从后台线程访问NSManagedObject [英] Accessing NSManagedObject from background thread

问题描述

所以我知道 NSManagedObjects 不是线程安全的，从后台线程获取对象的最好方法是使用 [context objectWithId：id ]; ，因此传递对象ids而不是实际的对象。

So I know NSManagedObjects are not thread safe, and the best way to get objects from a background thread is to use [context objectWithId:id]; , and so pass around object ids instead of the actual object.

假设我有一个全局 NSManagedObject 在我的 AppDelegate （不是最好的设计模式，只是例如） NSManagedObject * myObject;

Let's say I have a global NSManagedObject in my AppDelegate (not the best design pattern, but just for example) NSManagedObject *myObject;

从后台线程访问此对象的 objectId 是否安全？像这样：

Is it safe to access this object's objectId from a background thread? Like this:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
        objectId = appDelegate.myObject.objectId;
        //is this thread safe?
}

推荐答案

这不安全，因为不能保证调用 objectID 在 myObject 访问你的块之外的objectID（例如在主线程上），然后在你的块中使用它：

This is not safe, since there's no guarantee that calling objectID on myObject is safe. You should access the objectID outside of your block (on the main thread, for example) and then use it within your block. Something like:

NSManagedObjectID *objectID = appDelegate.myObject.objectId;
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
    // use objectID here.
}

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