java - 使用 notifyAll() 的多线程

Question

我正在编写一个 java 程序，打印经过的秒数，每 5 秒打印一条消息。这是一个示例输出:

0 1 2 3 4 hello 5 6 7 8 9 hello 10 11 12 13 14 hello 15 16 17 18 19 hello 

如何删除 boolean 变量 printMsg？有没有更好的线程设计可以做到这一点？

目前，如果没有 printMsg，程序将在 5、10、15 等的 1/10 秒内打印多个“hello”。

class Timer {
    private int count = 0;
    private int N;
    private String msg;
    private boolean printMsg = false;

    public Timer(String s, int N) {
        msg = s;
        this.N = N;
    }

    public synchronized void printMsg() throws InterruptedException{
        while (count % N != 0 || !printMsg)
            wait();
        System.out.print(msg + " ");
        printMsg = false;
    }

    public synchronized void printTime() {
        printMsg = true;
        System.out.print(count + " ");
        count ++;
        notifyAll();
    }

    public static void main(String[] args) {
        Timer t = new Timer("hello", 5);
        new TimerThread(t).start();
        new MsgThread(t).start();
    }
}

class TimerThread extends Thread {
    private Timer t;
    public TimerThread(Timer s) {t = s;}

    public void run() {
        try {
            for(;;) {
                t.printTime();
                sleep(100);
            }
        } catch (InterruptedException e) {
            return;
        }
    }
}

class MsgThread extends Thread {
    private Timer t;
    public MsgThread(Timer s) {t = s;}

    public void run() {
        try {
            for(;;) {
                t.printMsg();
            }
        } catch (InterruptedException e) {
            return;
        }
    }
}

Answer 1

不需要使用 printMsg 标记，当 count % N == 0 时，只需使用 notifyAll 即可

public synchronized void printMsg() throws InterruptedException {
    wait();
    System.out.print(msg + " ");        
}

public synchronized void printTime() {      
    System.out.print(count + " ");
    count++;
    if (count % N == 0){
        notifyAll();    
    }               
}