线程池

thread.png

pool.png

poolParams.png

 /**
     * Creates a new {@code ThreadPoolExecutor} with the given initial
     * parameters and default thread factory and rejected execution handler.
     * It may be more convenient to use one of the {@link Executors} factory
     * methods instead of this general purpose constructor.
     *
     * @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.
     * @throws IllegalArgumentException if one of the following holds:<br>
     *         {@code corePoolSize < 0}<br>
     *         {@code keepAliveTime < 0}<br>
     *         {@code maximumPoolSize <= 0}<br>
     *         {@code maximumPoolSize < corePoolSize}
     * @throws NullPointerException if {@code workQueue} is null
     */

如果线程数小于corePoolSize则直接创建新线程来处理任务，即使线程中的其他线程是空闲的；
如果线程池中的线程数量大于等于corePoolSize且小于*maximumPoolSize时，则只有当workQueue满的时候才创建新线程处理任务；
如果设置的corePoolSize和maximumPoolSize相同的话，那么线程池的大小是固定的，如果有新任务提交，workQueue还没满就把请求放入workQueue中等待空闲线程取出任务处理；
如果运行任务大于maximumPoolSize的时候，如果workQueue也满了则用拒绝策略

• workQueue: 处理任务有三种方式：

1. 直接切换(SynchronousBlockingQueue) 2. 有界队列(ArrayBlockingQueue) 3.无界队列(LinkedBlockingQueue)

exe.png

拒绝策略：

1. 直接抛出异常（默认）
2. 用调用者所在的线程来执行任务
   3.丢弃队列中最靠前的任务来执行当前任务
3. 直接丢弃此任务

policy.png

state.png

• Running状态：能接收新提交的任务并且也能处理阻塞队列中的任务
• Shutdown: 不能接收新提交的任务，但是可以处理阻塞队列中已经保存的任务
• STOP： 不能接收新提交的任务，也不处理队列中的任务

method.png

monitor.png

diagram.png

interface.png

config.png

juc.png