Java多线程之CountDownLatch

淡淡的烟草味﹌ 2022-06-16 08:53 234阅读 0赞

CountDownLatch犹如倒计时计数器，调用CountDownLatch对象的countDown方法就将计数器减1，当计数器为0时，则所有等待者或单个等待者开始执行。

package com.javase.thread;
    
    import java.util.Random;
    import java.util.concurrent.CountDownLatch;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    import java.util.concurrent.TimeUnit;
    import java.util.concurrent.locks.ReentrantLock;
    
    public class CountDownLatchDemo {
    	private static boolean isPrint1=true;
    	private static ReentrantLock lock = new ReentrantLock();
    	public static void main(String[] args) {
    		final CountDownLatch cdlStart = new CountDownLatch(1);
    		final CountDownLatch cdlEnd = new CountDownLatch(3);
    		ExecutorService threadPool = Executors.newCachedThreadPool();
    		for(int i=0;i<3;i++){
    			Runnable command =new Runnable(){
    				public void run() {
    					System.out.println(Thread.currentThread().getName()+" is waiting now");	
    					try {
    						cdlStart.await();
    					} catch (InterruptedException e) {
    						// TODO Auto-generated catch block
    						e.printStackTrace();
    					}
    					lock.lock();
    					try{
    						if(isPrint1){
    							System.out.println("All the 3 threads have already start to continue run ...");
    							isPrint1=false;
    						}
    					}finally{
    						lock.unlock();
    					}
    					try {
    						TimeUnit.MILLISECONDS.sleep(new Random().nextInt(5000));
    					} catch (InterruptedException e1) {
    						e1.printStackTrace();
    					}
    					cdlEnd.countDown();
    					System.out.println(Thread.currentThread().getName()+" has arrived the end ");
    				}
    			};
    			threadPool.execute(command);
    		}
    		
    		try {
    			TimeUnit.MILLISECONDS.sleep(1000);
    		} catch (InterruptedException e1) {
    			e1.printStackTrace();
    		}
    		System.out.println(Thread.currentThread().getName()+" thread send the start order ");
    		cdlStart.countDown();
    		System.out.println(Thread.currentThread().getName()+" thread is waiting for the result...");
    		try {
    			cdlEnd.await();
    		} catch (InterruptedException e) {
    			e.printStackTrace();
    		}
    		System.out.println("All the 3 threads have arrived the end ...");
    
    		threadPool.shutdown();
    
    	}
    
    }

运行结果：

pool-1-thread-1 is waiting now  
pool-1-thread-2 is waiting now  
pool-1-thread-3 is waiting now  
main thread send the start order  
main thread is waiting for the result...  
All the 3 threads have already start to continue run ...  
pool-1-thread-3 has arrived the end  
pool-1-thread-1 has arrived the end  
pool-1-thread-2 has arrived the end  
All the 3 threads have arrived the end ...