多线程的CountDown设计模式

场景：控制逻辑按步骤执行

Doug Lea的CountDownLatch实现方式

package com.dwz.concurrency2.chapter15;

import java.util.Random;
import java.util.concurrent.CountDownLatch;
import java.util.stream.IntStream;

public class JDKCountDown {
    private final static Random random = new Random(System.currentTimeMillis());
    
    public static void main(String[] args) throws InterruptedException {
        final CountDownLatch latch = new CountDownLatch(5);
        
        System.out.println("准备多线程处理任务。。。");
        //第一步
        IntStream.rangeClosed(1, 5).forEach(i -> {
            new Thread(() -> {
                System.out.println(Thread.currentThread().getName() + " is working.");
                try {
                    Thread.sleep(random.nextInt(1000));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                //标记结束
                latch.countDown();
            }, String.valueOf(i)).start();
        });
        
        //在等待所有任务结束
        latch.await();
        //第二步
        System.out.println("多线程任务全部结束，准备第二阶段任务");
        System.out.println("...................");
        System.out.println("FINISH");
    }
}

自定义一个CountDown

package com.dwz.concurrency2.chapter15;

public class CountDown {
    private final int total;
    private int counter = 0;
    
    public CountDown(int total) {
        this.total = total;
    }
    
    public void down() {
        synchronized (this) {
            this.counter++;
            this.notifyAll();
        }
    }
    
    public void await() throws InterruptedException {
        synchronized (this) {
            while (counter != total) {
                this.wait();
            }
        }
    }
}

测试自定义CountDown

package com.dwz.concurrency2.chapter15;

import java.util.Random;
import java.util.concurrent.CountDownLatch;
import java.util.stream.IntStream;

public class CustomCountDown {
    private final static Random random = new Random(System.currentTimeMillis());
    
    public static void main(String[] args) throws InterruptedException {
        final CountDown latch = new CountDown(5);
        System.out.println("准备多线程处理任务。。。");
        //第一步
        IntStream.rangeClosed(1, 5).forEach(i -> {
            new Thread(() -> {
                System.out.println(Thread.currentThread().getName() + " is working.");
                try {
                    Thread.sleep(random.nextInt(1000));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                //标记结束
                latch.down();
            }, String.valueOf(i)).start();
        });
        
        //在等待所有任务结束
        latch.await();
        //第二步
        System.out.println("多线程任务全部结束，准备第二阶段任务");
        System.out.println("...................");
        System.out.println("FINISH");
    }


}

测试结果：

准备多线程处理任务。。。
2 is working.
4 is working.
1 is working.
3 is working.
5 is working.
多线程任务全部结束，准备第二阶段任务
...................
FINISH