线程间通信

线程间通信的模型有两种：共享内存和消息传递

• 以下方式都是基本这两种模 型来实现的。我们来基本一道面试常见的题目来分析 场景—-两个线程，一个线程对当前数值加 1，另一个线程对当前数值减 1,要求 用线程间通信

synchronized方案

public class TestVolatile {
    /**
    * 交替加减
    * @param args
    */
    public static void main(String[] args){
        DemoClass demoClass = new DemoClass();
        new Thread(() ->{
            for (int i = 0; i < 5; i++) {
                demoClass.increment();
            }
        }, "线程 A").start();
        new Thread(() ->{
            for (int i = 0; i < 5; i++) {
                demoClass.decrement();
            }
        }, "线程 B").start();
    }
}
package com.atguigu.test;
class DemoClass{
    //加减对象
    private int number = 0;
    /**
    * 加 1
    */
    public synchronized void increment() {
        try {
            while (number != 0){
                this.wait();
            }
            number++;
            System.out.println("--------" + Thread.currentThread().getName() + "加一成
            功----------,值为:" + number);
            notifyAll();
        }catch (Exception e){
            e.printStackTrace();
        }
    }
    /**
    * 减一
    */
    public synchronized void decrement(){
        try {
            while (number == 0){
                this.wait();
            }
                number--;
                System.out.println("--------" + Thread.currentThread().getName() + "减一成
                功----------,值为:" + number);
                notifyAll();
            }catch (Exception e){
                e.printStackTrace();
        }
    }
}

Lock方案

public class ThreadDemo1 {
    private ReentrantLock reentrantLock = new ReentrantLock();
    private Condition condition = reentrantLock.newCondition();
    private int number = 0;
    private void incr() {
        reentrantLock.lock();
        try {
            while (number != 0) {
                condition.await();
            }
            number++;
            System.err.println("number::" + number);
            condition.signalAll();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            reentrantLock.unlock();
        }
    }
    private void decr() {
        reentrantLock.lock();
        try {
            while (number != 1) {
                condition.await();
            }
            number--;
            System.err.println("number::" + number);
            condition.signalAll();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            reentrantLock.unlock();
        }
    }
    public static void main(String[] args) {
        ThreadDemo1 demo1 = new ThreadDemo1();
        new Thread(()->{
            for (int i = 0; i < 5; i++) {
                demo1.incr();
            }
        },"AA").start();
        new Thread(()->{
            for (int i = 0; i < 5; i++) {
                demo1.incr();
            }
        },"BB").start();
        new Thread(()->{
            for (int i = 0; i < 5; i++) {
                demo1.decr();
            }
        },"CC").start();
        new Thread(()->{
            for (int i = 0; i < 5; i++) {
                demo1.decr();
            }
        },"DD").start();
    }
}