java - 线程转储显示不正确的线程状态

Question

我正在尝试诊断生产问题。我在 Mac OS Lion 上设置了一个启动 10 个线程的小测试程序(使用 Executors.newCachedThreadPool()，它们都在同步块(synchronized block)中调用 MUTEX.wait())

然后我执行 kill -3 以获取线程转储，我看到我的所有线程都显示 BLOCKED。这些难道不应该等待吗？

代码是这样的，(请原谅为简洁而引入的代码味道)

ExecutorService executor = Executors.newCachedThreadPool();
final Object MUTEX = new Object();
for(int i = 0; i < 10; i++) {
   executor.execute(new Runnable() {
      public void run() {
        synchronized(MUTEX) {
         MUTEX.wait();
}  }   }}

此时所有线程都应该处于 WAITING 状态，但实际上线程转储显示所有线程都被阻塞

Answer 1

因为您的线程正在等待监视器锁以进入同步块(synchronized block)/方法，所以它们的状态是BLOCKED。

阻塞等待监视器锁的线程处于 BLOCKED 状态，无限期等待另一个线程执行特定操作的线程处于 WAITING > 状态。

有关 BLOCKED 和 WAITING 之间区别的更多详细信息，请参见下文:

来自 BLOCKED 的 JavaDoc :

Thread state for a thread blocked waiting for a monitor lock. A thread in the blocked state is waiting for a monitor lock to enter a synchronized block/method or reenter a synchronized block/method after calling Object.wait.

来自 WAITING 的 JavaDoc :

A thread in the waiting state is waiting for another thread to perform a particular action. For example, a thread that has called Object.wait() on an object is waiting for another thread to call Object.notify() or Object.notifyAll() on that object. A thread that has called Thread.join() is waiting for a specified thread to terminate.