模仿CountDownLatch类自定义倒时计时器

Posted 2020-10-24 坏~牧羊人

简介

这里模仿CountDownLatch类自定义到时计时器，利用AQS模板中的尝试获得共享和释放共享

1、MyCountDownLatch

package com.jacky;

import com.sun.corba.se.impl.orbutil.concurrent.Sync;

import java.util.concurrent.locks.AbstractQueuedSynchronizer;

/**
 * Created by jacky on 2018/2/11.
 */
public class MyCountDownLatch {

    private final Sync sync;


    public MyCountDownLatch(int count){
        sync = new Sync(count);
    }
    static class Sync extends AbstractQueuedSynchronizer{
        public Sync(int count){
            setState(count);
        }

        /**
         * 计时器小于0的时候就会继续等待
         * @param arg
         * @return
         */
        @Override
        protected int tryAcquireShared(int arg) {
            return  getState() ==0 ?1 : -1;
        }

        @Override
        protected boolean tryReleaseShared(int arg) {
            for (;;){
                int state = getState();
                System.out.println("-------"+state+"---------");
                if (state == 0){
                    return  false;
                }
                int newState = state-1;
                if (compareAndSetState(state,newState)){
                    return newState==0;
                }
            }
        }
    }

    /**
     *state不为0就把线程挂起
     * @throws InterruptedException
     */
    public void await() throws InterruptedException {
     sync.acquireSharedInterruptibly(1);
    }

    /**
     * 倒时计时器减1
     */
    public void countDown(){
        sync.releaseShared(1);
    }

}

2、测试

package com.jacky;

import java.util.concurrent.CountDownLatch;

/**
 * Created by jacky on 2018/2/11.
 */
public class CountDownLatchDemo {

    public static void main(String[] args) {
        Thread mainThread = Thread.currentThread();
        //CountDownLatch latch = new CountDownLatch(4);
        MyCountDownLatch latch = new MyCountDownLatch(4);
        Runnable runnable = new Runnable() {

            @Override
            public void run() {
                try {
                    Thread.sleep((int)(Math.random()*100));

                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("currentThread--"+Thread.currentThread().getName()+"--mainThread--"+mainThread.getName()
                +"--mainThreadStatus--"+mainThread.getState());
                latch.countDown();
            }
        };
        Thread thread1 = new Thread(runnable);
        Thread thread2 = new Thread(runnable);
        Thread thread3 = new Thread(runnable);
        Thread thread4 = new Thread(runnable);
        thread1.start();
        thread2.start();
        thread3.start();
        thread4.start();
        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("mainThread end");
    }
}