CountDownLatch
概述
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
CountDownLatch不能重用，只能减不能加
public static void main(String[] args) 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...");
}
输出
18:44:00.778 c.TestCountDownLatch [main] - waiting...
18:44:00.778 c.TestCountDownLatch [Thread-2] - begin...
18:44:00.778 c.TestCountDownLatch [Thread-0] - begin...
18:44:00.778 c.TestCountDownLatch [Thread-1] - begin...
18:44:01.782 c.TestCountDownLatch [Thread-0] - end...2
18:44:02.283 c.TestCountDownLatch [Thread-2] - end...1
18:44:02.782 c.TestCountDownLatch [Thread-1] - end...0
18:44:02.782 c.TestCountDownLatch [main] - wait end...
可以配合线程池使用，改进如下
public static void main(String[] args) throws InterruptedException {
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();
}
});
}
应用
等待多线程准备完毕
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
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
构造方法：
public CyclicBarrier(int parties)public CyclicBarrier(int parties, Runnable barrierAction)
parties是参与线程的个数，每次调用await等待的线程数加一，直到达到parties所有线程继续运行。Runnable 参数则是可以选择计数值达到parties要做的任务。
在计数值达到parties之后，等待的线程数清零，可以重用。
CyclicBarrier cb = new CyclicBarrier(2); // 个数为2时才会继续执行
new Thread(()->{
System.out.println("线程1开始.."+new Date());
try {
cb.await(); // 当个数不足时，等待
} catch (InterruptedException | BrokenBarrierException e) {
e.printStackTrace();
}
System.out.println("线程1继续向下运行..."+new Date());
}).start();
new Thread(()->{
System.out.println("线程2开始.."+new Date());
try { Thread.sleep(2000); } catch (InterruptedException e) { }
try {
cb.await(); // 2 秒后，线程个数够2，继续运行
} catch (InterruptedException | BrokenBarrierException e) {
e.printStackTrace();
}
System.out.println("线程2继续向下运行..."+new Date());
}).start();
原创文章，作者：彭晨涛，如若转载，请注明出处：https://www.codetool.top/article/juc%e5%8c%85%e4%b8%8b%e7%9a%84%e7%ba%bf%e7%a8%8b%e5%8d%8f%e4%bd%9c%e8%ae%a1%e6%95%b0countdownlatch%e5%8f%8acyclicbarrier/
