J.U.C工具包之CyclicBarrier

技术2020年8月4日

什么是CyclicBarrier：

CyclicBarrier可以在构造时指定需要在屏障前执行await的个数，所有对await的调用都会等待,直到调用await的次数达到预定指，所有等待都会立即被唤醒。

从使用场景上来说，CyclicBarrier是让多个线程互相等待某一事件的发生，然后同时被唤醒。而CountDownLatch是让某一线程等待多个线程的状态，然后该线程被唤醒。

例子：

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

public class CyclicBarrierDemo {
    public static void main(String[] args) throws InterruptedException {
        new CyclicBarrierDemo().test();
    }

    private void test() throws InterruptedException {
        CyclicBarrier cyclicBarrier = new CyclicBarrier(3);
        new Thread(new Task(cyclicBarrier), "Thread1").start();
        Thread.sleep(1000);
        new Thread(new Task(cyclicBarrier), "Thread2").start();
        Thread.sleep(1000);
        new Thread(new Task(cyclicBarrier), "Thread3").start();
    }

    class Task implements Runnable {
        private CyclicBarrier cyclicBarrier;

        public Task(CyclicBarrier cyclicBarrier) {
            this.cyclicBarrier = cyclicBarrier;
        }

        @Override
        public void run() {
            System.out
                .println("Thread:" + Thread.currentThread().getName() + " starttime:" + System.currentTimeMillis());
            try {
                cyclicBarrier.await();
            } catch (InterruptedException | BrokenBarrierException e) {
                e.printStackTrace();
            }
            System.out
                .println("Thread:" + Thread.currentThread().getName() + " start process:" + System.currentTimeMillis());
        }
    }
}

import java.util.concurrent.BrokenBarrierException;

import java.util.concurrent.CyclicBarrier;

public class CyclicBarrierDemo {

public static void main(String[] args) throws InterruptedException {

new CyclicBarrierDemo().test();

}

private void test() throws InterruptedException {

CyclicBarrier cyclicBarrier = new CyclicBarrier(3);

new Thread(new Task(cyclicBarrier), "Thread1").start();

Thread.sleep(1000);

new Thread(new Task(cyclicBarrier), "Thread2").start();

Thread.sleep(1000);

new Thread(new Task(cyclicBarrier), "Thread3").start();

}

class Task implements Runnable {

private CyclicBarrier cyclicBarrier;

public Task(CyclicBarrier cyclicBarrier) {

this.cyclicBarrier = cyclicBarrier;

}

@Override

public void run() {

System.out

.println("Thread:" + Thread.currentThread().getName() + " starttime:" + System.currentTimeMillis());

try {

cyclicBarrier.await();

} catch (InterruptedException | BrokenBarrierException e) {

e.printStackTrace();

}

System.out

.println("Thread:" + Thread.currentThread().getName() + " start process:" + System.currentTimeMillis());

}

执行结果：

Thread:Thread1 starttime:1596530849984
Thread:Thread2 starttime:1596530850984
Thread:Thread3 starttime:1596530851985
/**这里所有线程未执行完成，均在等待计数为0后才完成后续执行*/
Thread:Thread3 start process:1596530851985
Thread:Thread1 start process:1596530851985
Thread:Thread2 start process:1596530851985

Thread:Thread1 starttime:1596530849984

Thread:Thread2 starttime:1596530850984

Thread:Thread3 starttime:1596530851985

/**这里所有线程未执行完成，均在等待计数为0后才完成后续执行*/

Thread:Thread3 start process:1596530851985

Thread:Thread1 start process:1596530851985

Thread:Thread2 start process:1596530851985

J.U.C工具包之CyclicBarrier

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