CountDownLatch 减少计数

场景：多线程处理完成后统计

缺点：初始化计数量后不能调整，不适用于未知任务数的多线程作业

点击查看

        ExecutorService executorService = Executors.newFixedThreadPool(2);
        // 初始化计数数量
        CountDownLatch countDownLatch = new CountDownLatch(5);
        
        for (int i = 0; i < 5; i++) {
            System.out.println(i);
            executorService.submit(() -> {
                try {
                    Thread.sleep(3000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }finally {
                    // 线程结束时减少
                    countDownLatch.countDown();
                }
            });
        }

        try {
            // 阻塞等待减少至0
            countDownLatch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("完成");

CyclicBarrier 循环栅栏

todo

Semaphore 信号灯

todo

Phaser 移相器

CountDownLatch 的增强版，可用于不能提前确定任务总数量的情况

点击查看

    @Test
    void phaserTest() {

        ExecutorService executorService = Executors.newFixedThreadPool(2);
        Phaser phaser = new Phaser();

        for (int i = 0; i < 5; i++) {
            // 注册
            phaser.register();
            executorService.submit(() -> {
                try {
                    System.out.println(Thread.currentThread().getName());
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    // 注销
                    phaser.arriveAndDeregister();
                }

            });
        }

        // 阻塞直至所有注册注销
        phaser.arriveAndAwaitAdvance();

        System.out.println("完成");
    }

参考：理解 Java 并发工具类 Phaser - 云 + 社区 - 腾讯云 (opens new window)