java - 使用什么同步器进行线程初始化？

Question

在开始使用线程之前，我们可以使用它来初始化线程的最佳同步器是什么？

public class Worker extends Thread {

    private volatile boolean isAlive;

    @Override
    public void run() {
        isAlive = true;
        try {
            do {
                //doSomething
            } while (true);
        } finally {
            isAlive = false;
        }
    }

    public void waitForSomething() {
        if (!isAlive) {
            throw new IllegalStateException("Worker is not alive");
        }
        //something
    }

    public void waitForStartOfDoingSomething() {
        //need to wait isAlive = true.
    }
}

目前，上面的代码并不能保证方法waitForSomething在下一种情况下不会抛出IllegalStateException:

Worker worker = new Worker();
worker.start();
worker.waitForStartOfDoingSomething();
worker.waitForSomething();
//Then we let plenty of others threads to call worker.waitForSomething

我想保证上述情况下的 worker.waitForSomething() 永远不会抛出 IllegalStateException

Answer 1

您可能需要检查CountDownLatch为此目的。

private final CountDownLatch latch = new CountDownLatch(1);

public void run() {
  try {
    do {
      //doSomething
    } while (true);
  } finally {
    latch.countDown();
  }
}

public void waitForSomething() throws InterruptedException {
  latch.await();
  //something
}