Java中的CountDownLatch闭锁详解

class Driver { // ...
   void main() throws InterruptedException {
     CountDownLatch startSignal = new CountDownLatch(1);
     CountDownLatch doneSignal = new CountDownLatch(N);
     for (int i = 0; i < N; ++i) // create and start threads
       new Thread(new Worker(startSignal, doneSignal)).start();
     doSomethingElse();            // 预备工作逻辑
     startSignal.countDown();      // 让所有Worker开始工作
     doSomethingElse();
     doneSignal.await();           // 等待所有Worker完成自己逻辑
   }
 }
 class Worker implements Runnable {
   private final CountDownLatch startSignal;
   private final CountDownLatch doneSignal;
   Worker(CountDownLatch startSignal, CountDownLatch doneSignal) {
     this.startSignal = startSignal;
     this.doneSignal = doneSignal;
   }
   public void run() {
     try {
       startSignal.await();
       doWork();
       doneSignal.countDown();
     } catch (InterruptedException ex) {} // return;
   }
   void doWork() { ... }
 }

class Driver2 { // ...
   void main() throws InterruptedException {
     CountDownLatch doneSignal = new CountDownLatch(N);
     Executor e = ...
     for (int i = 0; i < N; ++i) // 创建和开启线程
       e.execute(new WorkerRunnable(doneSignal, i));
     doneSignal.await();           // 等待所有Worker完成逻辑操作
   }
 }
 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() { ... }
 }