并发编程必须掌握的三个辅助类

CountDownLatch

倒计时计数器

countDownLatch.countDown()

countDownLatch.await()

package com.example.juc;

import java.util.concurrent.CountDownLatch;

public class TestCountDownLatch {
    public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(6);
        for (int i = 0; i < 6; i++) {
            new Thread(() -> {
                System.out.println(Thread.currentThread().getName() + "go out");
                countDownLatch.countDown();
            }, String.valueOf(i)).start();

        }
        countDownLatch.await();
        System.out.println(countDownLatch.getCount() + "over");
    }
}

结果：

0go out
5go out
4go out
2go out
3go out
1go out
0over

CyclicBarrier

简单理解为一个递增计数器

cyclicBarrier.await()

package com.example.juc;

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

public class TestCyclicBarrier {
    public static void main(String[] args) {
        CyclicBarrier cyclicBarrier = new CyclicBarrier(7, () -> {
            System.out.println("集齐七颗龙珠，召唤出神龙！");
        });

        for (int i = 1; i <= 7; i++) {
            final int temp = i;
            new Thread(() -> {
                System.out.println("收集到第" + temp + "颗");
                try {
                    cyclicBarrier.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
                    e.printStackTrace();
                }

            }).start();


        }
    }
}

结果

收集到第1颗
收集到第7颗
收集到第5颗
收集到第6颗
收集到第4颗
收集到第3颗
收集到第2颗
集齐七颗龙珠，召唤出神龙！

Semaphore

semaphore.acquire()

semaphore.release()

package com.example.juc;

import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;

public class TestSemaphore {
    public static void main(String[] args) {
        Semaphore semaphore = new Semaphore(3);
        for (int i = 1; i <= 6; i++) {
            new Thread(() -> {
                try {
                    semaphore.acquire();
                    System.out.println("第" + Thread.currentThread().getName() + "辆车停好了");
                    TimeUnit.SECONDS.sleep(2);
                    System.out.println("第" + Thread.currentThread().getName() + "辆车开走了");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    semaphore.release();
                }
            }, String.valueOf(i)).start();
        }
    }
}

第1辆车停好了
第3辆车停好了
第2辆车停好了
第2辆车开走了
第3辆车开走了
第1辆车开走了
第4辆车停好了
第6辆车停好了
第5辆车停好了
第4辆车开走了
第6辆车开走了
第5辆车开走了