Github user aarondav commented on a diff in the pull request: https://github.com/apache/spark/pull/4016#discussion_r22920216 --- Diff: core/src/main/scala/org/apache/spark/util/EventLoop.scala --- @@ -0,0 +1,110 @@ +/* + * 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.util + +import java.util.concurrent.{BlockingQueue, LinkedBlockingDeque} + +import scala.util.control.NonFatal + +import org.apache.spark.Logging + +/** + * 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 { + + private val eventQueue: BlockingQueue[E] = new LinkedBlockingDeque[E]() + + private val eventThread = new Thread(name) { + setDaemon(true) + + 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) + } + } + + } + + def start(): Unit = { + // Call onStart before starting the event thread to make sure it happens before onReceive + onStart() + eventThread.start() + } + + def stop(): Unit = { + eventThread.interrupt() + eventThread.join() + // Call onStop after the event thread exits to make sure onReceive happens before onStop + onStop() + } + + /** + * Put the event into the event queue. The event thread will process it later. + */ + def post(event: E): Unit = { + eventQueue.put(event) + } + + /** + * Return if the event thread has already been started but not yet stopped. + */ + def isActive: Boolean = eventThread.isAlive + + /** + * Invoke when `start()` is called. It's also invoked before the event thread starts. + */ + def onStart(): Unit = {} --- End diff -- Change "invoke" to "invoked" here and below; otherwise, it sounds like it is the subclass which should invoke this.
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