JUC---05线程间通信（一）

一、普通的线程间通信

　　1.synchronized实现

package com.jenne.mydemo;

class ShareDataOne {

    private int number = 0;

        public synchronized void incr() {
        try {
            //判断
            while (number != 0) {
                wait();
            }
            //干活
            number++;
            System.out.println(Thread.currentThread().getName() + "\t" + number);

            //通知
            notifyAll();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    public synchronized void decr() {
        try {
            //判断
            while (number != 1) {
                wait();
            }
            //干活
            number--;
            System.out.println(Thread.currentThread().getName() + "\t" + number);

            //通知
            notifyAll();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

public class NotifyWaitDemo {

    public static void main(String[] args) {
        ShareDataOne shareDataOne = new ShareDataOne();
        //++
        new Thread(() -> {
            for (int i = 1; i <= 10; i++) {
                shareDataOne.incr();
            }
        }, "AA").start();

        //--
        new Thread(() -> {
            for (int i = 1; i <= 10; i++) {
                shareDataOne.decr();
            }
        }, "BB").start();

        //++
        new Thread(() -> {
            for (int i = 1; i <= 10; i++) {
                shareDataOne.incr();
            }
        }, "CC").start();

        //--
        new Thread(() -> {
            for (int i = 1; i <= 10; i++) {
                shareDataOne.decr();
            }
        }, "DD").start();

    }

}

　　2.Lock锁实现

package com.jenne.mydemo;

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

class ShareDataOne {

    private int number = 0;

    private Lock lock = new ReentrantLock();//创建可重用锁
    private Condition cd = lock.newCondition();//替换Object监测方法（ wait， notify和 notifyAll）等

    public void incr() throws InterruptedException {
        lock.lock();
        try {
            //判断
            while (number != 0) {
                cd.await();
            }
            //干活
            number++;
            System.out.println(Thread.currentThread().getName() + "\t" + number);

            //通知
            cd.signalAll();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }

    }

    public void decr() throws InterruptedException {
        lock.lock();
        try {
            //判断
            while (number != 1) {
                cd.await();
            }
            //干活
            number--;
            System.out.println(Thread.currentThread().getName() + "\t" + number);

            //通知
            cd.signalAll();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
}

public class NotifyWaitDemo {

    public static void main(String[] args) {
        ShareDataOne shareDataOne = new ShareDataOne();

        //++
        new Thread(() -> {
            for (int i = 1; i <= 10; i++) {
                try {
                    shareDataOne.incr();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "AA").start();

        //--
        new Thread(() -> {
            for (int i = 1; i <= 10; i++) {
                try {
                    shareDataOne.decr();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "BB").start();

        //++
        new Thread(() -> {
            for (int i = 1; i <= 10; i++) {
                try {
                    shareDataOne.incr();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "CC").start();

        //--
        new Thread(() -> {
            for (int i = 1; i <= 10; i++) {
                try {
                    shareDataOne.decr();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "DD").start();

    }

}

　　3.注意：

　　　　在上面两种实现简单的线程通信时，判断是否操作都是用while循环。为什么我们不用if判断呢？使用if会造成虚假唤醒操作。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