advconcurrency2CyclicBarrier

1package pkg16advconcurrency;2 3import java.util.concurrent.BrokenBarrierException;4import java.util.concurrent.CyclicBarrier;5import java.util.concurrent.ExecutorService;6import java.util.concurrent.Executors;7 8/*9 * advconcurrency2CyclicBarrier.java10 * ---------------------------------11 * CyclicBarrier: N threads wait at a barrier, then all proceed together (reusable).12 *13 * DEFINITION:14 *   Unlike CountDownLatch, CyclicBarrier resets after all parties arrive. Optional15 *   barrier action runs once when the barrier trips (e.g. merge partial results).16 *17 * KEY POINTS:18 *   - await() blocks until all N parties reach the barrier.19 *   - Reusable across multiple phases (simulations, parallel merge steps).20 *   - BrokenBarrierException if a waiting thread is interrupted or times out.21 */22public class advconcurrency2CyclicBarrier {23 24    public static void main(String[] args) throws Exception {25        int parties = 3;26        CyclicBarrier barrier = new CyclicBarrier(parties, () ->27                System.out.println("  --- barrier action: all " + parties + " arrived ---"));28 29        try (ExecutorService pool = Executors.newFixedThreadPool(parties)) {30            for (int i = 0; i < parties; i++) {31                int id = i;32                pool.submit(() -> {33                    for (int phase = 1; phase <= 2; phase++) {34                        System.out.println("  thread " + id + " phase " + phase + " work");35                        try {36                            barrier.await();37                        } catch (BrokenBarrierException | InterruptedException e) {38                            Thread.currentThread().interrupt();39                            return;40                        }41                    }42                });43            }44            pool.shutdown();45            while (!pool.isTerminated()) Thread.sleep(50);46        }47        System.out.println("Done — barrier cycled twice across " + parties + " threads");48    }49}