并發(fā)工具類之（CountDownLatch，CyclicBarrier）

CountDownLatch

可以理解為線程的計(jì)數(shù)器骂维，使一個(gè)線程等待一組線程執(zhí)行完以后在執(zhí)行惹资，初始值為線程數(shù)的值，當(dāng)一個(gè)線程執(zhí)行完以后航闺，計(jì)數(shù)器的值減1褪测，當(dāng)計(jì)數(shù)器為0時(shí)，表示計(jì)數(shù)器上所有線程數(shù)執(zhí)行完成潦刃，開始執(zhí)行后續(xù)的任務(wù)侮措。且不支持計(jì)數(shù)器重置，當(dāng)計(jì)數(shù)器為0后乖杠，當(dāng)其他線程調(diào)await時(shí)分扎，會(huì)直接通過。

先寫個(gè)簡(jiǎn)單的例子：

@Override
    public void run(ApplicationArguments args) throws Exception{

        //創(chuàng)建固定線程數(shù)胧洒，來測(cè)試計(jì)數(shù)器的使用
        ExecutorService executorService = Executors.newFixedThreadPool(5);

        //初始化計(jì)數(shù)器
        CountDownLatch countDownLatch = new CountDownLatch(5);

        for (int i = 0; i < 5; i++) {

            Runnable runnable = new Runnable() {
                @Override
                public void run() {
                    try {
                        log.info("runnable start--> Threadname:{}",Thread.currentThread().getName());

                        Thread.sleep(1000);

                        log.info("runnable end--> Threadname:{}",Thread.currentThread().getName());
                        countDownLatch.countDown();//線程執(zhí)行完減1
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            };
            executorService.execute(runnable);
        }

        log.info("main --> 等待子線程執(zhí)行完Ｎ废拧！卫漫！");
        //獲取計(jì)數(shù)器值
        log.info("current count -->{}",countDownLatch.getCount());

        //阻塞菲饼，等待計(jì)數(shù)器執(zhí)行完

        //如果設(shè)置了超時(shí)時(shí)間，到時(shí)間會(huì)直接走下面的線程
        //countDownLatch.await(100, TimeUnit.MILLISECONDS);

        countDownLatch.await();

        log.info("main 開始執(zhí)行汛兜。巴粪。。");
        log.info("current count -->{}",countDownLatch.getCount());
    }

執(zhí)行結(jié)果：

2019-12-05 20:14:31.302  INFO 1160 --- [pool-1-thread-5] com.laod.MemcachedApplication            : runnable start--> Threadname:pool-1-thread-5
2019-12-05 20:14:31.301  INFO 1160 --- [pool-1-thread-3] com.laod.MemcachedApplication            : runnable start--> Threadname:pool-1-thread-3
2019-12-05 20:14:31.301  INFO 1160 --- [pool-1-thread-4] com.laod.MemcachedApplication            : runnable start--> Threadname:pool-1-thread-4
2019-12-05 20:14:31.302  INFO 1160 --- [           main] com.laod.MemcachedApplication            : main --> 等待子線程執(zhí)行完！８馗辫塌！
2019-12-05 20:14:31.300  INFO 1160 --- [pool-1-thread-1] com.laod.MemcachedApplication            : runnable start--> Threadname:pool-1-thread-1
2019-12-05 20:14:31.300  INFO 1160 --- [pool-1-thread-2] com.laod.MemcachedApplication            : runnable start--> Threadname:pool-1-thread-2
2019-12-05 20:14:31.302  INFO 1160 --- [           main] com.laod.MemcachedApplication            : current count -->5
2019-12-05 20:14:32.306  INFO 1160 --- [pool-1-thread-5] com.laod.MemcachedApplication            : runnable end--> Threadname:pool-1-thread-5
2019-12-05 20:14:32.306  INFO 1160 --- [pool-1-thread-2] com.laod.MemcachedApplication            : runnable end--> Threadname:pool-1-thread-2
2019-12-05 20:14:32.306  INFO 1160 --- [pool-1-thread-4] com.laod.MemcachedApplication            : runnable end--> Threadname:pool-1-thread-4
2019-12-05 20:14:32.306  INFO 1160 --- [pool-1-thread-1] com.laod.MemcachedApplication            : runnable end--> Threadname:pool-1-thread-1
2019-12-05 20:14:32.306  INFO 1160 --- [pool-1-thread-3] com.laod.MemcachedApplication            : runnable end--> Threadname:pool-1-thread-3
2019-12-05 20:14:32.307  INFO 1160 --- [           main] com.laod.MemcachedApplication            : main 開始執(zhí)行。派哲。臼氨。
2019-12-05 20:14:32.307  INFO 1160 --- [           main] com.laod.MemcachedApplication            : current count -->0

CyclicBarrier

上面的CountDownLatch，如果業(yè)務(wù)需兩個(gè)線程步調(diào)一致芭届，然后在通知其他線程储矩，雖然CountDownLatch也可以做，定義計(jì)數(shù)器2褂乍，每個(gè)線程執(zhí)行完后都減1持隧，如果計(jì)數(shù)器大于0，就線程1或者線程2等待逃片，如果計(jì)數(shù)器等于0屡拨，就喚醒線程1，線程2褥实，在執(zhí)行其他線程呀狼。

雖然這樣也可以實(shí)現(xiàn)，兩線程步調(diào)一致损离，但是較繁瑣哥艇，Java并發(fā)包內(nèi)有現(xiàn)成的可以使用：CyclicBarrier，與上面很打一個(gè)區(qū)別僻澎，這個(gè)有自動(dòng)重置貌踏，回調(diào)方法的功能，當(dāng)減到 0 的時(shí)候窟勃，會(huì)自動(dòng)重置你設(shè)置的初始值哩俭，循環(huán)執(zhí)行直接上例子：

@Override
    public void run(ApplicationArguments args) throws Exception{

        // 業(yè)務(wù)1
        Vector<String> pos = new Vector<String>();
        // 業(yè)務(wù)2
        Vector<String> dos = new Vector<String>();

        //創(chuàng)建固定線程數(shù)，來測(cè)試計(jì)數(shù)器的使用
        ExecutorService executor = Executors.newFixedThreadPool(2);

        //從字面意思就能理解 可循環(huán)利用
        CyclicBarrier barrier = new CyclicBarrier(2,() ->{
            executor.execute(()->check(pos,dos));
        });

        //業(yè)務(wù)1
        Thread T1 = new Thread(()->{
            while (1==1){
                //處理具體的業(yè)務(wù)
                try {
                    log.info("模擬業(yè)務(wù)1一直有數(shù)據(jù)");

                    pos.add("1");
                    barrier.await();

                    log.info("numberwaiting -->{}",barrier.getNumberWaiting());

                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
                    e.printStackTrace();
                }
            }
        });
        T1.start();

        //業(yè)務(wù)2
        Thread T2 = new Thread(()->{

            while (1==1){
                //處理具體的業(yè)務(wù)
                try {
                    log.info("模擬業(yè)務(wù)2一直有數(shù)據(jù)");

                    dos.add("2");
                    barrier.await();

                    log.info("numberwaiting -->{}",barrier.getNumberWaiting());

                    Thread.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
                    e.printStackTrace();
                }
            }

        });
        T2.start();
        log.debug("-----");
    }

    private void check(Vector<String> pos, Vector<String> dos) {

        pos.remove(0);
        dos.remove(0);

        log.info("--- 處理業(yè)務(wù)場(chǎng)景 步調(diào)一致");
    }

執(zhí)行結(jié)果如下拳恋，可以很清楚看到兩線程業(yè)務(wù)處理完成后，在做其他處理：

2019-12-06 09:28:02.067  INFO 1698 --- [       Thread-9] com.laod.MemcachedApplication            : 模擬業(yè)務(wù)1一直有數(shù)據(jù)
2019-12-06 09:28:02.067  INFO 1698 --- [      Thread-10] com.laod.MemcachedApplication            : 模擬業(yè)務(wù)2一直有數(shù)據(jù)
2019-12-06 09:28:02.068  INFO 1698 --- [pool-1-thread-1] com.laod.MemcachedApplication            : --- 處理業(yè)務(wù)場(chǎng)景 步調(diào)一致
2019-12-06 09:28:02.068  INFO 1698 --- [       Thread-9] com.laod.MemcachedApplication            : numberwaiting -->0
2019-12-06 09:28:02.068  INFO 1698 --- [      Thread-10] com.laod.MemcachedApplication            : numberwaiting -->0
2019-12-06 09:28:02.071  INFO 1698 --- [      Thread-10] com.laod.MemcachedApplication            : 模擬業(yè)務(wù)2一直有數(shù)據(jù)
2019-12-06 09:28:03.071  INFO 1698 --- [       Thread-9] com.laod.MemcachedApplication            : 模擬業(yè)務(wù)1一直有數(shù)據(jù)
2019-12-06 09:28:03.072  INFO 1698 --- [       Thread-9] com.laod.MemcachedApplication            : numberwaiting -->0
2019-12-06 09:28:03.072  INFO 1698 --- [      Thread-10] com.laod.MemcachedApplication            : numberwaiting -->0
2019-12-06 09:28:03.074  INFO 1698 --- [      Thread-10] com.laod.MemcachedApplication            : 模擬業(yè)務(wù)2一直有數(shù)據(jù)
2019-12-06 09:28:03.075  INFO 1698 --- [pool-1-thread-2] com.laod.MemcachedApplication            : --- 處理業(yè)務(wù)場(chǎng)景 步調(diào)一致
2019-12-06 09:28:04.077  INFO 1698 --- [       Thread-9] com.laod.MemcachedApplication            : 模擬業(yè)務(wù)1一直有數(shù)據(jù)
2019-12-06 09:28:04.077  INFO 1698 --- [      Thread-10] com.laod.MemcachedApplication            : numberwaiting -->0
2019-12-06 09:28:04.077  INFO 1698 --- [pool-1-thread-1] com.laod.MemcachedApplication            : --- 處理業(yè)務(wù)場(chǎng)景 步調(diào)一致
2019-12-06 09:28:04.077  INFO 1698 --- [       Thread-9] com.laod.MemcachedApplication            : numberwaiting -->0
2019-12-06 09:28:04.079  INFO 1698 --- [      Thread-10] com.laod.MemcachedApplication            : 模擬業(yè)務(wù)2一直有數(shù)據(jù)
2019-12-06 09:28:05.083  INFO 1698 --- [       Thread-9] com.laod.MemcachedApplication            : 模擬業(yè)務(wù)1一直有數(shù)據(jù)
2019-12-06 09:28:05.084  INFO 1698 --- [       Thread-9] com.laod.MemcachedApplication            : numberwaiting -->0
2019-12-06 09:28:05.084  INFO 1698 --- [      Thread-10] com.laod.MemcachedApplication            : numberwaiting -->0
2019-12-06 09:28:05.084  INFO 1698 --- [pool-1-thread-2] com.laod.MemcachedApplication            : --- 處理業(yè)務(wù)場(chǎng)景 步調(diào)一致
2019-12-06 09:28:05.085  INFO 1698 --- [      Thread-10] com.laod.MemcachedApplication            : 模擬業(yè)務(wù)2一直有數(shù)據(jù)
2019-12-06 09:28:06.089  INFO 1698 --- [       Thread-9] com.laod.MemcachedApplication            : 模擬業(yè)務(wù)1一直有數(shù)據(jù)
2019-12-06 09:28:06.089  INFO 1698 --- [pool-1-thread-1] com.laod.MemcachedApplication            : --- 處理業(yè)務(wù)場(chǎng)景 步調(diào)一致
2019-12-06 09:28:06.089  INFO 1698 --- [      Thread-10] com.laod.MemcachedApplication            : numberwaiting -->0
2019-12-06 09:28:06.089  INFO 1698 --- [       Thread-9] com.laod.MemcachedApplication            : numberwaiting -->0
2019-12-06 09:28:06.091  INFO 1698 --- [      Thread-10] com.laod.MemcachedApplication            : 模擬業(yè)務(wù)2一直有數(shù)據(jù)
2019-12-06 09:28:07.091  INFO 1698 --- [       Thread-9] com.laod.MemcachedApplication            : 模擬業(yè)務(wù)1一直有數(shù)據(jù)
2019-12-06 09:28:07.091  INFO 1698 --- [       Thread-9] com.laod.MemcachedApplication            : numberwaiting -->0
2019-12-06 09:28:07.091  INFO 1698 --- [      Thread-10] com.laod.MemcachedApplication            : numberwaiting -->0
2019-12-06 09:28:07.091  INFO 1698 --- [pool-1-thread-2] com.laod.MemcachedApplication            : --- 處理業(yè)務(wù)場(chǎng)景 步調(diào)一致
2019-12-06 09:28:07.092  INFO 1698 --- [      Thread-10] com.laod.MemcachedApplication            : 模擬業(yè)務(wù)2一直有數(shù)據(jù)
2019-12-06 09:28:08.096  INFO 1698 --- [       Thread-9] com.laod.MemcachedApplication            : 模擬業(yè)務(wù)1一直有數(shù)據(jù)
2019-12-06 09:28:08.096  INFO 1698 --- [      Thread-10] com.laod.MemcachedApplication            : numberwaiting -->0
2019-12-06 09:28:08.096  INFO 1698 --- [       Thread-9] com.laod.MemcachedApplication            : numberwaiting -->0
2019-12-06 09:28:08.096  INFO 1698 --- [pool-1-thread-1] com.laod.MemcachedApplication            : --- 處理業(yè)務(wù)場(chǎng)景 步調(diào)一致
2019-12-06 09:28:08.098  INFO 1698 --- [      Thread-10] com.laod.MemcachedApplication            : 模擬業(yè)務(wù)2一直有數(shù)據(jù)

總結(jié)：

CountDownLatch:
業(yè)務(wù)場(chǎng)景：一個(gè)線程等待多個(gè)線程的執(zhí)行場(chǎng)景砸捏，不能循環(huán)利用谬运，一旦計(jì)數(shù)器為0后，且有線程調(diào)用await()垦藏，會(huì)直接通過梆暖。
CyclicBarrier:
業(yè)務(wù)場(chǎng)景：一組線程之間相互等待，可循環(huán)利用掂骏，計(jì)數(shù)器為0后轰驳，會(huì)自動(dòng)重置，而且還支持回調(diào)函數(shù)。

完

最后編輯于：2019.12.06 09:49:20

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