Java中的闭锁

闭锁

1.定义：

闭锁是一种同步工具，可以延迟线程直到其达到其终止状态。

例如：DOTA2中匹配等待点确定界面的设计，需要等待所有十个玩家都点就绪才能继续进行。其实也有些类似于之前CUDA编程中用到的 __syncthreads()方法去同步同一个块内的线程。

2.实现

CountDownLatch是一种灵活的闭锁实现。一般会把StartGate设置1，EndGate设置为nThreads。通过await()方法等待计数器减到0，countdown()方法执行计数器减法。

3.代码

书本TestHarness类

import java.util.concurrent.CountDownLatch;

public class TestHarness {
    public long timetasks(int nThreads, final Runnable task) throws InterruptedException {
        // init start from 1.
        final CountDownLatch startGate = new CountDownLatch(1);
        final CountDownLatch endGate = new CountDownLatch(nThreads);
        for (int i=0;i< nThreads;i++){
            Thread t = new Thread(){
                public void run(){
                    try{
                        startGate.await();//wait the startgate count down to zero, then run.
                        try{
                            task.run();
                        } finally {
                            endGate.countDown();
                        }
                    } catch (InterruptedException ignored){ }
                }
            };
            t.start();
        }
        long start = System.nanoTime(); //单位纳秒
        startGate.countDown();
        endGate.await();//wait the endGate count down to zero, then run.
        long end = System.nanoTime();
        return end - start;
    }
}

我写的测试类

public class Solution {
    public static void main(String[] args) throws InterruptedException {
        final Thread tt = new Thread(){
            @Override
            public void run() {
                System.out.println("Thread Id: " + this.getId());  //具体的方法，比如DOTA2中点击准备就绪的按键
            }
        };
        TestHarness bisuo = new TestHarness();
        long threadtime = bisuo.timetasks(100,tt);
        double ans = (double)threadtime / 1000000000;
        System.out.println("Thread time:" +ans + "s");
    }
}

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