dispatch_async在NSManagedObjectContext的performBlock [英] dispatch_async in NSManagedObjectContext's performBlock

问题描述

根据WWDC 2012视频核心数据最佳实践， dispatch_sync 应用于在 performBlock 上下文，它是作为 NSPrivateQueueConcurrencyType 类型创建的。

为什么？ / p>

我可以使用 dispatch_async（dispatch_get_main_queue（），0） ...私下调用一些UI相关的回调队列的上下文 performBlock ？

解决方案

NSPrivateQueueConcurrencyType 管理它自己的内部队列，不喜欢你试图离开它的一个线程来做你想做的事情（事实上，我相信它抛出异常，当发生类型的行为）。有几种方法来处理这种情况，当然信号信号是更可接受的设计模式，以获得真正的异步感觉，但正如你所说， dispatch_sync 通常是

According to the WWDC 2012 video, "Core Data Best Practices", dispatch_sync should be used to run some kind of callback in performBlock of context, which is created as a type of NSPrivateQueueConcurrencyType.

Why is that?

Can I use dispatch_async(dispatch_get_main_queue(), 0)... to call some UI-related callbacks in private queue's context's performBlock?

解决方案

No. NSPrivateQueueConcurrencyType manages it's own internal queue, and does not enjoy you trying to leave one of it's threads to do what you want to do (in fact, I believe it throws exceptions when this type of behavior occurs). There's a few ways of handling this, of course signalling semaphores being the more acceptable design pattern to get the truly "async feel", but as you note, dispatch_sync is usually the way to go.

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