玩转并发-多线程Count Down设计模式

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。

---

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

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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();
				}
			}
		}
	}
}

测试类：

public static void main(String[] args) throws InterruptedException {
		Latch latch = new Latch(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);
						latch.countDown();
					} catch (InterruptedException e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
					}
				}
			}.start();
		}
		latch.await();
		System.out.println("阶段一全部完成，第二阶段开工");
	}

打印结果和前面例子一致。