并发常用工具

AQS ReentrantLock ReentrantReadWriteLock StampedLock Semaphore CountdownLatch CyclicBarrier UnSafe

AQS

ReentrantLock

ReentrantLock原理

ReentrantReadWriteLock

ReentrantReadWriteLock原理

StampedLock

Semaphore

CountdownLatch

用来进行线程同步协作，等待所有线程完成倒计时。

其中构造参数用来初始化等待计数值，await() 用来等待计数归零，countDown() 用来让计数减一


@Slf4j(topic = "c.TestCountDownLatch")
public class TestCountDownLatch {
    public static void main(String[] args) throws InterruptedException, ExecutionException {
        test3();
    }

    private static void test5() {
        CountDownLatch latch = new CountDownLatch(3);
        ExecutorService service = Executors.newFixedThreadPool(4);
        service.submit(() -> {
            log.debug("begin...");
            sleep(1);
            latch.countDown();
            log.debug("end...{}", latch.getCount());
        });
        service.submit(() -> {
            log.debug("begin...");
            sleep(1.5);
            latch.countDown();
            log.debug("end...{}", latch.getCount());
        });
        service.submit(() -> {
            log.debug("begin...");
            sleep(2);
            latch.countDown();
            log.debug("end...{}", latch.getCount());
        });
        service.submit(()->{
            try {
                log.debug("waiting...");
                latch.await();
                log.debug("wait end...");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
    }

    private static void test4() throws InterruptedException {
        CountDownLatch latch = new CountDownLatch(3);

        new Thread(() -> {
            log.debug("begin...");
            sleep(1);
            latch.countDown();
            log.debug("end...{}", latch.getCount());
        }).start();

        new Thread(() -> {
            log.debug("begin...");
            sleep(2);
            latch.countDown();
            log.debug("end...{}", latch.getCount());
        }).start();

        new Thread(() -> {
            log.debug("begin...");
            sleep(1.5);
            latch.countDown();
            log.debug("end...{}", latch.getCount());
        }).start();

        log.debug("waiting...");
        latch.await();
        log.debug("wait end...");
    }

    private static void test3() throws InterruptedException, ExecutionException {
        RestTemplate restTemplate = new RestTemplate();
        log.debug("begin");
        ExecutorService service = Executors.newCachedThreadPool();
        CountDownLatch latch = new CountDownLatch(4);
        Future<Map<String,Object>> f1 = service.submit(() -> {
            Map<String, Object> response = restTemplate.getForObject("http://localhost:8080/order/{1}", Map.class, 1);
            return response;
        });
        Future<Map<String, Object>> f2 = service.submit(() -> {
            Map<String, Object> response1 = restTemplate.getForObject("http://localhost:8080/product/{1}", Map.class, 1);
            return response1;
        });
        Future<Map<String, Object>> f3 = service.submit(() -> {
            Map<String, Object> response1 = restTemplate.getForObject("http://localhost:8080/product/{1}", Map.class, 2);
            return response1;
        });
        Future<Map<String, Object>> f4 = service.submit(() -> {
            Map<String, Object> response3 = restTemplate.getForObject("http://localhost:8080/logistics/{1}", Map.class, 1);
            return response3;
        });

        System.out.println(f1.get());
        System.out.println(f2.get());
        System.out.println(f3.get());
        System.out.println(f4.get());
        log.debug("执行完毕");
        service.shutdown();
    }

    private static void test2() throws InterruptedException {
        AtomicInteger num = new AtomicInteger(0);
        ExecutorService service = Executors.newFixedThreadPool(10, (r) -> {
            return new Thread(r, "t" + num.getAndIncrement());
        });
        CountDownLatch latch = new CountDownLatch(10);
        String[] all = new String[10];
        Random r = new Random();
        for (int j = 0; j < 10; j++) {
            int x = j;
            service.submit(() -> {
                for (int i = 0; i <= 100; i++) {
                    try {
                        Thread.sleep(r.nextInt(100));
                    } catch (InterruptedException e) {
                    }
                    all[x] = Thread.currentThread().getName() + "(" + (i + "%") + ")";
                    System.out.print("\r" + Arrays.toString(all));
                }
                latch.countDown();
            });
        }
        latch.await();
        System.out.println("\n游戏开始...");
        service.shutdown();
    }
}

CyclicBarrier

[ˈsaɪklɪk ˈbæriɚ] 循环栅栏，用来进行线程协作，等待线程满足某个计数。

构造时设置『计数个数』，每个线程执行到某个需要“同步”的时刻调用 await() 方法进行等待，当等待的线程数满足『计数个数』时，继续执行


@Slf4j(topic = "c.TestCyclicBarrier")
public class TestCyclicBarrier {

    public static void main(String[] args) {
        ExecutorService service = Executors.newFixedThreadPool(3);
        CyclicBarrier barrier = new CyclicBarrier(2, ()-> {
            log.debug("task1, task2 finish...");
        });
        for (int i = 0; i < 3; i++) { // task1  task2  task1
            service.submit(() -> {
                log.debug("task1 begin...");
                sleep(1);
                try {
                    barrier.await(); // 2-1=1
                } catch (InterruptedException | BrokenBarrierException e) {
                    e.printStackTrace();
                }
            });
            service.submit(() -> {
                log.debug("task2 begin...");
                sleep(2);
                try {
                    barrier.await(); // 1-1=0
                } catch (InterruptedException | BrokenBarrierException e) {
                    e.printStackTrace();
                }
            });
        }
        service.shutdown();

    }

    private static void test1() {
        ExecutorService service = Executors.newFixedThreadPool(5);
        for (int i = 0; i < 3; i++) {
            CountDownLatch latch = new CountDownLatch(2);
            service.submit(() -> {
                log.debug("task1 start...");
                sleep(1);
                latch.countDown();
            });
            service.submit(() -> {
                log.debug("task2 start...");
                sleep(2);
                latch.countDown();
            });
            try {
                latch.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            log.debug("task1 task2 finish...");
        }
        service.shutdown();
    }
}

注意 CyclicBarrier 与 CountDownLatch 的主要区别在于 CyclicBarrier 是可以重用的 CyclicBarrier 可以被比喻为『人满发车』


22:00:38.553 c.TestCyclicBarrier [pool-1-thread-2] - task2 begin...
22:00:38.553 c.TestCyclicBarrier [pool-1-thread-1] - task1 begin...
22:00:38.553 c.TestCyclicBarrier [pool-1-thread-3] - task1 begin...
22:00:39.563 c.TestCyclicBarrier [pool-1-thread-3] - task1, task2 finish...
22:00:39.563 c.TestCyclicBarrier [pool-1-thread-3] - task2 begin...
22:00:39.563 c.TestCyclicBarrier [pool-1-thread-1] - task1 begin...
22:00:40.563 c.TestCyclicBarrier [pool-1-thread-1] - task1, task2 finish...
22:00:40.563 c.TestCyclicBarrier [pool-1-thread-1] - task2 begin...
22:00:42.564 c.TestCyclicBarrier [pool-1-thread-1] - task1, task2 finish...

线程数要和栅栏数保持一致

UnSafe

Unsafe类