/
ListenerBus.scala
82 lines (70 loc) · 2.72 KB
/
ListenerBus.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.
*/
package org.apache.spark.util
import java.util.concurrent.CopyOnWriteArrayList
import scala.collection.JavaConverters._
import scala.reflect.ClassTag
import scala.util.control.NonFatal
import org.apache.spark.internal.Logging
/**
* An event bus which posts events to its listeners.
*/
private[spark] trait ListenerBus[L <: AnyRef, E] extends Logging {
// Marked `private[spark]` for access in tests.
private[spark] val listeners = new CopyOnWriteArrayList[L]
/**
* Add a listener to listen events. This method is thread-safe and can be called in any thread.
*/
final def addListener(listener: L): Unit = {
listeners.add(listener)
}
/**
* Remove a listener and it won't receive any events. This method is thread-safe and can be called
* in any thread.
*/
final def removeListener(listener: L): Unit = {
listeners.remove(listener)
}
/**
* Post the event to all registered listeners. The `postToAll` caller should guarantee calling
* `postToAll` in the same thread for all events.
*/
def postToAll(event: E): Unit = {
// JavaConverters can create a JIterableWrapper if we use asScala.
// However, this method will be called frequently. To avoid the wrapper cost, here we use
// Java Iterator directly.
val iter = listeners.iterator
while (iter.hasNext) {
val listener = iter.next()
try {
doPostEvent(listener, event)
} catch {
case NonFatal(e) =>
logError(s"Listener ${Utils.getFormattedClassName(listener)} threw an exception", e)
}
}
}
/**
* Post an event to the specified listener. `onPostEvent` is guaranteed to be called in the same
* thread for all listeners.
*/
protected def doPostEvent(listener: L, event: E): Unit
private[spark] def findListenersByClass[T <: L : ClassTag](): Seq[T] = {
val c = implicitly[ClassTag[T]].runtimeClass
listeners.asScala.filter(_.getClass == c).map(_.asInstanceOf[T]).toSeq
}
}