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iosmultithreadingasynchronousthread-safetynsurlconnection
CodingBeagle
CodingBeagle

Reputation: 1950

Do you need to consider thread-safety using NSURLConnection? - iOS

I've just been wondering for a while now how exactly asynchrounous requests work with NSURLConnection.

For example, suppose you have several upload processes running in your application, all initialized using different instances of NSURLConnection. As uploading processes, your wrapper objects gets the NSURLConnection delegate methods called, like:

-(void)connectionDidFinishLoading:(NSURLConnection*)connection;

Suppose that in all your NSURLConnection wrapper objects share the same delegate object which have a list of all active uploads in an array, and that when the connectionDidFinishLoading gets called for all your connections, they go in and remove themself from that list in the shared delegate object.

The question then is, do you have to worry about thread-safety when those connection objects can access the same array? Or does all those delegate methods go back to the main-thread in such a way that you are not supposed to worry about thread-safety?

Upvotes: 0

Views: 1227

Answers (1)

jackslash
jackslash

Reputation: 8570

The trick is that the delegate methods are called on the thread on which you created your NSURLConnection, which unless you specifically change it will be the main thread. The OS uses one of the threading Queueing APIs to call the delegate method over and over on that thread in the order each connection finishes.

With NSURLConnection its only really the transfer that needs to be threaded. If the transfer happened on the main thread then during the transfer the User wouldn't be able to interact with your iOS application. Doing stuff with the result takes a relatively short time, but if it takes a long time whether you choose to do that processing in the background (on a different thread) or not is then up to you.

Upvotes: 2

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