java线程 - 同步工具类

目录

一. 闭锁（CountDownLatch）

二. 栅栏( CyclicBarrier )

三. 信号量（Semaphore）

四. Exchanger

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一. 闭锁（CountDownLatch）

1. 设计原理：一个线程或者一组线程等待其他线程完成之后，再继续运行。不可重用。计数值减一。
2. 应用场景： 

               （1） 一个资源需要初始化才能使用，然后需要这个资源的操作都需要等待该资源初始化。

               （2）某个服务在其依赖的服务启动之后再进行启动。

               （3）等待所有的参与者准备就绪再进行执行。

    3.  demo：

package com.test.countdownlatch;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.TimeUnit;

public class CountDownLatchDemo {

    public static void main(String[] args) {
        long executeTime = task(10, new Runnable() {
            @Override
            public void run() {
                try {
                    System.out.println(Thread.currentThread().getName() + "准备就绪");
                    TimeUnit.SECONDS.sleep(ThreadLocalRandom.current().nextInt(5));
                    System.out.println(Thread.currentThread().getName() + "完成比赛");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        System.out.println("比赛用时:"+ executeTime + "ms");
    }

    public static long task(int threadNum, Runnable runnable) {
        CountDownLatch latch1 = new CountDownLatch(1);
        CountDownLatch latch2 = new CountDownLatch(10);
        for (int i = 0; i < threadNum; i++) {
            new Thread(() -> {
                try {
                    latch1.await();
                    try {
                        runnable.run();
                    } finally {
                        latch2.countDown();
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }).start();
        }
        long startTime = System.currentTimeMillis();
        latch1.countDown();
        try {
            latch2.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        long endTime = System.currentTimeMillis();
        System.out.println("比赛结束");
        return endTime - startTime;
    }
}

 

二. 栅栏( CyclicBarrier )

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1. 设计原理：一组线程之间相互等待，直至共同达到某个状态，再继续操作。 可重用。计数值加一。

2. demo：

package com.test.cyclicbarrier;

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

public class CyclicBarrierDemo2 {

    public static void main(String[] args) {
        int threadNum = 10;
        CyclicBarrier barrier = new CyclicBarrier(threadNum, () -> System.out.println("任务完成"));
        for (int i = 0; i < threadNum; i++) {
            new Thread(new Barrier(i, barrier)).start();
        }

    }
}

class Barrier implements Runnable {

    private int num;
    private CyclicBarrier cyclicBarrier;

    public Barrier(int num, CyclicBarrier cyclicBarrier) {
        this.num = num;
        this.cyclicBarrier = cyclicBarrier;
    }

    @Override
    public void run() {
        try {
            TimeUnit.SECONDS.sleep(num);
            System.out.println(Thread.currentThread().getName() + "子程序完成");
            cyclicBarrier.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (BrokenBarrierException e) {
            e.printStackTrace();
        }
    }
}

---

三. 信号量（Semaphore）

用来控制并发数量

应用场景：资源池，对容器施加边界。 

package com.test.semaphore;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.Semaphore;

public class BoundedHashSet<T> {

    private final Semaphore semaphore;
    private final Set<T> set;

    public BoundedHashSet(int bound) {
        this.semaphore = new Semaphore(bound);
        this.set = Collections.synchronizedSet(new HashSet<>());
    }

    public boolean add(T t) {
        boolean wasAdded = false;
        try {
            semaphore.acquire();
            wasAdded = set.add(t);
            return wasAdded;
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            if (!wasAdded)
                semaphore.release();
        }
        return false;
    }

    public boolean remove(Object obj) {
        boolean removed = set.remove(obj);
        if (removed)
            semaphore.release();
        return removed;
    }

}

 

---

package com.test.semaphore;

import java.util.concurrent.Semaphore;

public class SemaphoreDemo extends Semaphore {

    public SemaphoreDemo(int permits, boolean fair) {
        super(permits, fair);
    }

    public static void main(String[] args) {
        Semaphore semaphore = new SemaphoreDemo(3, true);
        for (int i = 0; i < 20; i++) {
            new Thread(() -> {
                try {
                    semaphore.acquire();
                    Thread.sleep(3000);
                    System.out.println(Thread.currentThread().getName() + "任务完成");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    semaphore.release();
                }
            }).start();
        }
    }
}

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四. Exchanger

package com.test.exchanger;

import java.util.concurrent.Exchanger;

public class ExchangerDemo {

    public static void main(String[] args) {
        Exchanger<String> exchanger = new Exchanger<>();
        String str1 = "hello";
        String str2 = "world";
        new Thread(() -> {
            System.out.println(Thread.currentThread().getName() + "===>str1初始值：" + str1);
            try {
                Object obj1 = exchanger.exchange(str1);
                System.out.println(Thread.currentThread().getName() + "===>str1交换值：" + obj1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }).start();
        new Thread(() -> {
            System.out.println(Thread.currentThread().getName() + "===>str2初始值：" + str2);
            try {
                Object obj2 = exchanger.exchange(str2);
                System.out.println(Thread.currentThread().getName() + "===>str2交换值：" + obj2);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }).start();
    }
}