Java线程池（ExecutorService）使用

时间：2018-05-19 12:03:03 阅读：209 评论：0 收藏：0 [点我收藏+]

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 class ThreadRunner implements Runnable {

    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();
    }
}
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();
    }
}

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();
    }
}

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<Runnable>());
public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>());
 public static ExecutorService newSingleThreadExecutor() {
        return new FinalizableDelegatedExecutorService
            (new ThreadPoolExecutor(1, 1,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>()));
    }

ThreadPoolExecutor 构造方法*

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


 public ThreadPoolExecutor(int corePoolSize,
                          int maximumPoolSize,
                          long keepAliveTime,
                          TimeUnit unit,
                          BlockingQueue<Runnable> 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
1. 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。
2. 核心线程池空闲不会被回收。
3. 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
1. 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。
2. 超出corePoolSize部分的线程超过空闲时间后会被回收
3. 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
1. 当线程超出corePoolSize时生效
2. 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
1. 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
1. 直接丢弃（DiscardPolicy）
2. 丢弃队列中最老的任务(DiscardOldestPolicy)。
3. 抛异常(AbortPolicy)
4. 将任务分给调用线程来执行(CallerRunsPolicy)

Java线程池（ExecutorService）使用

标签：需要生效创建 void efault 添加 bsp linked 必须

原文地址：https://www.cnblogs.com/lxl57610/p/9059688.html

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