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ThreadPoolExecutor使用方法

先看构造方法 ,ThreadPoolExecutor共4个构造方法:

ThreadPoolExecutor使用方法

直接看参数最多的7个参数分别代表:

public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime,  TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory,
                              RejectedExecutionHandler handler)
  • corePoolSize : 线程池核心线程数
  • maximumPoolSize :线程池最大数
  • keepAliveTime : 空闲线程存活时间
  • unit : 时间单位
  • workQueue : 线程池所使用的缓冲队列
  • threadFactory :线程池创建线程使用的工厂
  • handler : 线程池对拒绝任务的处理策略

1.当池中正在运行的线程数(包括空闲线程数)小于corePoolSize时,新建线程执行任务

 public static void main(String[] args) {
        ThreadPoolExecutor pool = new ThreadPoolExecutor(2, 3, 60L, TimeUnit.SECONDS, new LinkedBlockingQueue<>(1));
        // 任务1
        pool.execute(() -> {
            try {
                Thread.sleep(3 * 1000);
                System.out.println("--helloWorld_001--" + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        //任务2
        pool.execute(() -> System.out.println("--helloWorld_002--" + Thread.currentThread().getName()));
}

ThreadPoolExecutor使用方法

结论:线程1 结束后 没有继续线程1 而是启动线程2

2.当池中正在运行的线程数(包括空闲线程数)大于等于corePoolSize时,新插入的任务进入workQueue排队(如果workQueue长度允许),等待空闲线程来执行。

    public static void main(String[] args) {
        ThreadPoolExecutor pool = new ThreadPoolExecutor(2, 3, 60L, TimeUnit.SECONDS, new LinkedBlockingQueue<>(1));
        // 任务1
        pool.execute(() -> {
            try {
                Thread.sleep(3 * 1000);
                System.out.println("--helloWorld_001--" + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        // 任务2
        pool.execute(() -> {
            try {
                Thread.sleep(5 * 1000);
                System.out.println("--helloWorld_002--" + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        // 任务3
        pool.execute(() -> System.out.println("--helloWorld_003--" + Thread.currentThread().getName()));
}

ThreadPoolExecutor使用方法

结论:任务2在运行过程中,任务3启动不会新建线程,因为有一个队列是空的, maximumPoolSize=3 这个参数不起作用。

3.当队列里的任务达到上限,并且池中正在进行的线程小于maxinumPoolSize,对于新加入的任务,新建线程。

 public static void main(String[] args) {
        ThreadPoolExecutor pool = new ThreadPoolExecutor(2, 3, 60L, TimeUnit.SECONDS, new LinkedBlockingQueue<>(1));
        // 任务1
        pool.execute(() -> {
            try {
                Thread.sleep(3 * 1000);
                System.out.println("--helloWorld_001--" + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        // 任务2
        pool.execute(() -> {
            try {
                Thread.sleep(5 * 1000);
                System.out.println("--helloWorld_002--" + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        // 任务3
        pool.execute(() -> System.out.println("--helloWorld_003--" + Thread.currentThread().getName()));
        // 任务4
        pool.execute(() -> System.out.println("--helloWorld_004--" + Thread.currentThread().getName()));
    }

ThreadPoolExecutor使用方法

结果:任务1,2启动后 任务3在队列 ,队列就满了,由于正在进行的线程数是2<maximumPoolSize,只能新建一个线程了 然后任务4就进了新线程-3,任务4结束,队列里的任务3在线程3 进行。

4.队列里的任务达到上限,并且池中正在运行的线程等于 maximumPoolSize, 对于新加入的任务,执行拒绝策略(线程池默认的策略是抛异常)。

public static void main(String[] args) {
        ThreadPoolExecutor pool = new ThreadPoolExecutor(2, 3, 60L, TimeUnit.SECONDS, new LinkedBlockingQueue<>(1));
        // 任务1
        pool.execute(() -> {
            try {
                Thread.sleep(3 * 1000);
                System.out.println("--helloWorld_001--" + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        // 任务2
        pool.execute(() -> {
            try {
                Thread.sleep(5 * 1000);
                System.out.println("--helloWorld_002--" + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        // 任务3
        pool.execute(() -> System.out.println("--helloWorld_003--" + Thread.currentThread().getName()));
        // 任务4
        pool.execute(() -> {
            try {
                Thread.sleep(2 * 1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("--helloWorld_004--" + Thread.currentThread().getName());
        });
        // 任务5
        pool.execute(() -> System.out.println("--helloWorld_005--" + Thread.currentThread().getName()));
    }
运行结果:
Exception in thread "main" java.util.concurrent.RejectedExecutionException: Task ExecutorDemo$$Lambda$5/999966131@7699a589 rejected from java.util.concurrent.ThreadPoolExecutor@58372a00[Running, pool size = 3, active threads = 3, queued tasks = 1, completed tasks = 0]
    at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2063)
    at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:830)
    at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1379)
    at ExecutorDemo.main(ExecutorDemo.java:40)
--helloWorld_004----pool-1-thread-3
--helloWorld_003--pool-1-thread-3
--helloWorld_001--pool-1-thread-1
--helloWorld_002--pool-1-thread-2

结论:队列达到上限,线程池达到最大值,故抛出异常。

原文  http://www.cnblogs.com/xcgShare/p/11754193.html
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