线程池源码解读

深入分析java线程池的实现原理

ps:

1. 用一个AtomicInteger记录 线程池状态和其中的线程个数, 其中高3位标识线程池状态，低29位标识线程个数
2. corePoolSize -> offer进blockingQueue -> maxPoolSize
3. addWorker
   线程池中加一个worker需要先加锁
   注意Worker类的实现
4. runWorker
   getTask 从队列取task，没有就阻塞

private Runnable getTask() {
boolean timedOut = false; // Did the last poll() time out?

    for (;;) {
        int c = ctl.get();
        int rs = runStateOf(c);

        // Check if queue empty only if necessary.
        if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
            decrementWorkerCount();
            return null;
        }

        int wc = workerCountOf(c);

        // Are workers subject to culling?
        boolean timed = allowCoreThreadTimeOut || wc > corePoolSize;

        if ((wc > maximumPoolSize || (timed && timedOut))
            && (wc > 1 || workQueue.isEmpty())) {
            if (compareAndDecrementWorkerCount(c))
                return null;
            continue;
        }

        try {
            Runnable r = timed ?
                workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) :
                workQueue.take();
            if (r != null)
                return r;
            timedOut = true;
        } catch (InterruptedException retry) {
           // 阻塞时，调用shutdown() 传递一个中断信号，会执行到这里，该函数将返回null, 这样runWorker()就可以跳出循环
            timedOut = false;
        }
    }
}

5. 线程池的状态
   RUNNING： 没啥好多的
   SHUTDOWN：阻塞队列里的任务仍然会执行
   STOP： 阻塞队列里的任务全部丢弃
   可从getTask()得到验证

// Check if queue empty only if necessary.
 if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
      decrementWorkerCount();
       return null;
}
//可能写成判断
if (rs >= STOP || (rs==SHUTDOWN &&workQueue.isEmpty()))
更好理解
ps: A&&(B||C) = (A&&B)||(A&&C)