JUC并发编程 多线程设计模式 -- 同步模式之顺序控制( 固定运行顺序 & 交替输出)

Posted 2021-09-19 Z && Y

1. 固定运行顺序

比如，必须先 2 后 1 打印

---

1.1 示例代码01:

代码:

package tian;

import lombok.extern.slf4j.Slf4j;

@Slf4j(topic = "c.Test25")
public class Test25 {
    static final Object lock = new Object();
    // 表示 t2 是否运行过
    static boolean t2runned = false;

    public static void main(String[] args) {
        Thread t1 = new Thread(() -> {
            synchronized (lock) {
                while (!t2runned) {
                    try {
                        lock.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                log.debug("1");
            }
        }, "t1");


        Thread t2 = new Thread(() -> {
            synchronized (lock) {
                log.debug("2");
                t2runned = true;
                lock.notify();
            }
        }, "t2");

        t1.start();
        t2.start();
    }
}

运行结果:

1.2 示例代码02:

代码:

package tian;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.locks.LockSupport;

@Slf4j(topic = "c.Test26")
public class Test26 {
    public static void main(String[] args) {

        Thread t1 = new Thread(() -> {
            LockSupport.park();
            log.debug("1");
        }, "t1");
        t1.start();

        new Thread(() -> {
            log.debug("2");
            LockSupport.unpark(t1);
        }, "t2").start();
    }
}

运行结果:

---

2. 交替输出

线程 1 输出 a 5 次，线程 2 输出 b 5 次，线程 3 输出 c 5 次。现在要求输出 abcabcabcabcabc 怎么实现

---

2.1 wait notify 版

示例代码:

package tian;

import lombok.extern.slf4j.Slf4j;

@Slf4j(topic = "c.Test27")
public class Test27 {
    public static void main(String[] args) {
        WaitNotify wn = new WaitNotify(1, 5);
        new Thread(() -> {
            wn.print("a", 1, 2);
        }).start();
        new Thread(() -> {
            wn.print("b", 2, 3);
        }).start();
        new Thread(() -> {
            wn.print("c", 3, 1);
        }).start();
    }
}

/*
输出内容       等待标记     下一个标记
   a           1             2
   b           2             3
   c           3             1
 */
class WaitNotify {
    // 打印               a           1             2
    public void print(String str, int waitFlag, int nextFlag) {
        for (int i = 0; i < loopNumber; i++) {
            synchronized (this) {
                while (flag != waitFlag) {
                    try {
                        this.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                System.out.print(str);
                flag = nextFlag;
                this.notifyAll();
            }
        }
    }

    // 等待标记
    private int flag; // 2
    // 循环次数
    private final int loopNumber;

    public WaitNotify(int flag, int loopNumber) {
        this.flag = flag;
        this.loopNumber = loopNumber;
    }
}

运行结果:

---

2.2 ReentrantLock 条件变量版

代码:

package tian;

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

public class Test30 {
    public static void main(String[] args) throws InterruptedException {
        AwaitSignal awaitSignal = new AwaitSignal(5);
        Condition a = awaitSignal.newCondition();
        Condition b = awaitSignal.newCondition();
        Condition c = awaitSignal.newCondition();
        new Thread(() -> {
            awaitSignal.print("a", a, b);
        }).start();
        new Thread(() -> {
            awaitSignal.print("b", b, c);
        }).start();
        new Thread(() -> {
            awaitSignal.print("c", c, a);
        }).start();

        // 睡眠1s先把线程启动
        Thread.sleep(1000);
        awaitSignal.lock();
        System.out.println("开始...");
        a.signal();// 唤醒a上的线程
        awaitSignal.unlock(); // 释放锁
    }
}

class AwaitSignal extends ReentrantLock {
    private int loopNumber;

    public AwaitSignal(int loopNumber) {
        this.loopNumber = loopNumber;
    }

    //            参数1 打印内容， 参数2 进入哪一间休息室, 参数3 下一间休息室
    public void print(String str, Condition current, Condition next) {
        for (int i = 0; i < loopNumber; i++) {
            lock();
            try {
                current.await();
                System.out.print(str);
                next.signal();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                unlock();
            }
        }
    }
}

运行结果:

---

2.3 Park Unpark 版

代码:

package tian;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.locks.LockSupport;

@Slf4j(topic = "c.Test31")
public class Test31 {

    static Thread t1;
    static Thread t2;
    static Thread t3;

    public static void main(String[] args) {
        ParkUnpark pu = new ParkUnpark(5);
        t1 = new Thread(() -> {
            pu.print("a", t2);
        });
        t2 = new Thread(() -> {
            pu.print("b", t3);
        });
        t3 = new Thread(() -> {
            pu.print("c", t1);
        });
        t1.start();
        t2.start();
        t3.start();

        LockSupport.unpark(t1);
    }
}

class ParkUnpark {
    public void print(String str, Thread next) {
        for (int i = 0; i < loopNumber; i++) {
            LockSupport.park();
            System.out.print(str);
            LockSupport.unpark(next);
        }
    }

    private final int loopNumber;

    public ParkUnpark(int loopNumber) {
        this.loopNumber = loopNumber;
    }
}

运行结果:

---

---