二.多线程设计模式篇-2.10 Count Down设计模式

梦里梦外; 2022-12-14 08:48 163阅读 0赞

## 1.概述 ##

Count-Down设计模式其实也叫做Latch(阀门)设计模式。当若干个线程并发执行完某个特定的任务，然后等到所有的子任务都执行结束之后再统一汇总。

## 2.JDK自带CountDownLatch ##

public static void main(String[] args) throws InterruptedException {
    		//设置countdown为5
    		CountDownLatch countDownLatch = new CountDownLatch(5);
    		System.out.println("线程第一阶段开始工作");
    		
    		for(int i=0;i<5;i++) {
    			new Thread() {
    				@Override
    				public void run() {
    					try {
    						System.out.println(Thread.currentThread().getName());
    						Thread.sleep(100);
    						//计数器-1
    						countDownLatch.countDown();
    					} catch (InterruptedException e) {
    						// TODO Auto-generated catch block
    						e.printStackTrace();
    					}
    				}
    			}.start();
    		}
    		//直到计数器为0
    		countDownLatch.await();
    		System.out.println("阶段一全部完成，第二阶段开工");
    	}
    
    打印结果：
    线程第一阶段开始工作
    Thread-0
    Thread-1
    Thread-3
    Thread-2
    Thread-4
    阶段一全部完成，第二阶段开工

## 3.自定义CountDownLatch ##

public class Latch {
    	//阀门值
    	private final int latchnum;
    	
    	//计数器
    	private int count=0;
    	
    	
    	public Latch(int latchnum) {
    		this.latchnum=latchnum;
    	}
    	
    	public void countDown() {
    		synchronized (this) {
    			this.count++;
    			this.notifyAll();
    		}
    	}
    	
    	public void await() {
    		synchronized (this) {
    			if(count!=latchnum) {
    				try {
    					this.wait();
    				} catch (InterruptedException e) {
    					// TODO Auto-generated catch block
    					e.printStackTrace();
    				}
    			}
    		}
    	}
    }