf/common.proto b/src/ray/protobuf/common.proto
index badcbea5b..15f17c2f5 100644
--- a/src/ray/protobuf/common.proto
+++ b/src/ray/protobuf/common.proto
@@ -85,8 +85,8 @@ message ActorCreationTaskSpec {
   uint64 max_actor_reconstructions = 3;
   // The dynamic options used in the worker command when starting a worker process for
   // an actor creation task. If the list isn't empty, the options will be used to replace
-  // the placeholder strings (`RAY_WORKER_OPTION_0`, `RAY_WORKER_OPTION_1`, etc) in the
-  // worker command.
+  // the placeholder strings (`RAY_WORKER_DYNAMIC_OPTION_PLACEHOLDER_0`,
+  // `RAY_WORKER_DYNAMIC_OPTION_PLACEHOLDER_1`, etc) in the worker command.
   repeated string dynamic_worker_options = 4;
 }
 
diff --git a/src/ray/raylet/main.cc b/src/ray/raylet/main.cc
index af68db41d..9a67ecfa8 100644
--- a/src/ray/raylet/main.cc
+++ b/src/ray/raylet/main.cc
@@ -104,8 +104,6 @@ int main(int argc, char *argv[]) {
   node_manager_config.node_manager_address = node_ip_address;
   node_manager_config.node_manager_port = node_manager_port;
   node_manager_config.num_initial_workers = num_initial_workers;
-  node_manager_config.num_workers_per_process =
-      RayConfig::instance().num_workers_per_process();
   node_manager_config.maximum_startup_concurrency = maximum_startup_concurrency;
 
   if (!python_worker_command.empty()) {
diff --git a/src/ray/raylet/node_manager.cc b/src/ray/raylet/node_manager.cc
index d74be41c6..fa113cce8 100644
--- a/src/ray/raylet/node_manager.cc
+++ b/src/ray/raylet/node_manager.cc
@@ -82,9 +82,8 @@ NodeManager::NodeManager(boost::asio::io_service &io_service,
       object_manager_profile_timer_(io_service),
       initial_config_(config),
       local_available_resources_(config.resource_config),
-      worker_pool_(config.num_initial_workers, config.num_workers_per_process,
-                   config.maximum_startup_concurrency, gcs_client_,
-                   config.worker_commands),
+      worker_pool_(config.num_initial_workers, config.maximum_startup_concurrency,
+                   gcs_client_, config.worker_commands),
       scheduling_policy_(local_queues_),
       reconstruction_policy_(
           io_service_,
diff --git a/src/ray/raylet/node_manager.h b/src/ray/raylet/node_manager.h
index 931853134..2afd90460 100644
--- a/src/ray/raylet/node_manager.h
+++ b/src/ray/raylet/node_manager.h
@@ -43,8 +43,6 @@ struct NodeManagerConfig {
   int node_manager_port;
   /// The initial number of workers to create.
   int num_initial_workers;
-  /// The number of workers per process.
-  int num_workers_per_process;
   /// The maximum number of workers that can be started concurrently by a
   /// worker pool.
   int maximum_startup_concurrency;
diff --git a/src/ray/raylet/object_manager_integration_test.cc b/src/ray/raylet/object_manager_integration_test.cc
index 73525f2e4..128a07e90 100644
--- a/src/ray/raylet/object_manager_integration_test.cc
+++ b/src/ray/raylet/object_manager_integration_test.cc
@@ -39,7 +39,6 @@ class TestObjectManagerBase : public ::testing::Test {
     node_manager_config.resource_config =
         ray::raylet::ResourceSet(std::move(static_resource_conf));
     node_manager_config.num_initial_workers = 0;
-    node_manager_config.num_workers_per_process = 1;
     // Use a default worker that can execute empty tasks with dependencies.
     std::vector<std::string> py_worker_command;
     py_worker_command.push_back("python");
diff --git a/src/ray/raylet/worker_pool.cc b/src/ray/raylet/worker_pool.cc
index f2e77c6cf..ade829870 100644
--- a/src/ray/raylet/worker_pool.cc
+++ b/src/ray/raylet/worker_pool.cc
@@ -40,17 +40,13 @@ namespace ray {
 namespace raylet {
 
 /// A constructor that initializes a worker pool with
-/// (num_worker_processes * num_workers_per_process) workers for each language.
-WorkerPool::WorkerPool(int num_worker_processes, int num_workers_per_process,
-                       int maximum_startup_concurrency,
+/// (num_worker_processes * states_by_lang_[language].num_workers_per_process) workers for
+/// each language.
+WorkerPool::WorkerPool(int num_worker_processes, int maximum_startup_concurrency,
                        std::shared_ptr<gcs::RedisGcsClient> gcs_client,
                        const WorkerCommandMap &worker_commands)
-    : num_workers_per_process_(num_workers_per_process),
-      multiple_for_warning_(std::max(num_worker_processes, maximum_startup_concurrency)),
-      maximum_startup_concurrency_(maximum_startup_concurrency),
-      last_warning_multiple_(0),
+    : maximum_startup_concurrency_(maximum_startup_concurrency),
       gcs_client_(std::move(gcs_client)) {
-  RAY_CHECK(num_workers_per_process > 0) << "num_workers_per_process must be positive.";
   RAY_CHECK(maximum_startup_concurrency > 0);
   // Ignore SIGCHLD signals. If we don't do this, then worker processes will
   // become zombies instead of dying gracefully.
@@ -58,6 +54,25 @@ WorkerPool::WorkerPool(int num_worker_processes, int num_workers_per_process,
   for (const auto &entry : worker_commands) {
     // Initialize the pool state for this language.
     auto &state = states_by_lang_[entry.first];
+    switch (entry.first) {
+    case Language::PYTHON:
+      state.num_workers_per_process =
+          RayConfig::instance().num_workers_per_process_python();
+      break;
+    case Language::JAVA:
+      state.num_workers_per_process =
+          RayConfig::instance().num_workers_per_process_java();
+      break;
+    default:
+      RAY_LOG(FATAL) << "The number of workers per process for "
+                     << Language_Name(entry.first) << " worker is not set.";
+    }
+    RAY_CHECK(state.num_workers_per_process > 0)
+        << "Number of workers per process of language " << Language_Name(entry.first)
+        << " must be positive.";
+    state.multiple_for_warning =
+        std::max(num_worker_processes, maximum_startup_concurrency) *
+        state.num_workers_per_process;
     // Set worker command for this language.
     state.worker_command = entry.second;
     RAY_CHECK(!state.worker_command.empty()) << "Worker command must not be empty.";
@@ -119,9 +134,17 @@ int WorkerPool::StartWorkerProcess(const Language &language,
                  << state.idle_actor.size() << " actor workers, and " << state.idle.size()
                  << " non-actor workers";
 
+  int workers_to_start;
+  if (dynamic_options.empty()) {
+    workers_to_start = state.num_workers_per_process;
+  } else {
+    workers_to_start = 1;
+  }
+
   // Extract pointers from the worker command to pass into execvp.
   std::vector<std::string> worker_command_args;
   size_t dynamic_option_index = 0;
+  bool num_workers_arg_replaced = false;
   for (auto const &token : state.worker_command) {
     const auto option_placeholder =
         kWorkerDynamicOptionPlaceholderPrefix + std::to_string(dynamic_option_index);
@@ -135,9 +158,22 @@ int WorkerPool::StartWorkerProcess(const Language &language,
         ++dynamic_option_index;
       }
     } else {
-      worker_command_args.push_back(token);
+      size_t num_workers_index = token.find(kWorkerNumWorkersPlaceholder);
+      if (num_workers_index != std::string::npos) {
+        std::string arg = token;
+        worker_command_args.push_back(arg.replace(num_workers_index,
+                                                  strlen(kWorkerNumWorkersPlaceholder),
+                                                  std::to_string(workers_to_start)));
+        num_workers_arg_replaced = true;
+      } else {
+        worker_command_args.push_back(token);
+      }
     }
   }
+  RAY_CHECK(num_workers_arg_replaced || state.num_workers_per_process == 1)
+      << "Expect to start " << state.num_workers_per_process << " workers per "
+      << Language_Name(language) << " worker process. But the "
+      << kWorkerNumWorkersPlaceholder << "placeholder is not found in worker command.";
 
   pid_t pid = StartProcess(worker_command_args);
   if (pid < 0) {
@@ -145,9 +181,9 @@ int WorkerPool::StartWorkerProcess(const Language &language,
     RAY_LOG(FATAL) << "Failed to fork worker process: " << strerror(errno);
   } else if (pid > 0) {
     // Parent process case.
-    RAY_LOG(DEBUG) << "Started worker process with pid " << pid;
-    state.starting_worker_processes.emplace(
-        std::make_pair(pid, num_workers_per_process_));
+    RAY_LOG(DEBUG) << "Started worker process of " << workers_to_start
+                   << " worker(s) with pid " << pid;
+    state.starting_worker_processes.emplace(pid, workers_to_start);
     return pid;
   }
   return -1;
@@ -355,27 +391,30 @@ std::vector<std::shared_ptr<Worker>> WorkerPool::GetWorkersRunningTasksForJob(
 }
 
 void WorkerPool::WarnAboutSize() {
-  int64_t num_workers_started_or_registered = 0;
   for (const auto &entry : states_by_lang_) {
+    auto state = entry.second;
+    int64_t num_workers_started_or_registered = 0;
     num_workers_started_or_registered +=
-        static_cast<int64_t>(entry.second.registered_workers.size());
-    num_workers_started_or_registered +=
-        static_cast<int64_t>(entry.second.starting_worker_processes.size());
-  }
-  int64_t multiple = num_workers_started_or_registered / multiple_for_warning_;
-  std::stringstream warning_message;
-  if (multiple >= 3 && multiple > last_warning_multiple_) {
-    // Push an error message to the user if the worker pool tells us that it is
-    // getting too big.
-    last_warning_multiple_ = multiple;
-    warning_message << "WARNING: " << num_workers_started_or_registered
-                    << " workers have been started. This could be a result of using "
-                    << "a large number of actors, or it could be a consequence of "
-                    << "using nested tasks "
-                    << "(see https://github.com/ray-project/ray/issues/3644) for "
-                    << "some a discussion of workarounds.";
-    RAY_CHECK_OK(gcs_client_->error_table().PushErrorToDriver(
-        JobID::Nil(), "worker_pool_large", warning_message.str(), current_time_ms()));
+        static_cast<int64_t>(state.registered_workers.size());
+    for (const auto &starting_process : state.starting_worker_processes) {
+      num_workers_started_or_registered += starting_process.second;
+    }
+    int64_t multiple = num_workers_started_or_registered / state.multiple_for_warning;
+    std::stringstream warning_message;
+    if (multiple >= 3 && multiple > state.last_warning_multiple) {
+      // Push an error message to the user if the worker pool tells us that it is
+      // getting too big.
+      state.last_warning_multiple = multiple;
+      warning_message << "WARNING: " << num_workers_started_or_registered << " "
+                      << Language_Name(entry.first)
+                      << " workers have been started. This could be a result of using "
+                      << "a large number of actors, or it could be a consequence of "
+                      << "using nested tasks "
+                      << "(see https://github.com/ray-project/ray/issues/3644) for "
+                      << "some a discussion of workarounds.";
+      RAY_CHECK_OK(gcs_client_->error_table().PushErrorToDriver(
+          JobID::Nil(), "worker_pool_large", warning_message.str(), current_time_ms()));
+    }
   }
 }
 
@@ -390,8 +429,10 @@ std::string WorkerPool::DebugString() const {
   std::stringstream result;
   result << "WorkerPool:";
   for (const auto &entry : states_by_lang_) {
-    result << "\n- num workers: " << entry.second.registered_workers.size();
-    result << "\n- num drivers: " << entry.second.registered_drivers.size();
+    result << "\n- num " << Language_Name(entry.first)
+           << " workers: " << entry.second.registered_workers.size();
+    result << "\n- num " << Language_Name(entry.first)
+           << " drivers: " << entry.second.registered_drivers.size();
   }
   return result.str();
 }
diff --git a/src/ray/raylet/worker_pool.h b/src/ray/raylet/worker_pool.h
index 4d6f4b307..fe89140f1 100644
--- a/src/ray/raylet/worker_pool.h
+++ b/src/ray/raylet/worker_pool.h
@@ -33,14 +33,12 @@ class WorkerPool {
   /// and add them to the pool.
   ///
   /// \param num_worker_processes The number of worker processes to start, per language.
-  /// \param num_workers_per_process The number of workers per process.
   /// \param maximum_startup_concurrency The maximum number of worker processes
   /// that can be started in parallel (typically this should be set to the number of CPU
   /// resources on the machine).
   /// \param worker_commands The commands used to start the worker process, grouped by
   /// language.
-  WorkerPool(int num_worker_processes, int num_workers_per_process,
-             int maximum_startup_concurrency,
+  WorkerPool(int num_worker_processes, int maximum_startup_concurrency,
              std::shared_ptr<gcs::RedisGcsClient> gcs_client,
              const WorkerCommandMap &worker_commands);
 
@@ -134,7 +132,7 @@ class WorkerPool {
  protected:
   /// Asynchronously start a new worker process. Once the worker process has
   /// registered with an external server, the process should create and
-  /// register num_workers_per_process_ workers, then add them to the pool.
+  /// register num_workers_per_process workers, then add them to the pool.
   /// Failure to start the worker process is a fatal error. If too many workers
   /// are already being started, then this function will return without starting
   /// any workers.
@@ -159,6 +157,8 @@ class WorkerPool {
   struct State {
     /// The commands and arguments used to start the worker process
     std::vector<std::string> worker_command;
+    /// The number of workers per process.
+    int num_workers_per_process;
     /// The pool of dedicated workers for actor creation tasks
     /// with prefix or suffix worker command.
     std::unordered_map<TaskID, std::shared_ptr<Worker>> idle_dedicated_workers;
@@ -179,10 +179,14 @@ class WorkerPool {
     std::unordered_map<pid_t, TaskID> dedicated_workers_to_tasks;
     /// A map for speeding up looking up the pending worker for the given task.
     std::unordered_map<TaskID, pid_t> tasks_to_dedicated_workers;
+    /// We'll push a warning to the user every time a multiple of this many
+    /// worker processes has been started.
+    int multiple_for_warning;
+    /// The last size at which a warning about the number of registered workers
+    /// was generated.
+    int64_t last_warning_multiple;
   };
 
-  /// The number of workers per process.
-  int num_workers_per_process_;
   /// Pool states per language.
   std::unordered_map<Language, State, std::hash<int>> states_by_lang_;
 
@@ -191,14 +195,8 @@ class WorkerPool {
   /// for a given language.
   State &GetStateForLanguage(const Language &language);
 
-  /// We'll push a warning to the user every time a multiple of this many
-  /// workers has been started.
-  int multiple_for_warning_;
-  /// The maximum number of workers that can be started concurrently.
+  /// The maximum number of worker processes that can be started concurrently.
   int maximum_startup_concurrency_;
-  /// The last size at which a warning about the number of registered workers
-  /// was generated.
-  int64_t last_warning_multiple_;
   /// A client connection to the GCS.
   std::shared_ptr<gcs::RedisGcsClient> gcs_client_;
 };
diff --git a/src/ray/raylet/worker_pool_test.cc b/src/ray/raylet/worker_pool_test.cc
index 34ec1619a..c3f8702b9 100644
--- a/src/ray/raylet/worker_pool_test.cc
+++ b/src/ray/raylet/worker_pool_test.cc
@@ -15,13 +15,20 @@ int MAXIMUM_STARTUP_CONCURRENCY = 5;
 class WorkerPoolMock : public WorkerPool {
  public:
   WorkerPoolMock()
-      : WorkerPoolMock({{Language::PYTHON, {"dummy_py_worker_command"}},
-                        {Language::JAVA, {"dummy_java_worker_command"}}}) {}
+      : WorkerPoolMock(
+            {{Language::PYTHON,
+              {"dummy_py_worker_command", "--foo=RAY_WORKER_NUM_WORKERS_PLACEHOLDER"}},
+             {Language::JAVA,
+              {"dummy_java_worker_command",
+               "--foo=RAY_WORKER_NUM_WORKERS_PLACEHOLDER"}}}) {}
 
   explicit WorkerPoolMock(const WorkerCommandMap &worker_commands)
-      : WorkerPool(0, NUM_WORKERS_PER_PROCESS, MAXIMUM_STARTUP_CONCURRENCY, nullptr,
-                   worker_commands),
-        last_worker_pid_(0) {}
+      : WorkerPool(0, MAXIMUM_STARTUP_CONCURRENCY, nullptr, worker_commands),
+        last_worker_pid_(0) {
+    for (auto &entry : states_by_lang_) {
+      entry.second.num_workers_per_process = NUM_WORKERS_PER_PROCESS;
+    }
+  }
 
   ~WorkerPoolMock() {
     // Avoid killing real processes
@@ -150,16 +157,38 @@ TEST_F(WorkerPoolTest, HandleWorkerRegistration) {
 }
 
 TEST_F(WorkerPoolTest, StartupWorkerCount) {
-  int desired_initial_worker_count_per_language = 20;
-  for (int i = 0; i < desired_initial_worker_count_per_language; i++) {
-    worker_pool_.StartWorkerProcess(Language::PYTHON);
-    worker_pool_.StartWorkerProcess(Language::JAVA);
+  std::string num_workers_arg =
+      std::string("--foo=") + std::to_string(NUM_WORKERS_PER_PROCESS);
+  std::vector<Language> languages = {Language::PYTHON, Language::JAVA};
+  std::vector<std::vector<std::string>> worker_commands = {
+      {{"dummy_py_worker_command", num_workers_arg},
+       {"dummy_java_worker_command", num_workers_arg}}};
+  int desired_initial_worker_process_count_per_language = MAXIMUM_STARTUP_CONCURRENCY + 1;
+  int expected_worker_process_count = MAXIMUM_STARTUP_CONCURRENCY * languages.size();
+  pid_t last_started_worker_process = 0;
+  for (int i = 0; i < desired_initial_worker_process_count_per_language; i++) {
+    for (size_t j = 0; j < languages.size(); j++) {
+      worker_pool_.StartWorkerProcess(languages[j]);
+      ASSERT_TRUE(worker_pool_.NumWorkerProcessesStarting() <=
+                  expected_worker_process_count);
+      if (last_started_worker_process != worker_pool_.LastStartedWorkerProcess()) {
+        last_started_worker_process = worker_pool_.LastStartedWorkerProcess();
+        const auto &real_command =
+            worker_pool_.GetWorkerCommand(worker_pool_.LastStartedWorkerProcess());
+        ASSERT_EQ(real_command, worker_commands[j]);
+      } else {
+        ASSERT_TRUE(worker_pool_.NumWorkerProcessesStarting() ==
+                    expected_worker_process_count);
+        ASSERT_TRUE(static_cast<int>(i * languages.size() + j) >=
+                    expected_worker_process_count);
+      }
+    }
   }
-  // Check that number of starting worker processes equals to
-  // maximum_startup_concurrency_ * 2. (because we started both python and java workers)
-  ASSERT_EQ(
-      worker_pool_.NumWorkerProcessesStarting(),
-      /* Provided in constructor of WorkerPoolMock */ MAXIMUM_STARTUP_CONCURRENCY * 2);
+  // Check number of starting worker processes
+  ASSERT_EQ(worker_pool_.NumWorkerProcessesStarting(), expected_worker_process_count);
+  ASSERT_TRUE(worker_pool_.NumWorkerProcessesStarting() <
+              static_cast<int>(desired_initial_worker_process_count_per_language *
+                               languages.size()));
 }
 
 TEST_F(WorkerPoolTest, HandleWorkerPushPop) {
@@ -232,7 +261,9 @@ TEST_F(WorkerPoolTest, PopWorkersOfMultipleLanguages) {
 
 TEST_F(WorkerPoolTest, StartWorkerWithDynamicOptionsCommand) {
   const std::vector<std::string> java_worker_command = {
-      "RAY_WORKER_OPTION_0", "dummy_java_worker_command", "RAY_WORKER_OPTION_1"};
+      "RAY_WORKER_DYNAMIC_OPTION_PLACEHOLDER_0", "dummy_java_worker_command",
+      "--foo=RAY_WORKER_NUM_WORKERS_PLACEHOLDER",
+      "RAY_WORKER_DYNAMIC_OPTION_PLACEHOLDER_1"};
   SetWorkerCommands({{Language::PYTHON, {"dummy_py_worker_command"}},
                      {Language::JAVA, java_worker_command}});
 
@@ -243,8 +274,9 @@ TEST_F(WorkerPoolTest, StartWorkerWithDynamicOptionsCommand) {
   worker_pool_.StartWorkerProcess(Language::JAVA, task_spec.DynamicWorkerOptions());
   const auto real_command =
       worker_pool_.GetWorkerCommand(worker_pool_.LastStartedWorkerProcess());
-  ASSERT_EQ(real_command, std::vector<std::string>(
-                              {"test_op_0", "dummy_java_worker_command", "test_op_1"}));
+  ASSERT_EQ(real_command,
+            std::vector<std::string>(
+                {"test_op_0", "dummy_java_worker_command", "--foo=1", "test_op_1"}));
 }
 
 }  // namespace raylet