java 中ThreadPoolExecutor的原理是什么

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java 中ThreadPoolExecutor原理分析

线程池简介

Java线程池是开发中常用的工具，当我们有异步、并行的任务要处理时，经常会用到线程池，或者在实现一个服务器时，也需要使用线程池来接收连接处理请求。

线程池使用

jdk中提供的线程池实现位于java.util.concurrent.ThreadPoolExecutor。在使用时，通常使用ExecutorService接口，它提供了submit,invokeAll,shutdown等通用的方法。

在线程池配置方面，Executors类中提供了一些静态方法能够提供一些常用场景的线程池，如newFixedThreadPool,newCachedThreadPool,newSingleThreadExecutor等，这些方法最终都是调用到了ThreadPoolExecutor的构造函数。

ThreadPoolExecutor的包含所有参数的构造函数是

/**   * @param corePoolSize the number of threads to keep in the pool, even   *    if they are idle, unless {@code allowCoreThreadTimeOut} is set   * @param maximumPoolSize the maximum number of threads to allow in the   *    pool   * @param keepAliveTime when the number of threads is greater than   *    the core, this is the maximum time that excess idle threads   *    will wait for new tasks before terminating.   * @param unit the time unit for the {@code keepAliveTime} argument   * @param workQueue the queue to use for holding tasks before they are   *    executed. This queue will hold only the {@code Runnable}   *    tasks submitted by the {@code execute} method.   * @param threadFactory the factory to use when the executor   *    creates a new thread   * @param handler the handler to use when execution is blocked   *    because the thread bounds and queue capacities are reached  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;  }