Question

我想分别使用wait（）/ notify（）应用暂停/恢复线程。我已反复尝试解决此问题，但无法解决，因此请帮助我并解释为什么notify（）;。不能使计数器线程可运行：

public class Suspend {
boolean isSuspend = false;
int counter = 0;

synchronized public void suspend() {    
    isSuspend = true;
    System.out.println("The counter was suspended!");
}

synchronized public void resume() {
    isSuspend = false;
    System.out.println("The counter was resumed :)");
    notify();
}

public static void main(String[] args) {
    Thread.currentThread().setName("Main Thread");
    Suspend suspend = new Suspend();

    Thread counterThread = new Thread(new Runnable() {
        synchronized public void run() {
            while(!suspend.isSuspend) {
                System.out.println(suspend.counter++);
                try { Thread.sleep(1000); }
                catch (InterruptedException e) {}
            }
            try {
                while(suspend.isSuspend)
                    wait();
                }
            catch (InterruptedException e) {}
        }
    }, "Counter Thread");

    Thread suspendResumeThread = new Thread(new Runnable() {
        synchronized public void run() {
            while(true) {
                try {
                    Thread.sleep(5000);
                    suspend.suspend();
                    Thread.sleep(5000);
                    suspend.resume();
                } catch (InterruptedException e) {}
            }
        }
    }, "Suspend/Resume Thread");

    counterThread.start();
    suspendResumeThread.start();
}

}

输出如下： 0 1 2 3 4 The counter was suspended! The counter was resumed :) The counter was suspended! The counter was resumed :) ... and so on.

Answer 1

问题在于这些行：

while (suspend.isSuspend)
    wait();
}

在您的counterThread可运行文件中。

您等待Runnable，而不是suspend对象

您需要在suspend上进行同步，并在suspend上调用wait（）：

synchronized (suspend) {
    while (suspend.isSuspend)
        suspend.wait();
    }
}

此外，您的run方法不需要同步。

Answer 2

看看counterThread，它在isSuspend标志的第一次更改时结束。

我认为您需要这样的东西：

public class Suspend {
volatile boolean isSuspend = false;
int counter = 0;

synchronized public void suspend() {    
    isSuspend = true;
    System.out.println("The counter was suspended!");
}

synchronized public void resume() {
    isSuspend = false;
    System.out.println("The counter was resumed :)");
    notify();
}

public static void main(String[] args) {
    Thread.currentThread().setName("Main Thread");
    Suspend suspend = new Suspend();

    Thread counterThread = new Thread(new Runnable() {
        synchronized public void run() {
            while(true){
                while(!suspend.isSuspend) {
                    System.out.println(suspend.counter++);
                    try { Thread.sleep(1000); }
                    catch (InterruptedException e) {}
                }
                try {
                    while(suspend.isSuspend)
                        wait();
                }catch (InterruptedException e) {}
                }
             }
         }
    }, "Counter Thread");

    Thread suspendResumeThread = new Thread(new Runnable() {
        synchronized public void run() {
            while(true) {
                try {
                    Thread.sleep(5000);
                    suspend.suspend();
                    Thread.sleep(5000);
                    suspend.resume();
                } catch (InterruptedException e) {}
            }
        }
    }, "Suspend/Resume Thread");

    counterThread.start();
    suspendResumeThread.start();
}

最后，您还需要在共享变量上使用volatile关键字

编辑：抱歉，我粘贴了错误的代码

Java中的暂停和恢复线程不起作用

2 个答案: