[Java] Add runtime context (#4194)

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

@@ -120,4 +120,11 @@ public final class Ray extends RayCall {
   public static RayRuntime internal() {
     return runtime;
   }
+
+  /**
+   * Get the runtime context.
+   */
+  public static RuntimeContext getRuntimeContext() {
+    return runtime.getRuntimeContext();
+  }
 }

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

@@ -0,0 +1,46 @@
+package org.ray.api;
+
+import org.ray.api.id.UniqueId;
+
+/**
+ * A class used for getting information of Ray runtime.
+ */
+public interface RuntimeContext {
+
+  /**
+   * Get the current Driver ID.
+   *
+   * If called in a driver, this returns the driver ID. If called in a worker, this returns the ID
+   * of the associated driver.
+   */
+  UniqueId getCurrentDriverId();
+
+  /**
+   * Get the current actor ID.
+   *
+   * Note, this can only be called in actors.
+   */
+  UniqueId getCurrentActorId();
+
+  /**
+   * Returns true if the current actor was reconstructed, false if it's created for the first time.
+   *
+   * Note, this method should only be called from an actor creation task.
+   */
+  boolean wasCurrentActorReconstructed();
+
+  /**
+   * Get the raylet socket name.
+   */
+  String getRayletSocketName();
+
+  /**
+   * Get the object store socket name.
+   */
+  String getObjectStoreSocketName();
+
+  /**
+   * Return true if Ray is running in single-process mode, false if Ray is running in cluster mode.
+   */
+  boolean isSingleProcess();
+}

java/api/src/main/java/org/ray/api/runtime/RayRuntime.java

@@ -3,6 +3,7 @@ package org.ray.api.runtime;
 import java.util.List;
 import org.ray.api.RayActor;
 import org.ray.api.RayObject;
+import org.ray.api.RuntimeContext;
 import org.ray.api.WaitResult;
 import org.ray.api.function.RayFunc;
 import org.ray.api.id.UniqueId;
@@ -93,4 +94,6 @@ public interface RayRuntime {
    */
   <T> RayActor<T> createActor(RayFunc actorFactoryFunc, Object[] args,
       ActorCreationOptions options);
+
+  RuntimeContext getRuntimeContext();
 }