带有notifyAll()的多个线程

Question

我正在编写一个打印秒数的java程序,每隔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 

如何删除布尔变量printMsg？是否有更好的线程设计允许这个？

目前,如果没有printMsg,程序将在1/10秒的程序中打印多个"hello",停留在5,10,15等.

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 标志，仅notifyAll当count % N == 0

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();    
    }               
}