java多线程—常用并发工具类

CountDownLatch

• CountDownLatch

  • 倒计时锁存器

  • CountDownLatch countDownLatch=newCountDownLatch(3);

  • await(),进入等待的状态

  • countDown(),计数器减一

  • 应用场景：启动三个线程计算，需要对结果进行累加。

import java.util.concurrent.CountDownLatch;/**
 * @Author: ruan
 * Date: 2021/7/6 20:42
 * @Description: 倒计时锁存器
 */publicclassTestCountDownLatch{publicstaticvoidmain(String[] args){
        CountDownLatch countDownLatch=newCountDownLatch(3);newThread(()->{try{
                countDownLatch.await();
                System.out.println("计数结束——开始运行");}catch(InterruptedException e){
                e.printStackTrace();}}).start();for(int i=0; i<3; i++){int finalI= i;newThread(()->{int j= finalI;try{
                    Thread.sleep(finalI*1000);
                    System.out.println(Thread.currentThread().getName()+"就绪");}catch(InterruptedException e){
                    e.printStackTrace();}finally{
                    countDownLatch.countDown();}}).start();}}}

CyclicBarrier

• CyclicBarrier
  • 栅栏
  • 允许一组线程相互等待达到一个公共的障碍点，之后再继续执行
  • 跟countDownLatch的区别
    • CountDownLatch一般用于某个线程等待若干个其他线程执行完任务之后，它才执行；不可重复使用
    • CyclicBarrier一般用于一组线程互相等待至某个状态，然后这一组线程再同时执行；可重用的

import java.util.concurrent.BrokenBarrierException;import java.util.concurrent.CyclicBarrier;/**
 * @Author: ruan
 * Date: 2021/7/6 17:38
 * @Description: 多线程之栅栏
 */publicclassTestCyclicBarrier{publicstaticvoidmain(String[] args){
        CyclicBarrier cyclicBarrier=newCyclicBarrier(20,()->{
            System.out.println("人满20 发车");});for(int i=0; i<100; i++){newThread(()->{try{
                    cyclicBarrier.await();}catch(InterruptedException e){
                    e.printStackTrace();}catch(BrokenBarrierException e){
                    e.printStackTrace();}}).start();}}}

ReadWriteLock

• ReadWriteLock
  • 读写锁
    • readLock()读锁可多线程共同读取
    • writeLock()写锁获取锁后其他线程无法操作

import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReadWriteLock;import java.util.concurrent.locks.ReentrantLock;import java.util.concurrent.locks.ReentrantReadWriteLock;/**
 * @Author: ruan
 * Date: 2021/7/6 18:43
 * @Description: 读写锁
 */publicclassTestReadWriteLock{static Lock lock=newReentrantLock();staticint value;static ReadWriteLock readWriteLock=newReentrantReadWriteLock();static Lock readLock= readWriteLock.readLock();static Lock writeLock= readWriteLock.writeLock();publicstaticvoidread(Lock lock){try{
            lock.lock();
            Thread.sleep(1000);
            System.out.println("read over!");}catch(InterruptedException e){
            e.printStackTrace();}finally{
            lock.unlock();}}publicstaticvoidwrite(Lock lock,int v){try{
            lock.lock();
            Thread.sleep(1000);
            value= v;
            System.out.println("write over!");}catch(InterruptedException e){
            e.printStackTrace();}finally{
            lock.unlock();}}publicstaticvoidmain(String[] args){/*for (int i = 0; i < 10; i++) {
            new Thread(()->{
                read(lock);
            }).start();
        }
        for (int i = 0; i < 2; i++) {
            new Thread(()->{
                write(lock,2);
            }).start();
        }*/for(int i=0; i<10; i++){newThread(()->{read(readLock);}).start();}for(int i=0; i<2; i++){newThread(()->{write(writeLock,2);}).start();}}}

Semaphore

• Semaphore

  • 信号量

  • //允许"x"个线程同时进行
    Semaphore semaphore=newSemaphore(x);

  • 控制并发数量

  • 使用场景：接口限流

import java.util.concurrent.Semaphore;/**
 * @Author: ruan
 * Date: 2021/7/6 20:01
 * @Description: 信号量
 */publicclassTestSemaphore{publicstaticvoidmain(String[] args){//允许两个线程同时进行
        Semaphore semaphore=newSemaphore(1);newThread(()->{try{
                semaphore.acquire();
                System.out.println(Thread.currentThread().getName()+"start");
                Thread.sleep(1000);
                System.out.println(Thread.currentThread().getName()+"end");}catch(InterruptedException e){
                e.printStackTrace();}finally{
                semaphore.release();}}).start();newThread(()->{try{
                semaphore.acquire();
                System.out.println(Thread.currentThread().getName()+"start");
                Thread.sleep(1000);
                System.out.println(Thread.currentThread().getName()+"end");}catch(InterruptedException e){
                e.printStackTrace();}finally{
                semaphore.release();}}).start();newThread(()->{try{
                semaphore.acquire();
                System.out.println(Thread.currentThread().getName()+"start");
                Thread.sleep(1000);
                System.out.println(Thread.currentThread().getName()+"end");}catch(InterruptedException e){
                e.printStackTrace();}finally{
                semaphore.release();}}).start();}}

• 信号量为1（只允许一个线程进行）
  
• 信号量为2（允许两个个线程进行）
  

Exchanger

• Exchanger

  • 数据交换
  • 用于交换数据
    • 它提供一个同步点，在这个同步点两个线程可以交换彼此的数据。这两个线程通过exchange方法交换数据， 如果第一个线程先执行exchange方法，它会一直等待第二个线程也执行exchange，当两个线程都到达同步点时，这两个线程就可以交换数据，将本线程生产出来的数据传递给对方。因此使用Exchanger的重点是成对的线程使用exchange()方法，当有一对线程达到了同步点，就会进行交换数据。因此该工具类的线程对象是【成对】的。

import java.util.concurrent.Exchanger;/**
 * @Author: ruan
 * Date: 2021/7/6 20:36
 * @Description: 数据交换
 */publicclassTestExchanger{publicstaticvoidmain(String[] args){
        Exchanger<String> stringExchanger=newExchanger<>();newThread(()->{
            String T1="t1";try{
                String exchange= stringExchanger.exchange(T1);
                System.out.println(Thread.currentThread().getName()+":"+ exchange);}catch(InterruptedException e){
                e.printStackTrace();}},"T1").start();newThread(()->{
            String T2="t2";try{
                String exchange= stringExchanger.exchange(T2);
                System.out.println(Thread.currentThread().getName()+":"+ exchange);}catch(InterruptedException e){
                e.printStackTrace();}},"T2").start();}}