ThreadPoolExecutor饱和策略

ThreadPoolExecutor线程池默认的饱和策略是 AbortPolicy

private static final RejectedExecutionHandler defaultHandler =
        new AbortPolicy();

1)CallerRunsPolicy 自己去执行该任务直接run，不会等待线程池中的线程去执行.

    public static class CallerRunsPolicy implements RejectedExecutionHandler {
        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
            if (!e.isShutdown()) {
                r.run();
            }
        }
    }

2)AbortPolicy 抛出异常RejectedExecutionException

    public static class AbortPolicy implements RejectedExecutionHandler {
        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
            throw new RejectedExecutionException("Task " + r.toString() +
                                                 " rejected from " +
                                                 e.toString());
        }
    }

3)DiscardPolicy 放弃

public static class DiscardPolicy implements RejectedExecutionHandler {
     
        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
        }
    }

4)DiscardOldestPolicy去除第一个 也就是最老的队列

    public static class DiscardOldestPolicy implements RejectedExecutionHandler {
        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
            if (!e.isShutdown()) {
                e.getQueue().poll(); //进入Deque<E> 类中的 E poll()方法;
                /*如  public E poll() {
        return pollFirst();
        }
  */ 
                e.execute(r);
            }
        }
    }

5)也可以自定义 实现RejectedExecutionHandler