Question

我想模拟一位母亲叫三个孩子吃晚饭，这是我的代码：

class child extends Thread{
    String name;
    mother mom;
    public child(mother mon, String name){
        this.name = name;
        this.mom = mom;
    }

    public void run(){
        System.out.println(name+" is hungry.");
        while (!mom.finished){
            try {
                wait();
            }catch(InterruptedException e){}
        }
        washhands();
    }

    public synchronized void washhands(){
        System.out.println(name+" washed hands.");
        notifyAll();
    }
}

class mother{
    boolean finished;

    public mother(){
        finished = false;
    }
    public void cook(){
        System.out.println("Mom started cooking.");
        try{
            Thread.sleep(200);
        }catch(InterruptedException e){};
        finished = true;
        System.out.println("Mom finished cooking.");
        notifyAll();
    }
}

public class work{
    public static void main(String[] args){
        mother mom = new mother();
        child Alex = new child(mom, "Alex");
        child James = new child(mom, "James");
        child Tod = new child(mom, "Tod");

        Alex.start();
        James.start();
        Tod.start();
        mom.cook();
    }
}

所以我在线程＆＃34; main＆＃34;中得到了一个＆＃34;异常java.lang.IllegalMonitorStateException＆＃34;在班级母亲的notifyAll（）行。我不知道会发生什么，有人可以帮助我吗？

Answer 1

一旦妈妈完成烹饪，你需要通知孩子。现在你在mom对象本身上调用notifyAll（），它看起来功能不正确。一种方法是将子对象引用传递给Mom，并在妈妈完成烹饪后通知他们

Answer 2

考虑以下几点。

您必须使用公共对象来保护所有需要互斥的代码块。
只有当某个对象的监视器被当前线程锁定时才能调用它。
要获取监视器，线程必须进入由拥有监视器的对象保护的块。监视器由JVM内部使用。

除了使用Java naming conventions.

请参阅以下代码

synchronized void method1 () {
}

synchronized void method2() {
}

此处method1和method2将由将要调用它们的对象的监视器守护。因此，如果我们想在一个受保护的区域内使用相同的监视器，它将按如下方式完成。

public void method3() {
    synchronized(this) {
    }
    ...
}

现在method1()，method2()和method3()中的防护块将受到同一个对象监视器的保护。

如果我们需要跨类保护块，那么我们需要在它们之间共享一个共同的对象。我在下面的代码中进行了相同的修改。

package filevisitor;

import java.util.Random;
import java.util.concurrent.atomic.AtomicLong;

class child extends Thread{
    String name;
    volatile mother mom;
    public child(mother mom, String name){
        this.name = name;
        this.mom = mom;
    }

    public void run(){
        System.out.println(name+" is hungry.");
        while (!mom.finished){
            try {
                synchronized(work.myLockObject) {
                    work.myLockObject.wait();
                }
            }catch(InterruptedException e){}
        }
        washhands();
    }

    public void washhands(){
        System.out.println(name+" washed hands.");
        synchronized(work.myLockObject) {
            work.myLockObject.notifyAll();
        }
    }
}

class mother{
    boolean finished;

    public mother(){
        finished = false;
    }
    public void cook(){
        System.out.println("Mom started cooking.");
        try{
            Thread.sleep(200);
        }catch(InterruptedException e){};
        finished = true;
        System.out.println("Mom finished cooking.");
        synchronized(work.myLockObject) {
            work.myLockObject.notifyAll();
        }
    }
}

public class work{
    public static final Object myLockObject = new Object();
    public static void main(String[] args){
        mother mom = new mother();
        child Alex = new child(mom, "Alex");
        child James = new child(mom, "James");
        child Tod = new child(mom, "Tod");

        Alex.start();
        James.start();
        Tod.start();
        mom.cook();
    }
}

儿童班this.mom = mom;还有一个小错误。参数名称为mon，因此此分配无效，导致NullPointerException。

<强>输出

Mom started cooking.
Alex is hungry.
Tod is hungry.
James is hungry.
Mom finished cooking.
Tod washed hands.
James washed hands.
Alex washed hands.

java notifyAll：illegalMonitorStateException

2 个答案: