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我是 Java 新手，正在尝试学习活锁的概念。

我在网上找到了一个活锁的好例子，一对夫妻试图喝汤，但他们之间只有一个勺子。夫妻双方都太客气了，对方还没吃饭就递勺子。

我的问题是，我们应该怎么做才能克服一般的活锁问题，在这个特定的例子中？我正在寻找修改我的代码以演示问题的解决方案。

public class Livelock {
    static class Spoon {
        private Diner owner;
        public Spoon(Diner d) { owner = d; }
        public Diner getOwner() { return owner; }
        public synchronized void setOwner(Diner d) { owner = d; }
        public synchronized void use() { 
            System.out.printf("%s has eaten!", owner.name); 
        }
    }

    static class Diner {
        private String name;
        private boolean isHungry;

        public Diner(String n) { name = n; isHungry = true; }       
        public String getName() { return name; }
        public boolean isHungry() { return isHungry; }

        public void eatWith(Spoon spoon, Diner spouse) {
            while (isHungry) {
                // Don't have the spoon, so wait patiently for spouse.
                if (spoon.owner != this) {
                    try { Thread.sleep(1); } 
                    catch(InterruptedException e) { continue; }
                    continue;
                }                       

                // If spouse is hungry, insist upon passing the spoon.
                if (spouse.isHungry()) {                    
                    System.out.printf(
                        "%s: You eat first my darling %s!%n", 
                        name, spouse.getName());
                    spoon.setOwner(spouse);
                    continue;
                }

                // Spouse wasn't hungry, so finally eat
                spoon.use();
                isHungry = false;               
                System.out.printf(
                    "%s: I am stuffed, my darling %s!%n", 
                    name, spouse.getName());                
                spoon.setOwner(spouse);
            }
        }
    }

    public static void main(String[] args) {
        final Diner husband = new Diner("Bob");
        final Diner wife = new Diner("Alice");

        final Spoon s = new Spoon(husband);

        new Thread(new Runnable() { 
            public void run() { husband.eatWith(s, wife); }   
        }).start();

        new Thread(new Runnable() { 
            public void run() { wife.eatWith(s, husband); } 
        }).start();
    }
}
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1 回答 1

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一般来说，活锁没有通用的解决方案。

如果没有检测到任何进展，线程必须停止重复相同的操作。

在您的示例中，允许配偶多次进食（从而检测到所爱的人没有进食并且没有取得任何进展，因为进食只需 1 步）应该迫使勺子的主人只吃。

显然，现实生活中的场景会更加复杂，但检测零进度并采取与平时不同的行动至关重要。

于 2016-02-18T13:07:40.703 回答