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，程序将打印多个＆＃34;你好＆＃34;在1/10秒的节目期间，住在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

简化和更好设计的一个选择是使用单线程而不是两个线程。让单线程处理打印秒和消息。这样可以减少一个线程，不需要wait（）和通知。是否有任何理由要使用两个线程？代码如下：

enter code here
if (e.srcElement.localName == 'textarea') {
  var scrollHeight = e.srcElement.scrollHeight;
  var scrollTop = e.srcElement.scrollTop;
  if (scrollTop >= 0 && screenTop <= scrollHeight) {
       that.dirY = that.dirY * 5;
       e.srcElement.scrollTop = scrollTop + that.dirY;
  }
}

Answer 2

不需要使用printMsg标记，notifyAll时只需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();    
    }               
}

带有notifyAll（）的多个线程

2 个答案: