public CyclicBarrier(int parties, Runnable barrierAction) {
        if (parties <= 0) throw new IllegalArgumentException();
        this.parties = parties;
        this.count = parties;
        this.barrierCommand = barrierAction;
    }
    public CyclicBarrier(int parties) {
        this(parties, null);
    }

public static void main(String[] args) {
		CyclicBarrier c = new CyclicBarrier(5,new Runnable() {
			@Override
			public void run() {
				System.out.println("開始");
			}
		});
		ExecutorService es = Executors.newCachedThreadPool();
		for (int i = 0; i < 5; i++) {
			es.execute(new Task(i, c));
		}
		es.shutdown();
	}
	static public class Task implements Runnable {
		private int i;
		private CyclicBarrier cyclicBarrier;
		public Task(int i,CyclicBarrier cyclicBarrier) {
			this.i = i;
			this.cyclicBarrier = cyclicBarrier;
		}
		@Override
		public void run() {
			System.out.println(i+"準備完畢");
			try {
				cyclicBarrier.await();
				Thread.sleep(100);
				System.out.println(i+"加入了");
			} catch (InterruptedException e) {	
				e.printStackTrace();
			} catch (BrokenBarrierException e) {
				e.printStackTrace();
			}
		}
	}

    /**
     * 如果當前線程不是最后一個達到的它就會休眠直到出現(xiàn)下面的任意一種情況：
     *  1. 最后一個線程達到
     *  2. 一些其他的線程中斷了當前線程
     *  3. 一些其他的線程中斷了正在等待的線程
     *  4. 一些其他線程在等待過程中超時了
     *  5. 一些其他的線程在barrier被重置
     *  當前線程在等待的過程中如果被中斷直接會拋出異常并且當前線程的中斷狀態(tài)會被清除
     *  如果在等待的過程中一些線程被中斷,其他的等待線程就會拋出異常,barrier就會被設(shè)置成broken為true的狀態(tài)
     *  如果當前線程是最后一個達到的話,如果構(gòu)造方法中有runnable任務(wù),直接由最后一個線程去執(zhí)行,其他線程繼續(xù)等待
     *  在barrier action中,如果出現(xiàn)異常會由當前線程傳播并且barrier被設(shè)置成broken為true的狀態(tài)
     */
    public int await() throws InterruptedException, BrokenBarrierException {
        try {
            return dowait(false, 0L);
        } catch (TimeoutException toe) {
            throw new Error(toe); // 永遠不會進入catch
        }
    }

    /**
     * Main barrier code, covering the various policies.
     */
    private int dowait(boolean timed, long nanos)
        throws InterruptedException, BrokenBarrierException,
               TimeoutException {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            final Generation g = generation;
            if (g.broken)
                throw new BrokenBarrierException();
            if (Thread.interrupted()) {
                breakBarrier();
                throw new InterruptedException();
            }
            int index = --count;
            if (index == 0) {  // tripped
                boolean ranAction = false;
                try {
                    final Runnable command = barrierCommand;
                    if (command != null)
                        command.run();
                    ranAction = true;
                    nextGeneration();
                    return 0;
                } finally {
                    if (!ranAction)
                        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();
        }
    }

    private void breakBarrier() {
        generation.broken = true;
        count = parties;
        trip.signalAll();
    }

    private void nextGeneration() {
        // signal completion of last generation
        trip.signalAll();
        // set up next generation
        count = parties;
        generation = new Generation();
    }