CountDownLatch的使用

最新推荐文章于 2025-11-06 21:12:11 发布

原创最新推荐文章于 2025-11-06 21:12:11 发布 · 198 阅读

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本文深入讲解了Java中CountDownLatch类的使用方法，演示了如何利用它来控制多个线程的同步执行，包括初始化、await和countDown方法的使用，以及在实际场景中的应用示例。

作为JDK 同步操作的一个辅助类.它可以使一个或多个线程等待,直到其他线程完成一系列的操作.初始化时会指定一个数,就是需要进行监测的线程数,每当一个纯种线程执行完毕后就-1,直到为0.

CountDownLatch的await()方法具有阻塞当前线程的作用,直到CountDownLatch减至0时再放行.

示例代码:

/*The first is a start signal that prevents any worker from proceeding until the driver is ready for them to proceed; 
The second is a completion signal that allows the driver to wait until all workers have completed. */
 
 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();            // don't let run yet
     startSignal.countDown();      // let all threads proceed
     doSomethingElse();
     doneSignal.await();           // wait for all to finish
   }
 }

 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() { ... }
 }
/*通过CountDownLatch让多个线程同时运行.类似于选手跑步的发令枪的作用
*/

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() { ... }
 }

/*多个线程同时完成一项工作时的应用场景
*/
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() { ... }
 }