com.pi4j.concurrent.DefaultExecutorServiceFactory Maven / Gradle / Ivy

package com.pi4j.concurrent;

/*
 * #%L
 * **********************************************************************
ORGANIZATION  :  Pi4J
PROJECT       :  Pi4J :: Java Library (Core)
FILENAME      :  DefaultExecutorServiceFactory.java

This file is part of the Pi4J project. More information about
this project can be found here:  http://www.pi4j.com/
**********************************************************************
 * %%
 * Copyright (C) 2012 - 2018 Pi4J
 * %%
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Lesser Public License for more details.
 *
 * You should have received a copy of the GNU General Lesser Public
 * License along with this program.  If not, see
 * .
 * #L%
 */


import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicLong;

public class DefaultExecutorServiceFactory implements ExecutorServiceFactory {

    private static int MAX_THREADS_IN_POOL = 25;
    private static List singleThreadExecutorServices = new ArrayList<>();

    // this seemingly odd pattern is the recommended way to lazy-initialize static fields in effective java.
    // The static "holder" class doesn't have it's static initializer called until it is accessed - and it's not accessed until the
    // getInternalScheduledExecutor() method is called.
    //
    // (see effective java item 71:Use lazy initialization judiciously)
    private static class ScheduledExecutorServiceHolder {
        static final ScheduledExecutorService heldExecutor = Executors.newScheduledThreadPool(MAX_THREADS_IN_POOL, getThreadFactory("pi4j-scheduled-executor-%d"));
    }
    private static ScheduledExecutorService getInternalScheduledExecutorService() {
        return ScheduledExecutorServiceHolder.heldExecutor;
    }
    private static class ScheduledExecutorServiceWrapperHolder {
        static final ScheduledExecutorServiceWrapper heldWrapper = new ScheduledExecutorServiceWrapper(getInternalScheduledExecutorService());
    }
    private static ScheduledExecutorServiceWrapper getScheduledExecutorServiceWrapper() {
        return ScheduledExecutorServiceWrapperHolder.heldWrapper;
    }

    // follow a similar lazy initialization pattern for the gpio events
    private static class GpioEventExecutorServiceHolder {
        static final ExecutorService heldExecutor = Executors.newCachedThreadPool(getThreadFactory("pi4j-gpio-event-executor-%d"));
    }
    private static ExecutorService getInternalGpioExecutorService() {
        return GpioEventExecutorServiceHolder.heldExecutor;
    }
    private static class GpioEventExecutorServiceWrapperHolder {
        static final ExecutorService heldWrapper = new ShutdownDisabledExecutorWrapper(getInternalGpioExecutorService());
    }
    private static ExecutorService getGpioEventExecutorServiceWrapper() {
        return GpioEventExecutorServiceWrapperHolder.heldWrapper;
    }

    /**
     * return an instance to the thread factory used to create new executor services
     */
    private static ThreadFactory getThreadFactory(final String nameFormat) {
        final ThreadFactory defaultThreadFactory = Executors.privilegedThreadFactory();
        return new ThreadFactory() {
            final AtomicLong count = (nameFormat != null) ? new AtomicLong(0) : null;

            @Override
            public Thread newThread(Runnable runnable) {
                Thread thread = defaultThreadFactory.newThread(runnable);
                if (nameFormat != null) {
                    thread.setName(String.format(nameFormat, count.getAndIncrement()));
                }
                return thread;
            }
        };
    }

    /**
     * return an instance to the scheduled executor service (wrapper)
     */
    public ScheduledExecutorService getScheduledExecutorService() {
        // we return the protected wrapper to prevent any consumers from
        // being able to shutdown the scheduled executor service
        return getScheduledExecutorServiceWrapper();
    }

    @Override
    public ExecutorService getGpioEventExecutorService() {
        // we return the protected wrapper to prevent any consumers from
        // being able to shutdown the scheduled executor service
        return getGpioEventExecutorServiceWrapper();
    }

    /**
     * return a new instance of a single thread executor service
     *
     * This method is deprecated in favor of the getGpioEventExecutorService - which provides better guarantees around resource
     * management
     */
    @Override
    public ExecutorService newSingleThreadExecutorService() {

        // create new single thread executor service
        ExecutorService singleThreadExecutorService = Executors.newSingleThreadExecutor(getThreadFactory("pi4j-single-executor-%d"));

        // add new instance to managed collection
        singleThreadExecutorServices.add(singleThreadExecutorService);

        // return new executor service
        return singleThreadExecutorService;
    }

    /**
     * shutdown executor threads
     */
    public void shutdown() {
        // shutdown each single thread executor in the managed collection
        for (ExecutorService singleThreadExecutorService : singleThreadExecutorServices) {
            shutdownExecutor(singleThreadExecutorService);
        }

        // shutdown scheduled executor instance
        shutdownExecutor(getInternalScheduledExecutorService());
        shutdownExecutor(getInternalGpioExecutorService());

    }

    private void shutdownExecutor(ExecutorService executor) {
        if (executor != null) {
            if (!executor.isShutdown()) {
                // this is a forceful shutdown;
                // don't wait for the scheduled tasks to complete
                executor.shutdownNow();
            }
        }
    }
}