org.apache.hadoop.util.AsyncDiskService.java Source code

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Here is the source code for org.apache.hadoop.util.AsyncDiskService.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.util;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;

/*
 * This class is a container of multiple thread pools, each for a volume,
 * so that we can schedule async disk operations easily.
 * 
 * Examples of async disk operations are deletion of files.
 * We can move the files to a "TO_BE_DELETED" folder before asychronously
 * deleting it, to make sure the caller can run it faster.
 */
@InterfaceAudience.LimitedPrivate({ "HDFS", "MapReduce" })
@InterfaceStability.Unstable
public class AsyncDiskService {

    public static final Log LOG = LogFactory.getLog(AsyncDiskService.class);

    // ThreadPool core pool size
    private static final int CORE_THREADS_PER_VOLUME = 1;
    // ThreadPool maximum pool size
    private static final int MAXIMUM_THREADS_PER_VOLUME = 4;
    // ThreadPool keep-alive time for threads over core pool size
    private static final long THREADS_KEEP_ALIVE_SECONDS = 60;

    private final ThreadGroup threadGroup = new ThreadGroup("async disk service");

    private ThreadFactory threadFactory;

    private HashMap<String, ThreadPoolExecutor> executors = new HashMap<String, ThreadPoolExecutor>();

    /**
     * Create a AsyncDiskServices with a set of volumes (specified by their
     * root directories).
     * 
     * The AsyncDiskServices uses one ThreadPool per volume to do the async
     * disk operations.
     * 
     * @param volumes The roots of the file system volumes.
     */
    public AsyncDiskService(String[] volumes) {

        threadFactory = new ThreadFactory() {
            @Override
            public Thread newThread(Runnable r) {
                return new Thread(threadGroup, r);
            }
        };

        // Create one ThreadPool per volume
        for (int v = 0; v < volumes.length; v++) {
            ThreadPoolExecutor executor = new ThreadPoolExecutor(CORE_THREADS_PER_VOLUME,
                    MAXIMUM_THREADS_PER_VOLUME, THREADS_KEEP_ALIVE_SECONDS, TimeUnit.SECONDS,
                    new LinkedBlockingQueue<Runnable>(), threadFactory);

            // This can reduce the number of running threads
            executor.allowCoreThreadTimeOut(true);
            executors.put(volumes[v], executor);
        }

    }

    /**
     * Execute the task sometime in the future, using ThreadPools.
     */
    public synchronized void execute(String root, Runnable task) {
        ThreadPoolExecutor executor = executors.get(root);
        if (executor == null) {
            throw new RuntimeException("Cannot find root " + root + " for execution of task " + task);
        } else {
            executor.execute(task);
        }
    }

    /**
     * Gracefully start the shut down of all ThreadPools.
     */
    public synchronized void shutdown() {

        LOG.info("Shutting down all AsyncDiskService threads...");

        for (Map.Entry<String, ThreadPoolExecutor> e : executors.entrySet()) {
            e.getValue().shutdown();
        }
    }

    /**
     * Wait for the termination of the thread pools.
     * 
     * @param milliseconds  The number of milliseconds to wait
     * @return   true if all thread pools are terminated without time limit
     * @throws InterruptedException 
     */
    public synchronized boolean awaitTermination(long milliseconds) throws InterruptedException {

        long end = Time.now() + milliseconds;
        for (Map.Entry<String, ThreadPoolExecutor> e : executors.entrySet()) {
            ThreadPoolExecutor executor = e.getValue();
            if (!executor.awaitTermination(Math.max(end - Time.now(), 0), TimeUnit.MILLISECONDS)) {
                LOG.warn("AsyncDiskService awaitTermination timeout.");
                return false;
            }
        }
        LOG.info("All AsyncDiskService threads are terminated.");
        return true;
    }

    /**
     * Shut down all ThreadPools immediately.
     */
    public synchronized List<Runnable> shutdownNow() {

        LOG.info("Shutting down all AsyncDiskService threads immediately...");

        List<Runnable> list = new ArrayList<Runnable>();
        for (Map.Entry<String, ThreadPoolExecutor> e : executors.entrySet()) {
            list.addAll(e.getValue().shutdownNow());
        }
        return list;
    }

}