在序列 java 中运行 3 个线程

multithreading java notify

2022-09-03 13:44:25

我有3个线程第一次打印 A 第二次打印 B 第三次打印 C

我想按顺序打印 A B C A B C A B C 等等.....

所以我写了下面的程序，但我无法实现同样的目标。我意识到一个问题，当状态=1时，例如B1和C1线程正在等待，当我通知All（）时，等待线程都会唤醒，并且根据CPU分配，它可能会打印B或C。

在这种情况下，我只想在A之后打印B。

我需要做什么修改。

public class NotifyAllExample {

    int status=1;
    public static void main(String[] args) {

        NotifyAllExample notifyAllExample = new NotifyAllExample();

        A1 a=new A1(notifyAllExample);
        B1 b=new B1(notifyAllExample);
        C1 c=new C1(notifyAllExample);

        a.start();
        b.start();
        c.start();
    }
}

class A1 extends Thread{
    NotifyAllExample notifyAllExample;

    A1(NotifyAllExample notifyAllExample){
        this.notifyAllExample = notifyAllExample;
    }

    @Override
    public void run() {

        try{
            synchronized (notifyAllExample) {

                for (int i = 0; i < 100; i++) {

                    if(notifyAllExample.status!=1){
                        notifyAllExample.wait();
                    }

                    System.out.print("A ");
                    notifyAllExample.status = 2;
                    notifyAllExample.notifyAll();
                }

            }
        }catch (Exception e) {
            System.out.println("Exception 1 :"+e.getMessage());
        }

    }

}

class B1 extends Thread{

    NotifyAllExample notifyAllExample;

    B1(NotifyAllExample notifyAllExample){
        this.notifyAllExample = notifyAllExample;
    }

    @Override
    public void run() {

        try{
            synchronized (notifyAllExample) {

                for (int i = 0; i < 100; i++) {

                    if(notifyAllExample.status!=2){
                        notifyAllExample.wait();
                    }

                    System.out.print("B ");
                    notifyAllExample.status = 3;
                    notifyAllExample.notifyAll();
                }

            }
        }catch (Exception e) {
            System.out.println("Exception 2 :"+e.getMessage());
        }

    }
}


class C1 extends Thread{

    NotifyAllExample notifyAllExample;

    C1(NotifyAllExample notifyAllExample){
        this.notifyAllExample = notifyAllExample;
    }

    @Override
    public void run() {

        try{
            synchronized (notifyAllExample) {

                for (int i = 0; i < 100; i++) {

                    if(notifyAllExample.status!=3){
                        notifyAllExample.wait();
                    }

                    System.out.print("C ");
                    notifyAllExample.status = 1;
                    notifyAllExample.notifyAll();
                }

            }
        }catch (Exception e) {
            System.out.println("Exception 3 :"+e.getMessage());
        }

    }
}

答案 1

将这些 IF 语句转换为 WHILE 语句以获得所需的行为：

if (notifyAllExample.status != 2){
    notifyAllExample.wait();
}

自

while (notifyAllExample.status != 2){
    notifyAllExample.wait();
}

这将确保如果线程收到通知，在状态值达到预期值之前，它不会退出 while 循环。

此外，请标记为易失性，以便线程不会有本地副本。status

答案 2

 public class RunThreadsInOrder implements Runnable {

    static int numThread = 1;
    static int threadAllowedToRun = 1;
    int myThreadID;
    private static Object myLock = new Object();

    public RunThreadsInOrder() {
        this.myThreadID = numThread++;
        System.out.println("Thread ID:" + myThreadID);
    }

    @Override
    public void run() {
        synchronized (myLock) {
            while (myThreadID != threadAllowedToRun) {
                try {
                    myLock.wait();
                } catch (InterruptedException e) {

                } catch (Exception e) {}
            }
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
            }

            System.out.println("myThreadID is running: " + myThreadID);
            myLock.notifyAll();
            threadAllowedToRun++;
        }
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Thread t1 = new Thread(new RunThreadsInOrder());
        Thread t2 = new Thread(new RunThreadsInOrder());
        Thread t3 = new Thread(new RunThreadsInOrder());
        Thread t4 = new Thread(new RunThreadsInOrder());
        Thread t5 = new Thread(new RunThreadsInOrder());
        Thread t6 = new Thread(new RunThreadsInOrder());
        Thread t7 = new Thread(new RunThreadsInOrder());

        t7.start();
        t6.start();
        t5.start();
        t4.start();
        t3.start();
        t2.start();
        t1.start();

    }
}