[SPARK-3543] Write TaskContext in Java and expose it through a static accessor.

Author: Prashant Sharma <prashant.s@imaginea.com>
Author: Shashank Sharma <shashank21j@gmail.com>

Closes #2425 from ScrapCodes/SPARK-3543/withTaskContext and squashes the following commits:

8ae414c [Shashank Sharma] CR
ee8bd00 [Prashant Sharma] Added internal API in docs comments.
ddb8cbe [Prashant Sharma] Moved setting the thread local to where TaskContext is instantiated.
a7d5e23 [Prashant Sharma] Added doc comments.
edf945e [Prashant Sharma] Code review git add -A
f716fd1 [Prashant Sharma] introduced thread local for getting the task context.
333c7d6 [Prashant Sharma] Translated Task context from scala to java.

1 files changed, 274 insertions, 0 deletions

diff --git a/core/src/main/java/org/apache/spark/TaskContext.java b/core/src/main/java/org/apache/spark/TaskContext.java
new file mode 100644
index 0000000000..09b8ce02bd
--- /dev/null
+++ b/core/src/main/java/org/apache/spark/TaskContext.java
@@ -0,0 +1,274 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark;
+
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import scala.Function0;
+import scala.Function1;
+import scala.Unit;
+import scala.collection.JavaConversions;
+
+import org.apache.spark.annotation.DeveloperApi;
+import org.apache.spark.executor.TaskMetrics;
+import org.apache.spark.util.TaskCompletionListener;
+import org.apache.spark.util.TaskCompletionListenerException;
+
+/**
+* :: DeveloperApi ::
+* Contextual information about a task which can be read or mutated during execution.
+*/
+@DeveloperApi
+public class TaskContext implements Serializable {
+
+  private int stageId;
+  private int partitionId;
+  private long attemptId;
+  private boolean runningLocally;
+  private TaskMetrics taskMetrics;
+
+  /**
+   * :: DeveloperApi ::
+   * Contextual information about a task which can be read or mutated during execution.
+   *
+   * @param stageId stage id
+   * @param partitionId index of the partition
+   * @param attemptId the number of attempts to execute this task
+   * @param runningLocally whether the task is running locally in the driver JVM
+   * @param taskMetrics performance metrics of the task
+   */
+  @DeveloperApi
+  public TaskContext(Integer stageId, Integer partitionId, Long attemptId, Boolean runningLocally,
+                     TaskMetrics taskMetrics) {
+    this.attemptId = attemptId;
+    this.partitionId = partitionId;
+    this.runningLocally = runningLocally;
+    this.stageId = stageId;
+    this.taskMetrics = taskMetrics;
+  }
+
+
+  /**
+   * :: DeveloperApi ::
+   * Contextual information about a task which can be read or mutated during execution.
+   *
+   * @param stageId stage id
+   * @param partitionId index of the partition
+   * @param attemptId the number of attempts to execute this task
+   * @param runningLocally whether the task is running locally in the driver JVM
+   */
+  @DeveloperApi
+  public TaskContext(Integer stageId, Integer partitionId, Long attemptId,
+                     Boolean runningLocally) {
+    this.attemptId = attemptId;
+    this.partitionId = partitionId;
+    this.runningLocally = runningLocally;
+    this.stageId = stageId;
+    this.taskMetrics = TaskMetrics.empty();
+  }
+
+
+  /**
+   * :: DeveloperApi ::
+   * Contextual information about a task which can be read or mutated during execution.
+   *
+   * @param stageId stage id
+   * @param partitionId index of the partition
+   * @param attemptId the number of attempts to execute this task
+   */
+  @DeveloperApi
+  public TaskContext(Integer stageId, Integer partitionId, Long attemptId) {
+    this.attemptId = attemptId;
+    this.partitionId = partitionId;
+    this.runningLocally = false;
+    this.stageId = stageId;
+    this.taskMetrics = TaskMetrics.empty();
+  }
+
+  private static ThreadLocal<TaskContext> taskContext =
+    new ThreadLocal<TaskContext>();
+
+  /**
+  * :: Internal API ::
+  * This is spark internal API, not intended to be called from user programs.
+  */
+  public static void setTaskContext(TaskContext tc) {
+    taskContext.set(tc);
+  }
+
+  public static TaskContext get() {
+    return taskContext.get();
+  }
+
+  /** 
+  * :: Internal API ::
+  */
+  public static void remove() {
+    taskContext.remove();
+  }
+
+  // List of callback functions to execute when the task completes.
+  private transient List<TaskCompletionListener> onCompleteCallbacks =
+    new ArrayList<TaskCompletionListener>();
+
+  // Whether the corresponding task has been killed.
+  private volatile Boolean interrupted = false;
+
+  // Whether the task has completed.
+  private volatile Boolean completed = false;
+
+  /**
+   * Checks whether the task has completed.
+   */
+  public Boolean isCompleted() {
+    return completed;
+  }
+
+  /**
+   * Checks whether the task has been killed.
+   */
+  public Boolean isInterrupted() {
+    return interrupted;
+  }
+
+  /**
+   * Add a (Java friendly) listener to be executed on task completion.
+   * This will be called in all situation - success, failure, or cancellation.
+   * <p/>
+   * An example use is for HadoopRDD to register a callback to close the input stream.
+   */
+  public TaskContext addTaskCompletionListener(TaskCompletionListener listener) {
+    onCompleteCallbacks.add(listener);
+    return this;
+  }
+
+  /**
+   * Add a listener in the form of a Scala closure to be executed on task completion.
+   * This will be called in all situations - success, failure, or cancellation.
+   * <p/>
+   * An example use is for HadoopRDD to register a callback to close the input stream.
+   */
+  public TaskContext addTaskCompletionListener(final Function1<TaskContext, Unit> f) {
+    onCompleteCallbacks.add(new TaskCompletionListener() {
+      @Override
+      public void onTaskCompletion(TaskContext context) {
+        f.apply(context);
+      }
+    });
+    return this;
+  }
+
+  /**
+   * Add a callback function to be executed on task completion. An example use
+   * is for HadoopRDD to register a callback to close the input stream.
+   * Will be called in any situation - success, failure, or cancellation.
+   *
+   * Deprecated: use addTaskCompletionListener
+   * 
+   * @param f Callback function.
+   */
+  @Deprecated
+  public void addOnCompleteCallback(final Function0<Unit> f) {
+    onCompleteCallbacks.add(new TaskCompletionListener() {
+      @Override
+      public void onTaskCompletion(TaskContext context) {
+        f.apply();
+      }
+    });
+  }
+
+  /**
+   * ::Internal API::
+   * Marks the task as completed and triggers the listeners.
+   */
+  public void markTaskCompleted() throws TaskCompletionListenerException {
+    completed = true;
+    List<String> errorMsgs = new ArrayList<String>(2);
+    // Process complete callbacks in the reverse order of registration
+    List<TaskCompletionListener> revlist =
+      new ArrayList<TaskCompletionListener>(onCompleteCallbacks);
+    Collections.reverse(revlist);
+    for (TaskCompletionListener tcl: revlist) {
+      try {
+        tcl.onTaskCompletion(this);
+      } catch (Throwable e) {
+        errorMsgs.add(e.getMessage());
+      }
+    }
+
+    if (!errorMsgs.isEmpty()) {
+      throw new TaskCompletionListenerException(JavaConversions.asScalaBuffer(errorMsgs));
+    }
+  }
+
+  /**
+   * ::Internal API::
+   * Marks the task for interruption, i.e. cancellation.
+   */
+  public void markInterrupted() {
+    interrupted = true;
+  }
+
+  @Deprecated
+  /** Deprecated: use getStageId() */
+  public int stageId() {
+    return stageId;
+  }
+
+  @Deprecated
+  /** Deprecated: use getPartitionId() */
+  public int partitionId() {
+    return partitionId;
+  }
+
+  @Deprecated
+  /** Deprecated: use getAttemptId() */
+  public long attemptId() {
+    return attemptId;
+  }
+
+  @Deprecated
+  /** Deprecated: use getRunningLocally() */
+  public boolean runningLocally() {
+    return runningLocally;
+  }
+
+  public boolean getRunningLocally() {
+    return runningLocally;
+  }
+
+  public int getStageId() {
+    return stageId;
+  }
+
+  public int getPartitionId() {
+    return partitionId;
+  }
+
+  public long getAttemptId() {
+    return attemptId;
+  }  
+
+  /** ::Internal API:: */
+  public TaskMetrics taskMetrics() {
+    return taskMetrics;
+  }
+}