Java并发编程线程间通讯实现过程详解

package com.zhi.test;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicInteger;

import org.junit.Test;

/**
 * Java多线程-线程通讯示例<br>
 * flag作为共享变量JobB执行，notify通知Job执行，CountDownLatch通知主线程执行
 * 
 * @author 张远志
 * @since 2020年5月4日21:51:24
 *
 */
public class ThreadTest2 {
  private CountDownLatch latch;
  private volatile boolean flag = true;
  private Object lock = new Object();
  private AtomicInteger num = new AtomicInteger(0);

  class JobA implements Runnable {
    @Override
    public void run() {
      synchronized (lock) {
        flag = false;
        if (num.get() != 3) {
          try {
            lock.wait(); // wait方法会释放锁
          } catch (InterruptedException e) {
          }
        }
        System.out.println("任务A收到通知，继续执行作业");
      }
      latch.countDown();
    }
  }

  class JobB implements Runnable {
    @Override
    public void run() {
      while (flag) { // 保证JobA先申请到锁

      }
      synchronized (lock) {
        for (int i = 1; i <= 5; i++) {
          try {
            Thread.sleep(1000);
          } catch (InterruptedException e) {
          }
          int a = num.incrementAndGet();
          System.out.println("任务B第" + i + "次执行，num值为：" + a);
          if (a == 3) {
            lock.notify(); // 唤醒JobB线程，notify方法不会释放锁
          }
        }
      }
      latch.countDown();
    }
  }

  @Test
  public void test() {
    latch = new CountDownLatch(2);
    new Thread(new JobA()).start();
    new Thread(new JobB()).start();
    try {
      latch.await(); // 保证2个线程都执行完毕
    } catch (InterruptedException e) {
    }
  }
}

package com.zhi.test;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.locks.LockSupport;

import org.junit.Test;

/**
 * Java多线程-线程通讯示例，利用LockSupport
 * 
 * @author 张远志
 * @since 2020年5月4日21:51:24
 *
 */
public class ThreadTest3 {
  private CountDownLatch latch;
  private volatile int num = 0;
  private Thread ta;
  private Thread tb;

  class JobA implements Runnable {
    @Override
    public void run() {
      if (num != 3) {
        LockSupport.park();
      }
      System.out.println("任务A收到通知，继续执行作业");
      latch.countDown();
    }
  }

  class JobB implements Runnable {
    @Override
    public void run() {
      for (int i = 1; i <= 5; i++) {
        try {
          Thread.sleep(1000);
        } catch (InterruptedException e) {
        }
        num++;
        System.out.println("任务B第" + i + "次执行，num值为：" + num);
        if (num == 3) {
          LockSupport.unpark(ta); // unpark会立即激活传入线程
        }
      }
      latch.countDown();
    }
  }

  @Test
  public void test() {
    latch = new CountDownLatch(2);
    ta = new Thread(new JobA());
    tb = new Thread(new JobB());
    ta.start();
    tb.start();
    try {
      latch.await(); // 保证2个线程都执行完毕
    } catch (InterruptedException e) {
    }
  }
}