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/*
 * 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.scheduler

import java.util.concurrent.LinkedBlockingQueue

import scala.collection.mutable.{ArrayBuffer, SynchronizedBuffer}

import org.apache.spark.Logging

/** Asynchronously passes SparkListenerEvents to registered SparkListeners. */
private[spark] class SparkListenerBus extends Logging {
  private val sparkListeners = new ArrayBuffer[SparkListener] with SynchronizedBuffer[SparkListener]

  /* Cap the capacity of the SparkListenerEvent queue so we get an explicit error (rather than
   * an OOM exception) if it's perpetually being added to more quickly than it's being drained. */
  private val EVENT_QUEUE_CAPACITY = 10000
  private val eventQueue = new LinkedBlockingQueue[SparkListenerEvents](EVENT_QUEUE_CAPACITY)
  private var queueFullErrorMessageLogged = false

  // Create a new daemon thread to listen for events. This thread is stopped when it receives
  // a SparkListenerShutdown event, using the stop method.
  new Thread("SparkListenerBus") {
    setDaemon(true)
    override def run() {
      while (true) {
        val event = eventQueue.take
        event match {
          case stageSubmitted: SparkListenerStageSubmitted =>
            sparkListeners.foreach(_.onStageSubmitted(stageSubmitted))
          case stageCompleted: SparkListenerStageCompleted =>
            sparkListeners.foreach(_.onStageCompleted(stageCompleted))
          case jobStart: SparkListenerJobStart =>
            sparkListeners.foreach(_.onJobStart(jobStart))
          case jobEnd: SparkListenerJobEnd =>
            sparkListeners.foreach(_.onJobEnd(jobEnd))
          case taskStart: SparkListenerTaskStart =>
            sparkListeners.foreach(_.onTaskStart(taskStart))
          case taskGettingResult: SparkListenerTaskGettingResult =>
            sparkListeners.foreach(_.onTaskGettingResult(taskGettingResult))
          case taskEnd: SparkListenerTaskEnd =>
            sparkListeners.foreach(_.onTaskEnd(taskEnd))
          case SparkListenerShutdown =>
            // Get out of the while loop and shutdown the daemon thread
            return
          case _ =>
        }
      }
    }
  }.start()

  def addListener(listener: SparkListener) {
    sparkListeners += listener
  }

  def post(event: SparkListenerEvents) {
    val eventAdded = eventQueue.offer(event)
    if (!eventAdded && !queueFullErrorMessageLogged) {
      logError("Dropping SparkListenerEvent because no remaining room in event queue. " +
        "This likely means one of the SparkListeners is too slow and cannot keep up with the " +
        "rate at which tasks are being started by the scheduler.")
      queueFullErrorMessageLogged = true
    }
  }

  /**
   * Waits until there are no more events in the queue, or until the specified time has elapsed.
   * Used for testing only. Returns true if the queue has emptied and false is the specified time
   * elapsed before the queue emptied.
   */
  def waitUntilEmpty(timeoutMillis: Int): Boolean = {
    val finishTime = System.currentTimeMillis + timeoutMillis
    while (!eventQueue.isEmpty) {
      if (System.currentTimeMillis > finishTime) {
        return false
      }
      /* Sleep rather than using wait/notify, because this is used only for testing and wait/notify
       * add overhead in the general case. */
      Thread.sleep(10)
    }
    return true
  }

  def stop(): Unit = post(SparkListenerShutdown)
}