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Java:线程池(ExecutorService)使用源码说明

Java:线程池(ExecutorService)使用源码说明

作者: 々志尚 | 来源:发表于2018-08-14 11:09 被阅读0次

    转自:https://blog.csdn.net/wanghao_0206/article/details/76460877

    一、前提

    /**
    * 线程运行demo,运行时打出线程id以及传入线程中参数
    */
    public classThreadRunnerimplementsRunnable{
        private final SimpleDateFormat format = new SimpleDateFormat("HH:mm:ss.SSS");

        /**
         * 线程私有属性,创建线程时创建
         */
        private Integer num;
        public ThreadRunner(Integer num) {
            this.num = num;
        }

        @Override
        public void run() {
            System.out.println("thread:" + Thread.currentThread().getName() + ",time:" + format.format(new Date()) + ",num:" + num);

            try {//使线程睡眠,模拟线程阻塞情况
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    二、分类

    1、FixedThreadPool-有一个固定大小的线程池

    public class FixedThreadPoolDemo {
        public static void main(String[] args) {
            ExecutorService pool = Executors.newFixedThreadPool(4);
            for(int i = 0 ; i < 50 ; i++){
                pool.submit(new ThreadRunner((i + 1)));
            }
            pool.shutdown();
        }
    }

    输出:

    thread:pool-1-thread-2,time:16:14:45.677,num:2
    thread:pool-1-thread-4,time:16:14:45.678,num:4
    thread:pool-1-thread-3,time:16:14:45.680,num:3
    thread:pool-1-thread-1,time:16:14:45.684,num:1
    thread:pool-1-thread-4,time:16:14:46.680,num:5
    thread:pool-1-thread-2,time:16:14:46.680,num:6
    thread:pool-1-thread-3,time:16:14:46.680,num:7
    thread:pool-1-thread-1,time:16:14:46.684,num:8
    thread:pool-1-thread-4,time:16:14:47.680,num:9
    thread:pool-1-thread-2,time:16:14:47.680,num:10
    thread:pool-1-thread-3,time:16:14:47.681,num:11
    thread:pool-1-thread-1,time:16:14:47.684,num:12
    thread:pool-1-thread-4,time:16:14:48.681,num:13
    thread:pool-1-thread-2,time:16:14:48.681,num:14
    thread:pool-1-thread-3,time:16:14:48.681,num:15
    thread:pool-1-thread-1,time:16:14:48.684,num:16
    thread:pool-1-thread-4,time:16:14:49.681,num:17
    thread:pool-1-thread-2,time:16:14:49.682,num:18
    thread:pool-1-thread-3,time:16:14:49.682,num:19
    thread:pool-1-thread-1,time:16:14:49.684,num:20
    thread:pool-1-thread-4,time:16:14:50.681,num:21
    thread:pool-1-thread-2,time:16:14:50.682,num:22
    thread:pool-1-thread-3,time:16:14:50.682,num:23
    thread:pool-1-thread-1,time:16:14:50.684,num:24
    thread:pool-1-thread-4,time:16:14:51.681,num:25
    thread:pool-1-thread-2,time:16:14:51.682,num:26
    thread:pool-1-thread-3,time:16:14:51.682,num:27
    thread:pool-1-thread-1,time:16:14:51.684,num:28
    thread:pool-1-thread-4,time:16:14:52.681,num:29
    thread:pool-1-thread-2,time:16:14:52.682,num:30
    thread:pool-1-thread-3,time:16:14:52.682,num:31
    thread:pool-1-thread-1,time:16:14:52.684,num:32
    thread:pool-1-thread-4,time:16:14:53.681,num:33
    thread:pool-1-thread-2,time:16:14:53.682,num:34
    thread:pool-1-thread-3,time:16:14:53.683,num:35
    thread:pool-1-thread-1,time:16:14:53.685,num:36
    thread:pool-1-thread-2,time:16:14:54.682,num:38
    thread:pool-1-thread-4,time:16:14:54.682,num:37
    thread:pool-1-thread-3,time:16:14:54.683,num:39
    thread:pool-1-thread-1,time:16:14:54.686,num:40
    thread:pool-1-thread-2,time:16:14:55.682,num:41
    thread:pool-1-thread-4,time:16:14:55.682,num:42
    thread:pool-1-thread-3,time:16:14:55.683,num:43
    thread:pool-1-thread-1,time:16:14:55.686,num:44
    thread:pool-1-thread-2,time:16:14:56.682,num:45
    thread:pool-1-thread-4,time:16:14:56.683,num:46
    thread:pool-1-thread-3,time:16:14:56.684,num:47
    thread:pool-1-thread-1,time:16:14:56.686,num:48
    thread:pool-1-thread-2,time:16:14:57.683,num:49
    thread:pool-1-thread-4,time:16:14:57.683,num:50

    总结: 

    - 池中线程数量固定,不会发生变化 

    - 使用无界的LinkedBlockingQueue,要综合考虑生成与消费能力,生成过剩,可能导致堆内存溢出。 

    - 适用一些很稳定很固定的正规并发线程,多用于服务器

    2、CachedThreadPool

    public class CachedThreadPoolDemo {
        public static void main(String[] args) {
            ExecutorService pool = Executors.newCachedThreadPool();
            for(int i = 0 ; i < 50 ; i++){
                pool.submit(new ThreadRunner((i + 1)));
            }
            pool.shutdown();
        }
    }

    输出:

    thread:pool-1-thread-2,time:16:17:21.289,num:2
    thread:pool-1-thread-3,time:16:17:21.290,num:3
    thread:pool-1-thread-4,time:16:17:21.290,num:4
    thread:pool-1-thread-6,time:16:17:21.291,num:6
    thread:pool-1-thread-7,time:16:17:21.291,num:7
    thread:pool-1-thread-8,time:16:17:21.291,num:8
    thread:pool-1-thread-1,time:16:17:21.292,num:1
    thread:pool-1-thread-10,time:16:17:21.293,num:10
    thread:pool-1-thread-5,time:16:17:21.294,num:5
    thread:pool-1-thread-11,time:16:17:21.294,num:11
    thread:pool-1-thread-15,time:16:17:21.294,num:15
    thread:pool-1-thread-9,time:16:17:21.294,num:9
    thread:pool-1-thread-16,time:16:17:21.295,num:16
    thread:pool-1-thread-20,time:16:17:21.295,num:20
    thread:pool-1-thread-14,time:16:17:21.296,num:14
    thread:pool-1-thread-12,time:16:17:21.296,num:12
    thread:pool-1-thread-19,time:16:17:21.297,num:19
    thread:pool-1-thread-13,time:16:17:21.299,num:13
    thread:pool-1-thread-17,time:16:17:21.300,num:17
    thread:pool-1-thread-18,time:16:17:21.302,num:18
    thread:pool-1-thread-22,time:16:17:21.304,num:22
    thread:pool-1-thread-23,time:16:17:21.304,num:23
    thread:pool-1-thread-24,time:16:17:21.305,num:24
    thread:pool-1-thread-21,time:16:17:21.305,num:21
    thread:pool-1-thread-26,time:16:17:21.305,num:26
    thread:pool-1-thread-25,time:16:17:21.306,num:25
    thread:pool-1-thread-29,time:16:17:21.307,num:29
    thread:pool-1-thread-28,time:16:17:21.308,num:28
    thread:pool-1-thread-30,time:16:17:21.308,num:30
    thread:pool-1-thread-34,time:16:17:21.308,num:34
    thread:pool-1-thread-35,time:16:17:21.308,num:35
    thread:pool-1-thread-33,time:16:17:21.308,num:33
    thread:pool-1-thread-27,time:16:17:21.309,num:27
    thread:pool-1-thread-32,time:16:17:21.308,num:32
    thread:pool-1-thread-31,time:16:17:21.309,num:31
    thread:pool-1-thread-36,time:16:17:21.310,num:36
    thread:pool-1-thread-37,time:16:17:21.310,num:37
    thread:pool-1-thread-38,time:16:17:21.310,num:38
    thread:pool-1-thread-42,time:16:17:21.310,num:42
    thread:pool-1-thread-40,time:16:17:21.310,num:40
    thread:pool-1-thread-41,time:16:17:21.311,num:41
    thread:pool-1-thread-47,time:16:17:21.762,num:47
    thread:pool-1-thread-43,time:16:17:21.762,num:43
    thread:pool-1-thread-39,time:16:17:21.762,num:39
    thread:pool-1-thread-45,time:16:17:21.762,num:45
    thread:pool-1-thread-44,time:16:17:21.763,num:44
    thread:pool-1-thread-46,time:16:17:21.761,num:46
    thread:pool-1-thread-48,time:16:17:21.761,num:48
    thread:pool-1-thread-49,time:16:17:21.765,num:49
    thread:pool-1-thread-50,time:16:17:21.765,num:50

    总结 

    - 池中线程时随着处理数据增加而增加 

    - 线程数并不是一直增加,如果有新任务需要执行时,首先查询池中是否有空闲线程并且还为到空闲截止时间,如果有,则使用空闲线程,如果没有,则创建新线程并放入池中。 

    - 用于执行一些生存期很短的异步型任务。不适用于IO等长延时操作,因为这可能会创建大量线程,导致系统崩溃。 

    - 使用SynchronousQueue作为阻塞队列,如果有新任务进入队列,必须队列中数据被其他线程处理,否则会等待。

    3、SingleThreadExecutor

    public class SingleThreadPoolDemo {
        public static void main(String[] args) {
            ExecutorService pool = Executors.newSingleThreadExecutor();
            for(int i = 0 ; i < 50 ; i++){
                pool.submit(new ThreadRunner((i + 1)));
            }
            pool.shutdown();
        }
    }

    输出:

    thread:pool-1-thread-1,time:16:20:10.194,num:1
    thread:pool-1-thread-1,time:16:20:11.197,num:2
    thread:pool-1-thread-1,time:16:20:12.197,num:3
    thread:pool-1-thread-1,time:16:20:13.197,num:4
    thread:pool-1-thread-1,time:16:20:14.197,num:5
    thread:pool-1-thread-1,time:16:20:15.198,num:6
    thread:pool-1-thread-1,time:16:20:16.198,num:7
    thread:pool-1-thread-1,time:16:20:17.198,num:8
    thread:pool-1-thread-1,time:16:20:18.198,num:9
    thread:pool-1-thread-1,time:16:20:19.198,num:10
    thread:pool-1-thread-1,time:16:20:20.198,num:11
    thread:pool-1-thread-1,time:16:20:21.199,num:12
    thread:pool-1-thread-1,time:16:20:22.200,num:13
    thread:pool-1-thread-1,time:16:20:23.200,num:14
    thread:pool-1-thread-1,time:16:20:24.200,num:15
    thread:pool-1-thread-1,time:16:20:25.200,num:16
    thread:pool-1-thread-1,time:16:20:26.201,num:17
    thread:pool-1-thread-1,time:16:20:27.201,num:18
    thread:pool-1-thread-1,time:16:20:28.201,num:19
    thread:pool-1-thread-1,time:16:20:29.201,num:20
    thread:pool-1-thread-1,time:16:20:30.202,num:21
    thread:pool-1-thread-1,time:16:20:31.202,num:22
    thread:pool-1-thread-1,time:16:20:32.203,num:23
    thread:pool-1-thread-1,time:16:20:33.203,num:24
    thread:pool-1-thread-1,time:16:20:34.203,num:25
    thread:pool-1-thread-1,time:16:20:35.203,num:26
    thread:pool-1-thread-1,time:16:20:36.203,num:27
    thread:pool-1-thread-1,time:16:20:37.203,num:28
    thread:pool-1-thread-1,time:16:20:38.203,num:29
    thread:pool-1-thread-1,time:16:20:39.203,num:30
    thread:pool-1-thread-1,time:16:20:40.203,num:31
    thread:pool-1-thread-1,time:16:20:41.203,num:32
    thread:pool-1-thread-1,time:16:20:42.203,num:33
    thread:pool-1-thread-1,time:16:20:43.204,num:34
    thread:pool-1-thread-1,time:16:20:44.204,num:35
    thread:pool-1-thread-1,time:16:20:45.204,num:36
    thread:pool-1-thread-1,time:16:20:46.204,num:37
    thread:pool-1-thread-1,time:16:20:47.205,num:38
    thread:pool-1-thread-1,time:16:20:48.205,num:39
    thread:pool-1-thread-1,time:16:20:49.205,num:40
    thread:pool-1-thread-1,time:16:20:50.206,num:41
    thread:pool-1-thread-1,time:16:20:51.206,num:42
    thread:pool-1-thread-1,time:16:20:52.207,num:43
    thread:pool-1-thread-1,time:16:20:53.207,num:44
    thread:pool-1-thread-1,time:16:20:54.207,num:45
    thread:pool-1-thread-1,time:16:20:55.207,num:46
    thread:pool-1-thread-1,time:16:20:56.207,num:47
    thread:pool-1-thread-1,time:16:20:57.208,num:48
    thread:pool-1-thread-1,time:16:20:58.208,num:49
    thread:pool-1-thread-1,time:16:20:59.209,num:50

    总结: 

    - 线程中只有一个线程在执行 

    - 适用于有明确执行顺序但是不影响主线程的任务,压入池中的任务会按照队列顺序执行。 

    - 使用无界的LinkedBlockingQueue,要综合考虑生成与消费能力,生成过剩,可能导致堆内存溢出。

    三、源码

    public static ExecutorService newFixedThreadPool(int nThreads) {
            return new ThreadPoolExecutor(nThreads, nThreads,
                                          0L, TimeUnit.MILLISECONDS,
                                          new LinkedBlockingQueue());

    public static ExecutorService newCachedThreadPool() {
            return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                          60L, TimeUnit.SECONDS,
                                          new SynchronousQueue());

    public static ExecutorService newSingleThreadExecutor() {
            return new FinalizableDelegatedExecutorService
                (new ThreadPoolExecutor(1, 1,
                                        0L, TimeUnit.MILLISECONDS,
                                        new LinkedBlockingQueue()));
        }

    * ThreadPoolExecutor 构造方法*

    public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue workQueue) {
        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             Executors.defaultThreadFactory(), defaultHandler);
    }

    public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue workQueue,
                              ThreadFactory threadFactory,
                              RejectedExecutionHandler handler) {

        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

    corePoolSize:线程池核心线程数量 

    如果池中线程数量少于核心线程池数量,则直接新建线程处理当前任务。

    核心线程池空闲不会被回收。

    当池中无空闲线程时,新任务将被添加到阻塞队列

    maximumPoolSize:线程池最大线程数量 

    当阻塞队列已满,并且有新任务还在入队时,创建新的线程处理,直到线程数大于maximumPoolSize。

    超出corePoolSize部分的线程超过空闲时间后会被回收

    当线程已经超出corePoolSize,并且队列容量已满,则拒绝入队。

    keepAliveTime unit:线程存活时间 

    当线程超出corePoolSize时生效

    线程空余keepAliveTime后,将被回收

    workQueue:线程使用阻塞队列

    threadFactory:创建线程池工厂 

    用于控制创建线程或者销毁线程时加入其它逻辑

    handler:线程池拒绝策略 

    直接丢弃(DiscardPolicy)

    丢弃队列中最老的任务(DiscardOldestPolicy)。

    抛异常(AbortPolicy)

    将任务分给调用线程来执行(CallerRunsPolicy)

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