您如何在不忙于等待的情况下暂停线程直到条件变为真? [英] How do you pause a thread until a condition becomes true without busy waiting?

问题描述

如何在不忙等待的情况下暂停线程直到条件变为真? 例如，假设我正在检查

How do you pause a thread until a condition becomes true without busy waiting? For example, suppose I'm checking to see whether

playerOne.isWalking()

playerOne.isWalking()

这将是真实的，并且当它变为真实时，我想运行一些代码.再次假设playerOne是Player类的实例，然后该类具有isWalking()函数.我无法访问使isWalking()变为true的内容.因此，每次我要检查isWalking()是否为true时，都必须从player实例中显式调用该方法.

Is going to be true and I want to run some code when it does become true. Again suppose playerOne is an instance of the class Player which then has the function isWalking(). I do not have access to the what makes isWalking() become true. So everytime I want to check to see if isWalking() is true, I have to call the method from an instance of player explicitly.

我已经尝试在同步块中使用Wait/Notify，但这将永远无法正常工作，因为当isWalking()变为true且我不知道何时将变为true时，我必须手动通知线程唤醒

I've tried using Wait/Notify in synchronized blocks but that wouldn't ever work because I would have to manually notify the Thread to wake up when isWalking() becomes true and I don't know when it will become true.

我尝试使用观察者模式使Player成为可观察的子类，以便在isWalking()变为true时可以调用update方法，但是我也不知道何时会发生.

I've tried using the observer pattern to make Player a subclass of observable so that I can call the update method when isWalking() becomes true but again I don't know when that will happen.

我什至尝试使用属性，但这也不起作用.

I've even tried using Propertys but that wouldn't work either.

甚至无需等待就可以检查吗?不断轮询并调用该函数以查看其是否为真，然后，如果它为真，则执行代码.

Is this even possible to check without busy-waiting? Constantly polling and calling that function to see if it is true, then if it is true, execute the code.

这是我在忙碌等待中做出的糟糕解决方案:

This was a bad solution I made involving busy-waiting:

忙等待解决方案

推荐答案

潜在的问题是您使用 getter 方法获取信息并对其进行操作.此处违反的原则是告诉，不要问！.

The underlaying problem is that you use a getter method to aquire an information and act on it. The principle which is violated here is Tell, don't ask!.

OO解决此问题的方法是引入接口(例如:PlayerMovingListener).

The OO whay to solve this is to introduce an interface (e.g.: PlayerMovingListener).

player类将包含实现该接口的对象的实例(或它们的列表).播放器一开始走动，就会调用由播放器所拥有的(或所有)侦听器对象实现的接口中定义的isMoving()方法.
^{很可能是由当前Payer实现中的setter方法触发的.}

The player class would hold an instance of an object implementing that interface (or a list of them). As soon as the player starts walking it calls the isMoving() method defined in the interface implemented by the (or all) listener object(s) held by the player.
^{Most likely is triggered by a setter method in your current Payer implementation.}

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