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(zhǔn)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(dāng)前線程不是最后一個達(dá)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(dá)到
     *  2. 一些其他的線程中斷了當(dāng)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(dāng)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(dāng)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(dāng)前線程是最后一個達(dá)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(dāng)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(yuǎn)不會進(jìn)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();
    }