JUC并发编程知识点总结

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/**
题目：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-1，
实现交替，来10轮，变量初始值为0.

1. 高内聚低耦合前提下，线程操作资源类

2. 判断/干活/通知

3. 多线程中交互中 必须要，防止多线程的虚假唤醒(判断只能用while，不能用if)

知识小总结：多线程编程套路+while判断+新版写法

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1.高内聚低耦合前提下，线程操作资源类

2.判断/干活/通知

3.多线程交互中，防止虚假唤醒(判断只能用while，不能用if)

4.标志位

一、利用synchronized锁

package com.xiao.test; /**
 * @author zhangxiao
 * @qq 490433117
 * @create_date 2022/6/7 9:27
 */

import com.sun.media.jfxmediaimpl.HostUtils;
import org.junit.Test;

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

/**
 * @author zhangxiao
 * @date 2022/6/7 9:27
 */

// 线程通信   一个线程加1  一个线程减1
public class ThreadWaitNotifyDemo {
    public static void main(String[] args) {
        AirCondtioner airCondtioner = new AirCondtioner();
        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    airCondtioner.increment();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "加1线程A").start();

        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    airCondtioner.increment();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "加1线程B").start();


        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    airCondtioner.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "减1线程C").start();

        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    airCondtioner.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "减1线程D").start();
    }
}

class AirCondtioner {
    private int num = 0;

    // +1
    public synchronized void increment() throws InterruptedException {
        // 判断
        while (num != 0) {
            this.wait();
        }
        // 干活
        num++;
        System.out.println(Thread.currentThread().getName() + "\t" + num);
        // 通知
        this.notifyAll();
    }

    // +1
    public synchronized void decrement() throws InterruptedException {
        // 判断
        while (num == 0) {
            this.wait();
        }
        // 干活
        num--;
        System.out.println(Thread.currentThread().getName() + "\t" + num);
        // 通知
        this.notifyAll();
    }
}

一、利用Lock锁

/**
 * 资源类
 */
class AirCondtioner {
    private int num = 0;
    private Lock lock = new ReentrantLock();
    private Condition condition = lock.newCondition();

    // +1
    public void increment() throws InterruptedException {
        // 判断
        try {
            lock.lock();
            while (num != 0) {
                condition.await();
            }
            // 干活
            num++;
            System.out.println(Thread.currentThread().getName() + "\t" + num);
            // 通知
            condition.signalAll();
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            lock.unlock();
        }

    }

    // +1
    public void decrement() throws InterruptedException {
        // 判断
        try {
            lock.lock();
            while (num == 0) {
                condition.await();
            }
            // 干活
            num--;
            System.out.println(Thread.currentThread().getName() + "\t" + num);
            // 通知
            condition.signalAll();

        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            lock.unlock();
        }

    }
}

多线程之间按顺序调用，实现A->B->C

/**
 * @author zhangxiao
 * @qq 490433117
 * @create_date 2022/6/8 9:57
 */
package com.xiao.test;

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

/**
 * @author zhangxiao
 * @date 2022/6/8 9:57
 */
public class ShareThread {
    public static void main(String[] args) {
        ShareData shareData = new ShareData();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
               shareData.print5();
            }
        },"A").start();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                shareData.print10();
            }
        },"B").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                shareData.print15();
            }
        },"C").start();
    }
}

/**
 * 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
 */
class ShareData {
    private int num = 1;
    private Lock lock = new ReentrantLock();
    private Condition condition1 = lock.newCondition();
    private Condition condition2 = lock.newCondition();
    private Condition condition3 = lock.newCondition();

    public void print5() {
        try {
            lock.lock();
            while (num != 1) {
                condition1.await();
            }

            // 干活
            for (int i = 0; i < 5; i++) {
                System.out.println("print " + i);
            }
            // 通知
            num = 2;
            condition1.signal();
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            lock.unlock();
        }

    }

    public void print10() {
        try {
            lock.lock();
            while (num != 2) {
                condition1.await();
            }

            // 干活
            for (int i = 0; i < 10; i++) {
                System.out.println("print " + i);
            }
            // 通知
            num = 3;
            condition2.signal();
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            lock.unlock();
        }

    }

    public void print15() {
        try {
            lock.lock();
            while (num != 3) {
                condition3.await();
            }

            // 干活
            for (int i = 0; i < 15; i++) {
                System.out.println("print " + i);
            }
            // 通知
            num = 1;
            condition3.signal();
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            lock.unlock();
        }

    }
}

运行结果：

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