JUC中线程之间得通信

使用synchronized实现线程间通信,线程间通信：1、生产者+消费者2、通知等待唤醒机制.
多线程编程模板:1.判断 2.干活 3.通知

 class ShareDataOne//资源类
{
  private int number = 0;//初始值为零的一个变量
 
  public synchronized void increment() throws InterruptedException 
  {
     //1判断
     if(number !=0 ) {
       this.wait();
     }
     //2干活
     ++number;
     System.out.println(Thread.currentThread().getName()+"\t"+number);
     //3通知
     this.notifyAll();
  }
  
  public synchronized void decrement() throws InterruptedException 
  {
     // 1判断
     if (number == 0) {
       this.wait();
     }
     // 2干活
     --number;
     System.out.println(Thread.currentThread().getName() + "\t" + number);
     // 3通知
     this.notifyAll();
  }
}
/**
 * 
 * @Description:
 *现在两个线程，
 * 可以操作初始值为零的一个变量，
 * 实现一个线程对该变量加1，一个线程对该变量减1，
 * 交替，来10轮。 
 *
 *  * 笔记：Java里面如何进行工程级别的多线程编写
 * 1 多线程变成模板（套路）-----上
 *     1.1  线程    操作    资源类  
 *     1.2  高内聚  低耦合
 * 2 多线程变成模板（套路）-----下
 *     2.1  判断
 *     2.2  干活
 *     2.3  通知
 
 */
public class NotifyWaitDemoOne
{
  public static void main(String[] args)
  {
     ShareDataOne sd = new ShareDataOne();
     new Thread(() -> {
       for (int i = 1; i < 10; i++) {
          try {
            sd.increment();
          } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
          }
       }
     }, "A").start();
     new Thread(() -> {
       for (int i = 1; i < 10; i++) {
          try {
            sd.decrement();
          } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
          }
       }
     }, "B").start();
  }
}

换成4个线程会导致错误，虚假唤醒具体代码可以自己手敲,原因如下:
在java多线程判断时，不能用if，程序出事出在了判断上面，突然有一添加的线程进到if了，突然中断了交出控制权，没有进行验证，而是直接走下去了，加了两次，甚至多次.
所以为了防止虚假唤醒,解决虚假唤醒：查看API，java.lang.Object


image.png

中断和虚假唤醒是可能产生的，所以要用loop循环，if只判断一次 ,while是只要唤醒就要拉回来再判断一次。if换成while
改完之后代码如下

class ShareData//资源类
{
  private int number = 0;//初始值为零的一个变量
 
  public synchronized void increment() throws InterruptedException 
  {
     //判断
     while(number!=0) {
       this.wait();
     }
     //干活
     ++number;
     System.out.println(Thread.currentThread().getName()+" \t "+number);
     //通知
     this.notifyAll();;
  }
  
  public synchronized void decrement() throws InterruptedException 
  {
     //判断
     while(number!=1) {
       this.wait();
     }
     //干活
     --number;
     System.out.println(Thread.currentThread().getName()+" \t "+number);
     //通知
     this.notifyAll();
  }
}
public class NotifyWaitDemo
{
  public static void main(String[] args)
  {
     ShareData sd = new ShareData();
     new Thread(() -> {
 
       for (int i = 1; i <= 10; i++) {
          try {
            sd.increment();
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
       }
     }, "A").start();
     
     new Thread(() -> {
 
       for (int i = 1; i <= 10; i++) {
          try {
            sd.decrement();
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
       }
     }, "B").start();
     new Thread(() -> {
 
       for (int i = 1; i <= 10; i++) {
          try {
            sd.increment();
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
       }
     }, "C").start();
     new Thread(() -> {
 
       for (int i = 1; i <= 10; i++) {
          try {
            sd.decrement();
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
       }
     }, "D").start();
     
  }
}

synchronized和LOCK换代后,wait换成了await,notify换成了 signalAll.


image.png

优化后的代码可以

package com.example.demo.thread;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

class Shradata{
    public int number = 0;

    private Lock lock = new ReentrantLock();
    private Condition condition = lock.newCondition();
    public  void increment() throws Exception {
        lock.lock();
        try {
            while (number != 0 ){
                condition.await();
            }
            number++;
            System.out.println(Thread.currentThread().getName()+"\t"+number);
            condition.signalAll();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }
    public  void decrement() throws Exception {
        lock.lock();
        try {
            while (number == 0 ){
                condition.await();
            }
            number--;
            System.out.println(Thread.currentThread().getName()+"\t"+number);
            condition.signalAll();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }
}

/**
 * @author xie
 * @version 1.0
 * @date 2020/6/27 9:05
 */
public class LockTest {
    public static void main(String[] args) throws Exception{
        Shradata shradata = new Shradata();
        new Thread(()->{
            for (int i = 1;i < 10;i++){
                try {
                    shradata.increment();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        },"A").start();
        new Thread(()->{
            for (int i = 1;i < 10;i++){
                try {
                    shradata.decrement();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        },"B").start();
//        new Thread(()->{
//            for (int i = 1;i < 10;i++){
//                shradata.decrement();
//            }
//        },"C").start();
//        new Thread(()->{
//            for (int i = 1;i < 10;i++){
//                shradata.decrement();
//            }
//        },"D").start();
    }
}

也可以定制化线程间得通信具体
1、有顺序通知，需要有标识位
2、有一个锁Lock，3把钥匙Condition
3、判断标志位
4、输出线程名+第几次+第几轮
5、修改标志位，通知下一个
代码实现:

package com.atguigu.thread;
 
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
 
 
class ShareResource
{
  private int number = 1;//1:A 2:B 3:C 
  private Lock lock = new ReentrantLock();
  private Condition c1 = lock.newCondition();
  private Condition c2 = lock.newCondition();
  private Condition c3 = lock.newCondition();
 
  public void print5(int totalLoopNumber)
  {
     lock.lock();
     try 
     {
       //1 判断
       while(number != 1)
       {
          //A 就要停止
          c1.await();
       }
       //2 干活
       for (int i = 1; i <=5; i++) 
       {
          System.out.println(Thread.currentThread().getName()+"\t"+i+"\t totalLoopNumber: "+totalLoopNumber);
       }
       //3 通知
       number = 2;
       c2.signal();
     } catch (Exception e) {
       e.printStackTrace();
     } finally {
       lock.unlock();
     }
  }
  public void print10(int totalLoopNumber)
  {
     lock.lock();
     try 
     {
       //1 判断
       while(number != 2)
       {
          //A 就要停止
          c2.await();
       }
       //2 干活
       for (int i = 1; i <=10; i++) 
       {
          System.out.println(Thread.currentThread().getName()+"\t"+i+"\t totalLoopNumber: "+totalLoopNumber);
       }
       //3 通知
       number = 3;
       c3.signal();
     } catch (Exception e) {
       e.printStackTrace();
     } finally {
       lock.unlock();
     }
  }  
  
  public void print15(int totalLoopNumber)
  {
     lock.lock();
     try 
     {
       //1 判断
       while(number != 3)
       {
          //A 就要停止
          c3.await();
       }
       //2 干活
       for (int i = 1; i <=15; i++) 
       {
          System.out.println(Thread.currentThread().getName()+"\t"+i+"\t totalLoopNumber: "+totalLoopNumber);
       }
       //3 通知
       number = 1;
       c1.signal();
     } catch (Exception e) {
       e.printStackTrace();
     } finally {
       lock.unlock();
     }
  }  
}
 
 
/**
 * 
 * @Description: 
 * 多线程之间按顺序调用，实现A->B->C
 * 三个线程启动，要求如下：
 * 
 * AA打印5次，BB打印10次，CC打印15次
 * 接着
 * AA打印5次，BB打印10次，CC打印15次
 * ......来10轮  
 *
 */
public class ThreadOrderAccess
{
  public static void main(String[] args)
  {
     ShareResource sr = new ShareResource();
     
     new Thread(() -> {
       for (int i = 1; i <=10; i++) 
       {
          sr.print5(i);
       }
     }, "AA").start();
     new Thread(() -> {
       for (int i = 1; i <=10; i++) 
       {
          sr.print10(i);
       }
     }, "BB").start();
     new Thread(() -> {
       for (int i = 1; i <=10; i++) 
       {
          sr.print15(i);
       }
     }, "CC").start();   
     
     
  }
}

注:若有不足请指正.

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