Java:线程中的 NotifyObserver 和 DeadLock

Question

我在使用线程时遇到观察者模式和死锁问题。

package observerDeadLock;

import java.util.Observable;

public class MyModel extends Observable {
Integer foo;

public MyModel() {
    foo = 0;
}

public void changeStatus(Integer newStatus) {
    foo = newStatus;
    notifyObservers(newStatus);     
}
}

---

package observerDeadLock;

public class Job extends Thread {
    public MyModel model;

    public Job(MyModel model) {
        super();

        this.model = model;
    }

    public void run() {
        prepareJob();
        runMyJob();
    }

    private void runMyJob() {
        // Some stuff
        Integer choice = 1;

        if (choice == 3) {
            return;
        }
        else if (choice == 2) {
            return;
        }
        else if (choice == 1) {                                     
            model.changeStatus(123);    // Set a particalar status that MyController receive as wrong!
                    // PROBLEM: The Controller listen the changeStatus(123) of notifyObserver of MyModel and call a join() because I want the thread join and quit()
            return; // <<- NEVER EXECUTED! join(timeout) isn't the solution IHMO...s
        }       

        return;
    }

    private void prepareJob() {
        // Do some stuff
    }

package observerDeadLock;

import java.util.Observable;
import java.util.Observer;

public class MyController implements Observer {
    private Job myJob;
    private MyModel model;

    public MyController() {

    }

    public void startJob() {
        model = new MyModel();
        model.addObserver(this);

        myJob = new Job(model);
        myJob.start();
    }

    @Override
    public void update(Observable o, Object arg) {
        if (o instanceof MyModel) {
            if (((Integer) arg) == 1) {     
                // do other stuff
            }
            else if (((Integer) arg) == 2) {        
                // do other stuff
            }
            else if (((Integer) arg) == 123) {      // 123 => Wrong state for myController, so must stop Job
                // Stop myJob!!!
                try {
                    //myJob.join(timeout); // isn' the solution IHMO

                    myJob.join();               // PROBLEM HERE!!! In job, the "return" statment is locked in changeStatus() -> myModel.notifyobserver() that lock here in JOIN();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }           
            }


        }
    }
}

我能做些什么来解决这个问题？我想使用 Thread.join() 而不是 Thread.interrupt() 是一种不好的做法...... 建议？

谢谢!

Answer 1

您显然正在尝试 join() 当前线程(如果将 myJob.join() 替换为 System. out.println( Thread.currentThread() ))，这不是一个好主意，因为线程将永远卡住，或者直到其他人从外部中断它。

不用 join()，只需调用 interrupt()，这没什么可耻的。 (虽然它是否会产生任何影响取决于 runMyJob() 中的其他内容)

更新:我只能假设您为简洁起见编辑了部分代码，但如果 MyController 在遇到退出值 123 时真的什么都不做，而不是停止更新线程，那么整个构造就没有必要了。您应该简单地从 runMyJob() 方法返回而不进行任何设置，线程将正常停止。