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Add EventLoop and change DAGScheduler to an EventLoop
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core/src/main/scala/org/apache/spark/util/EventLoop.scala
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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. | ||
| */ | ||
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| package org.apache.spark.util | ||
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| import java.util.concurrent.{BlockingQueue, LinkedBlockingDeque} | ||
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| import scala.util.control.NonFatal | ||
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| import org.apache.spark.Logging | ||
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| /** | ||
| * An event loop to receive events from the caller and process all events in the event thread. It | ||
| * will start an exclusive event thread to process all events. | ||
| */ | ||
| abstract class EventLoop[E](name: String) extends Logging { | ||
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| private val eventQueue: BlockingQueue[E] = new LinkedBlockingDeque[E]() | ||
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| private val eventThread = new Thread(name) { | ||
| setDaemon(true) | ||
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| override def run(): Unit = { | ||
| try { | ||
| while (true) { | ||
| val event = eventQueue.take() | ||
| try { | ||
| onReceive(event) | ||
| } catch { | ||
| case NonFatal(e) => { | ||
| try { | ||
| onError(e) | ||
| } catch { | ||
| case NonFatal(e) => logError("Unexpected error in " + name, e) | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } catch { | ||
| case ie: InterruptedException => // exit even if eventQueue is not empty | ||
| case NonFatal(e) => logError("Unexpected error in " + name, e) | ||
| } | ||
| } | ||
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| } | ||
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| def start(): Unit = { | ||
| // Call onStart before starting the event thread to make sure it happens before onReceive | ||
| onStart() | ||
| eventThread.start() | ||
| } | ||
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| def stop(): Unit = { | ||
| eventThread.interrupt() | ||
| eventThread.join() | ||
| // Call onStop after the event thread exits to make sure onReceive happens before onStop | ||
| onStop() | ||
| } | ||
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| /** | ||
| * Put the event into the event queue. The event thread will process it later. | ||
| */ | ||
| def post(event: E): Unit = { | ||
| eventQueue.put(event) | ||
| } | ||
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| /** | ||
| * Return if the event thread has already been started but not yet stopped. | ||
| */ | ||
| def isActive: Boolean = eventThread.isAlive | ||
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| /** | ||
| * Invoke when `start()` is called. It's also invoked before the event thread starts. | ||
| */ | ||
| def onStart(): Unit = {} | ||
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| /** | ||
| * Invoke when `stop()` is called and the event thread exits. | ||
| */ | ||
| def onStop(): Unit = {} | ||
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| /** | ||
| * Invoke in the event thread when polling events from the event queue. | ||
| * | ||
| * Note: Should avoid calling blocking actions in `onReceive`, or the event thread will be blocked | ||
| * and cannot process events in time. If you want to call some blocking actions, run them in | ||
| * another thread. | ||
| */ | ||
| def onReceive(event: E): Unit | ||
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| /** | ||
| * Invoke if `onReceive` throws any non fatal error. `onError` must not throw any non fatal error. | ||
| */ | ||
| def onError(e: Throwable): Unit | ||
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| } |
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