Question

我在ThreadPoolExecutor $ Worker.runTask中找到了这样奇怪的代码

if (runState < STOP && Thread.interrupted() && runState >= STOP)
                thread.interrupt();

为什么需要检查runState < STOP和runState >= STOP。有一条评论以某种方式解释了为什么这种双重检查是必要的，但我不明白。

因此要计算表达式的最终值，它将从内存runState中获取，然后调用Thread.interrupted（）然后再从内存中获取runState（第一个runState可能与第二个不同？）并将这三个表达式的值与？

Answer 1

代码的初始目的是清除线程的interrupted状态，除非它是shuttingDownNow，所以它必须只是

if (runState < STOP)
      Thread.interrupted();

但我们有并发性。考虑两个运行代码的线程Worker：

if (runState < STOP &&
      Thread.interrupted() &&
      runState >= STOP)
    thread.interrupt();

和执行shutdownNow的线程：

if (state < STOP)
    runState = STOP;
for (Worker w : workers) {
    w.interruptNow();
}

现在这是双重检查的情况

Worker:        if (runState < STOP &&    // true for now

shutdownNow:   if (state < STOP)
shutdownNow:       runState = STOP;      // set new state
shutdownNow:   for (Worker w : workers) {
shutdownNow:       w.interruptNow();     // interrupt      
shutdownNow:   }

Worker:              Thread.interrupted() &&   // clears interrupted state 
Worker:              runState >= STOP)         // but we have double check
Worker:            thread.interrupt();         // that will setup it again

ThreadPoolExecutor $ Worker中的奇怪代码

1 个答案: