org.apache.hadoop.yarn.event.DrainDispatcher.java Source code

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Here is the source code for org.apache.hadoop.yarn.event.DrainDispatcher.java

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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.hadoop.yarn.event;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;

@SuppressWarnings("rawtypes")
public class DrainDispatcher extends AsyncDispatcher {
    private volatile boolean drained = false;
    private final BlockingQueue<Event> queue;
    private final Object mutex;

    public DrainDispatcher() {
        this(new LinkedBlockingQueue<Event>());
    }

    public DrainDispatcher(BlockingQueue<Event> eventQueue) {
        super(eventQueue);
        this.queue = eventQueue;
        this.mutex = this;
        // Disable system exit since this class is only for unit tests.
        disableExitOnDispatchException();
    }

    /**
     *  Wait till event thread enters WAITING state (i.e. waiting for new events).
     */
    public void waitForEventThreadToWait() {
        while (!isEventThreadWaiting()) {
            Thread.yield();
        }
    }

    /**
     * Busy loop waiting for all queued events to drain.
     */
    public void await() {
        while (!isDrained()) {
            Thread.yield();
        }
    }

    @Override
    Runnable createThread() {
        return new Runnable() {
            @Override
            public void run() {
                while (!isStopped() && !Thread.currentThread().isInterrupted()) {
                    synchronized (mutex) {
                        // !drained if dispatch queued new events on this dispatcher
                        drained = queue.isEmpty();
                    }
                    Event event;
                    try {
                        event = queue.take();
                    } catch (InterruptedException ie) {
                        return;
                    }
                    if (event != null) {
                        dispatch(event);
                    }
                }
            }
        };
    }

    @SuppressWarnings("unchecked")
    @Override
    public EventHandler<Event> getEventHandler() {
        final EventHandler<Event> actual = super.getEventHandler();
        return new EventHandler<Event>() {
            @Override
            public void handle(Event event) {
                synchronized (mutex) {
                    actual.handle(event);
                    drained = false;
                }
            }
        };
    }

    @Override
    protected boolean isDrained() {
        synchronized (mutex) {
            return drained;
        }
    }
}