Concurrent - CyclicBarrier

原创转载请注明出处：http://agilestyle.iteye.com/blog/2343979

 

CyclicBarrier

CyclicBarrier允许一组线程互相等待，直到到达某个公共屏障点（common barrier point），这些线程必须实时地互相等待，这种情况下就可以使用CyclicBarrier来方便地实现这样的功能。另外，CyclicBarrier的公共屏障点可以重用。

CyclicBarrierTest1.java

package org.fool.java.concurrent.cyclicbarrier;

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

public class CyclicBarrierTest1 {
    public static void main(String[] args) {
        CyclicBarrier cyclicBarrier = new CyclicBarrier(5, () -> System.out.println("All invoked!!!"));

        for (int i = 0; i < 5; i++) {
            Thread thread = new Thread(new MyThread(cyclicBarrier));
            thread.start();
        }
    }

    public static class MyThread implements Runnable {

        private CyclicBarrier cyclicBarrier;

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

        @Override
        public void run() {
            try {
                Thread.sleep((int) (Math.random() * 10000));

                System.out.println(Thread.currentThread().getName() + " invoked..." + System.currentTimeMillis());

                cyclicBarrier.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }
}

Note:

CyclicBarrier cyclicBarrier = new CyclicBarrier(5, () -> System.out.println("All invoked!!!"));

设置最大为5个parties同行者，也就是5个线程都执行了await()方法后程序才可以继续向下运行，否则这些线程彼此互相等待，一直呈阻塞状态。

 

线程个数大于parties数量进行分批处理

CyclicBarrierTest2.java

package org.fool.java.concurrent.cyclicbarrier;

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

public class CyclicBarrierTest2 {
    public static void main(String[] args) {
        try {
            CyclicBarrier cyclicBarrier = new CyclicBarrier(2, () -> System.out.println("All invoked!!!"));

            for (int i = 0; i < 4; i++) {
                Thread thread = new Thread(new MyThread(cyclicBarrier));
                thread.start();
                Thread.sleep(1000);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static class MyThread implements Runnable {

        private CyclicBarrier cyclicBarrier;

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

        @Override
        public void run() {
            try {
                System.out.println(Thread.currentThread().getName() + " begin=" + System.currentTimeMillis() + " wait 2 threads to continue");

                cyclicBarrier.await();

                System.out.println(Thread.currentThread().getName() + " end=" + System.currentTimeMillis() + " have 2 threads to continue");
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }
}

Run 

Note:

从运行结果来看，每出现2个线程就开始RUN

 

getNumberWaiting()

getNumberWaiting()作用是获得有几个线程已经到达屏障点。

CyclicBarrierTest3.java

package org.fool.java.concurrent.cyclicbarrier;

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

public class CyclicBarrierTest3 {
    public static void main(String[] args) {
        try {
            CyclicBarrier cyclicBarrier = new CyclicBarrier(3);

            for (int i = 0; i < 10; i++) {
                Thread thread = new Thread(new MyThread(cyclicBarrier));
                thread.start();
                Thread.sleep(1000);
                System.out.println(cyclicBarrier.getNumberWaiting());
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static class MyThread implements Runnable {

        private CyclicBarrier cyclicBarrier;

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

        @Override
        public void run() {
            try {
                cyclicBarrier.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }
}

Run

Note:

从运行结果来看，CyclicBarrier具有屏障重置性，也就是parties的值可以重置为0

使用CyclicBarrier屏障重置性实现多阶段的比赛实验

CyclicBarrierTest4.java

package org.fool.java.concurrent.cyclicbarrier;

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

public class CyclicBarrierTest4 {
    public static void main(String[] args) {
        CyclicBarrier cyclicBarrier = new CyclicBarrier(2);

        Service service = new Service(cyclicBarrier);

        for (int i = 0; i < 4; i++) {
            Thread thread = new Thread(new MyThread(service));
            thread.setName("Thread " + (i + 1));
            thread.start();
        }

    }

    public static class Service {
        private CyclicBarrier cyclicBarrier;

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

        public void beginRun() {
            try {
                Thread.sleep((int) (Math.random() * 10000));

                System.out.println(Thread.currentThread().getName() + " "
                        + System.currentTimeMillis() + " begin No.1 phase "
                        + (cyclicBarrier.getNumberWaiting() + 1));

                cyclicBarrier.await();

                System.out.println(Thread.currentThread().getName() + " "
                        + System.currentTimeMillis() + " end No.1 phase "
                        + (cyclicBarrier.getNumberWaiting()));

                Thread.sleep((int) (Math.random() * 10000));

                System.out.println(Thread.currentThread().getName() + " "
                        + System.currentTimeMillis() + " begin No.2 phase "
                        + (cyclicBarrier.getNumberWaiting() + 1));

                cyclicBarrier.await();

                System.out.println(Thread.currentThread().getName() + " "
                        + System.currentTimeMillis() + " end No.2 phase "
                        + (cyclicBarrier.getNumberWaiting()));
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }

    public static class MyThread implements Runnable {

        private Service service;

        public MyThread(Service service) {
            this.service = service;
        }

        @Override
        public void run() {
            service.beginRun();
        }
    }
}

Run

Note:

CyclicBarrier类的parties值从1到2，然后再恢复到0，证明CyclicBarrier类的屏障点是可以复用的，另外线程1234每到达一个屏障点时的组合是随机的，sleep勇士最少的互相组合，继续向下一个屏障行进。 

isBroken()

 

Reference

Java并发编程核心方法与框架