java - 并发性 - 为什么这个函数中的最后一条指令永远不会执行？

Question

我有这个代码:

private void doSomething() throws InterruptedException {
    WorkerThread w= new WorkerThread(this);
    w.start();
    synchronized (synchObj) {
        while (!isDone) {
            synchObj.wait();
        }
    }
    System.out.println("End");
}

调用类实现一个方法，当 WorkerThread 实例完成时，该方法会在 synchObj 上调用 notifyAll()。一切都按预期工作，除了对 System.out.println("End"); 的最终调用从未被调用。这是为什么？

编辑:这是其余的代码:

public class App implements Notifee {
    private boolean isDone = false;
    private final Object synchObj = new Object();
    /**
     * @param args
     */
    public static void main(String[] args) {
        App app = new App();
        for (int i = 0; i < 5; i++) {
            try {
                app.doSomething();
            } catch (InterruptedException e) {
                System.err.println("Didn't even start");
                e.printStackTrace();
            }
        }
    }       

    private void doSomething() throws InterruptedException {
        WorkerThread w= new WorkerThread(this);
        w.start();
        synchronized (synchObj) {
            while (!isDone) {
                synchObj.wait();
            }
        }
            System.out.println("End");
    }

    @Override
    public void letMeKnow() {
        synchronized (synchObj) {
            synchObj.notifyAll();
        }
    }       
}

public class WorkerThread extends Thread {
    private Notifee n;
    public WorkerThread(Notifee n){
        this.n = n;
    }

    @Override
    public void run() {
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        n.letMeKnow();
    }
}

Answer 1

您永远不会将 isDone 设置为 true。此外，您还应该使其 volatile 。您可能应该添加:

@Override
public void letMeKnow() {
    isDone = true;
    synchronized (synchObj) {
        synchObj.notifyAll();
    }
} 

编辑:如果您只想等待工作线程完成调用:

w.join();