WorkQueue.java

/*
 * Copyright (C) 2008-2016, Google Inc. and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.lib.internal;

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.ThreadFactory;

/**
 * Simple work queue to run tasks in the background
 */
public class WorkQueue {
    private static final ScheduledThreadPoolExecutor executor;

    static final Object executorKiller;

    static {
        // To support garbage collection, start our thread but
        // swap out the thread factory. When our class is GC'd
        // the executorKiller will finalize and ask the executor
        // to shutdown, ending the worker.
        //
        int threads = 1;
        executor = new ScheduledThreadPoolExecutor(threads,
                new ThreadFactory() {
                    private final ThreadFactory baseFactory = Executors
                            .defaultThreadFactory();

                    @Override
                    public Thread newThread(Runnable taskBody) {
                        Thread thr = baseFactory.newThread(taskBody);
                        thr.setName("JGit-WorkQueue"); //$NON-NLS-1$
                        thr.setContextClassLoader(null);
                        thr.setDaemon(true);
                        return thr;
                    }
                });
        executor.setRemoveOnCancelPolicy(true);
        executor.setContinueExistingPeriodicTasksAfterShutdownPolicy(false);
        executor.setExecuteExistingDelayedTasksAfterShutdownPolicy(false);
        executor.prestartAllCoreThreads();

        // Now that the threads are running, its critical to swap out
        // our own thread factory for one that isn't in the ClassLoader.
        // This allows the class to GC.
        //
        executor.setThreadFactory(Executors.defaultThreadFactory());

        executorKiller = new Object() {
            @Override
            protected void finalize() {
                executor.shutdownNow();
            }
        };
    }

    /**
     * Get the WorkQueue's executor
     *
     * @return the WorkQueue's executor
     */
    public static ScheduledThreadPoolExecutor getExecutor() {
        return executor;
    }
}