深入理解Java并发工具包中的CyclicBarrier

public int await() throws InterruptedException, BrokenBarrierException {
    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 {
                // not the last thread to arrive, wait until all others arrive
                if (!trip.await(this, timeout, unit))
                    throw new TimeoutException(); // not actually in real code, for simplicity
            } catch (InterruptedException ie) {
                if (g == generation && ! g.broken) {
                    breakBarrier();
                    throw ie;
                } else {
                    // Another thread must have interrupted us; we're about to notify them
                    // and if this was our interrupt, we'll throw it again below
                    Thread.currentThread().interrupt();
                }
            }

            if (g.broken)
                throw new BrokenBarrierException();

            if (g != generation)
                return index;

            // spinning wait for next generation
            Condition r = generation.register(count = parties - 1);
            // reset count to parties on each generation change
            // yield in case we're waiting for other threads
            while (count == parties - 1)
                Thread.yield(); // spin-wait
            // arrive at new generation
            r.signalAll();
        }
    } finally {
        lock.unlock();
    }
}

// Helper methods not shown for brevity: breakBarrier(), nextGeneration(), etc.

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

public class CyclicBarrierExample {

    public static void main(String[] args) {
        // 设置屏障的阈值为3，意味着需要3个线程到达屏障后才会继续执行
        CyclicBarrier cyclicBarrier = new CyclicBarrier(3, () -> {
            System.out.println("所有线程都已到达屏障，继续执行后续任务。");
        });

        // 创建并启动3个线程，每个线程将执行不同的任务并在到达屏障时等待其他线程
        for (int i = 0; i < 3; i++) {
            new Thread(() -> {
                System.out.println(Thread.currentThread().getName() + " 开始执行任务...");
                try {
                    // 模拟执行任务的时间
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + " 任务执行完毕，等待其他线程...");
                try {
                    // 到达屏障，等待其他线程
                    cyclicBarrier.await();
                } catch (InterruptedException | BrokenBarrierException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + " 通过屏障，可以继续执行后续任务...");
            }).start();
        }
    }
}