Java 多线程之CyclicBarrier

参考文章：http://www.jianshu.com/p/0c2af47f98fd

import java.util.concurrent.BrokenBarrierException;import java.util.concurrent.CyclicBarrier;/** *@className CyclicBarrierTest *@description ： *       * *      CyclicBarrier是同步辅助类，它允许一组线程相互等待，直到到达某个公共屏障点。 * * *      重要属性： *          锁对象 lock            private final ReentrantLock lock = new ReentrantLock();            trip 意思是 直到出错之前的条件             private final Condition trip = lock.newCondition();                  参与者            private final int parties;            barrier将执行的任务或者命令            private final Runnable barrierCommand;            generation对象。Generation是其内部类            private Generation generation = new Generation();            private int count;   *      构造参数如下： *          CyclicBarrier(int parties);//指定了参与者数量的CyclicBarrier *          CyclicBarrier(int parties, Runnable barrierAction);//指定了参与者数量，并且当参与者都到达时，执行任务barrierAction *              if (parties <= 0) throw new IllegalArgumentException();                this.parties = parties;                this.count = parties;//将  参与者 数量赋值给count属性                this.barrierCommand = barrierAction;             * *      CyclicBarrier里面的内部类，它表示当前的CyclicBarrier是否是被损坏的。默认broken为false是完整的。 *      private static class Generation {boolean broken = false;}    * *       * *      重要方法： *      1.nextGeneration()它里面有三个操作， *          trip.signalAll();唤醒所有线程            // set up next generation            count = parties;            generation = new Generation();重新生成Generation对象 *       *      2.breakBarrier()  破坏CyclicBarrier *          generation.broken = true;            count = parties;            trip.signalAll(); *      .await(),它的内部是调用dowait(false, 0L);这里表示 不超时限制。 *           *      3.dowait(boolean timed, long nanos)这里的参数是：对于是否超时，及超时的限制。 * *      dowait的内部实现是： *          final ReentrantLock lock = this.lock;//获取到了显示锁。            lock.lock();            try {                final Generation g = generation; 获取CyclicBarrier的属性                //如果 CyclicBarrier 已损坏，就抛出异常BrokenBarrierException                if (g.broken)                    throw new BrokenBarrierException();                //如果线程中断，破坏此CyclicBarrier并且抛出InterruptedException                if (Thread.interrupted()) {                    breakBarrier();                    throw new InterruptedException();                }            //               int index = --count;  指定线程数量--               if (index == 0) {  // tripped   当index ==0 表示，所有指定的数目都已到达指定的公共屏障点                   boolean ranAction = false;                   try {                       final Runnable command = barrierCommand;//把 barrierCommand属性赋给command                       if (command != null)  如果创建对象指定barrierAction，将执行run方法                           command.run();                       ranAction = true;                       nextGeneration();//执行完之后调用nextGeneration，更新CyclicBarrier状态，并且唤醒所有线程                       return 0;                   } finally {                       if (!ranAction) //如果 未成功完成上述try中的操作，ranAction为false则会破坏此CyclicBarrier                           breakBarrier();                   }               }                // loop until tripped, broken, interrupted, or timed out                for (;;) {                    try {                        if (!timed)                            trip.await();                        else if (nanos > 0L)                            nanos = trip.awaitNanos(nanos);                    } catch (InterruptedException ie) {                        if (g == generation && ! g.broken) {                            breakBarrier();                            throw ie;                        } else {                            // We're about to finish waiting even if we had not                            // been interrupted, so this interrupt is deemed to                            // "belong" to subsequent execution.                            Thread.currentThread().interrupt();                        }                    }                    if (g.broken)                        throw new BrokenBarrierException();                    if (g != generation)                        return index;                    if (timed && nanos <= 0L) {                        breakBarrier();                        throw new TimeoutException();                    }                }            } finally {                lock.unlock();  finally释放锁，这点要注意            } *           * *@date 2017年6月15日上午9:54:03 * */public class CyclicBarrierTest {    private static CyclicBarrier cBarrier = null;    public static void main(String[] args) {        cBarrier = new CyclicBarrier(5,new Runnable() {            @Override            public void run() {                System.out.println("人到齐了，开会吧");            }        });        for(int i=0;i<5;i++){            Thread party = new PartiesThread();            /*if(i == 4){                party.interrupt();                try {                    Thread.currentThread().sleep(10000);                } catch (InterruptedException e) {                    // TODO Auto-generated catch block                    e.printStackTrace();                }            }*/            party.start();        }    }    static class PartiesThread extends Thread{        public void run(){            System.out.println(Thread.currentThread().getName()+"到了会议室");            try {                cBarrier.await();            } catch (InterruptedException | BrokenBarrierException e) {                e.printStackTrace();            }        }    }}