Executors的四种线程池浅析

newFixedThreadPool

//Executors.java

public static ExecutorService newFixedThreadPool(int nThreads) {

    return new ThreadPoolExecutor(nThreads, nThreads,

                0L, TimeUnit.MILLISECONDS,

                new LinkedBlockingQueue<Runnable>());

}

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指定核心线程数，队列是LinkedBlockingQueue无界阻塞队列，永远不可能拒绝任务；适合用在稳定且固定的并发场景，建议线程设置为CPU核数

newCachedThreadPool

//Executors.java

public static ExecutorService newCachedThreadPool() {

    return new ThreadPoolExecutor(0, Integer.MAX_VALUE,

                60L, TimeUnit.SECONDS,

                new SynchronousQueue<Runnable>());

}

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核心池大小为0，线程池最大线程数为最大整型，任务提交先加入到阻塞队列中，非核心线程60s没任务执行则销毁，阻塞队列为SynchronousQueue。newCachedThreadPool会不断的创建新线程来执行任务，不建议用

newScheduledThreadPool

//Executors.java

public ScheduledThreadPoolExecutor(int corePoolSize,

                                   ThreadFactory threadFactory) {

    super(corePoolSize, Integer.MAX_VALUE,

          DEFAULT_KEEPALIVE_MILLIS, MILLISECONDS,

          new DelayedWorkQueue(), threadFactory);

}

//指定延迟执行时间    

public <V> ScheduledFuture<V> 

schedule(Callable<V> callable, long delay, TimeUnit unit)    

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ScheduledThreadPoolExecutor(STPE)其实是ThreadPoolExecutor的子类，可指定核心线程数，队列是STPE的内部类DelayedWorkQueue。STPE的好处是 A 延时可执行任务，B 可执行带有返回值的任务

newSingleThreadExecutor

//Executors.java

public static ExecutorService newSingleThreadExecutor() {

    return new FinalizableDelegatedExecutorService

        (new ThreadPoolExecutor(1, 1,

                        0L, TimeUnit.MILLISECONDS,

                        new LinkedBlockingQueue<Runnable>())); //无界队列

}

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和newFixedThreadPool构造方法一致，不过线程数被设置为1了。SingleThreadExecutor比new个线程的好处是；线程运行时抛出异常的时候会有新的线程加入线程池完成接下来的任务；阻塞队列可以保证任务按FIFO执行