java - 如何等待多个对象

Question

我有一个线程必须等待来自不同线程的多个对象。

@Override
public void run() {
    while (true) {
        for (BackgroundTask task : tasks) {
            synchronized (task) {
                if (task.isReady()) {
                    task.doTask();
                }
            }
        }
    }
}

但这是对 CPU 时间的愚蠢使用。 如何等待多个对象？

Answer 1

海事组织CountDownLatch将是解决它的好方法。引用自 Javadoc:

 class Driver2 { // ...
   void main() throws InterruptedException {
     CountDownLatch doneSignal = new CountDownLatch(N);
     Executor e = ...

     for (int i = 0; i < N; ++i) // create and start threads
       e.execute(new WorkerRunnable(doneSignal, i));

     doneSignal.await();           // wait for all to finish
   }
 }

 class WorkerRunnable implements Runnable {
   private final CountDownLatch doneSignal;
   private final int i;
   WorkerRunnable(CountDownLatch doneSignal, int i) {
      this.doneSignal = doneSignal;
      this.i = i;
   }
   public void run() {
      try {
        doWork(i);
        doneSignal.countDown();
      } catch (InterruptedException ex) {} // return;
   }

   void doWork() { ... }
 }