A synchronization aid that allows one or more threads to wait until a set of operations being performed in other threads completes.

 1 import java.util.concurrent.CountDownLatch;
 2
 3 public class Teacher implements Runnable{  4  5 private CountDownLatch cdlatch;  6  7  Teacher(CountDownLatch latch){  8 this.cdlatch = latch;  9  } 10 11  @Override 12 public void run() { 13 // TODO Auto-generated method stub 14 try { 15 System.out.println("teacher is waiting..."); 16  cdlatch.await(); 17 System.out.println("teacher is collecting......"); 18 } catch (InterruptedException e) { 19 // TODO Auto-generated catch block 20  e.printStackTrace(); 21  } 22  } 23 24 }

 1 import java.util.concurrent.CountDownLatch;
 2 import java.util.concurrent.ExecutorService;  3 import java.util.concurrent.Executors;  4  5  6 public class CountDownLatchDemo {  7  8 private static int PLAYER_NUM = 10;  9 10 public static void main(String[] args) { 11 12 final CountDownLatch beginSignal = new CountDownLatch(1); 13 final CountDownLatch endSignal = new CountDownLatch(PLAYER_NUM); 14 15 ExecutorService executorService = Executors.newFixedThreadPool(PLAYER_NUM); 16 17 for(int i=0;i<PLAYER_NUM;i++){ 18 final int num = i+1; 19 Runnable runner = new Runnable(){ 20 21  @Override 22 public void run() { 23 // TODO Auto-generated method stub 24 System.out.println("No. "+num+" is waiting..."); 25 try { 26  beginSignal.await(); 27 System.out.println("No. "+num+" begin running"); 28 Thread.sleep((long) (Math.random() * 10000)); 29 System.out.println("No." + num + " arrived"); 30 } catch (InterruptedException e) { 31 // TODO Auto-generated catch block 32  e.printStackTrace(); 33 }finally{ 34  endSignal.countDown(); 35  } 36  } 37 38  }; 39  executorService.execute(runner); 40  } 41 42 System.out.println("before Game Start"); 43  beginSignal.countDown(); 44 System.out.println("Game Start"); 45 System.out.println("---In the middle of the game---"); 46 try { 47  endSignal.await(); 48 } catch (InterruptedException e) { 49 // TODO Auto-generated catch block 50  e.printStackTrace(); 51 }finally{ 52 System.out.println("Game Over!"); 53  executorService.shutdown(); 54  } 55 56  } 57 58 }

1 System.out.println("before Game Start");
2 beginSignal.countDown();
3 System.out.println("Game Start"); 4 System.out.println("---In the middle of the game---");

 1 public class TestCyclicBarrier {
 2
 3 private static final int THREAD_NUM = 5;  4  5 public static class WorkerThread implements Runnable{  6  7  CyclicBarrier barrier;  8  9 public WorkerThread(CyclicBarrier b){ 10 this.barrier = b; 11  } 12 13  @Override 14 public void run() { 15 // TODO Auto-generated method stub 16 try{ 17 System.out.println("Worker's waiting"); 18 //线程在这里等待，直到所有线程都到达barrier。 19  barrier.await(); 20 System.out.println("ID:"+Thread.currentThread().getId()+" Working"); 21 }catch(Exception e){ 22  e.printStackTrace(); 23  } 24  } 25 26  } 27 28 /** 29  * @param args 30 */ 31 public static void main(String[] args) { 32 // TODO Auto-generated method stub 33 CyclicBarrier cb = new CyclicBarrier(THREAD_NUM, new Runnable() { 34 //当所有线程到达barrier时执行 35  @Override 36 public void run() { 37 // TODO Auto-generated method stub 38 System.out.println("Inside Barrier"); 39 40  } 41  }); 42 43 for(int i=0;i<THREAD_NUM;i++){ 44 new Thread(new WorkerThread(cb)).start(); 45  } 46  } 47 48 } 49 /* 50 以下是输出： 51 Worker's waiting 52 Worker's waiting 53 Worker's waiting 54 Worker's waiting 55 Worker's waiting 56 Inside Barrier 57 ID:12 Working 58 ID:8 Working 59 ID:11 Working 60 ID:9 Working 61 ID:10 Working 62 */