What‘s the best practices of NSURLSession?

Question

Subscribe my app first:

Most scenes use AFNetworking, a small part of scenes use NSURLSession.sharedSession or create a new NSURLSession.
Using one URLProtocol instance to handle almost all requests, and at the end of -startLoading function, using only one NSURLSession to resume all tasks.

My question is:

I know URLSession instance will cause memory growth and it persists for about 10 minutes, so what is the maximum limit for an app to hold URLSession instances?
What‘s the best practices of NSURLSession？Is it recommended to use only one URLSession instance for the entire app? Or a fixed domain uses a fixed NSURLSession( A-domain using A-session, B-domain using B-session)?
Should I create several URLProtocol instances to handle different domain requests

Thanks!

CouchDeveloper · Answer 1 · 2021-01-12T22:06:58.773

You want to use as few URLSessions as necessary. Usually, this is only one and it's also unlikely you invalidate this session and create a new one during the lifetime of the app.

The reason for having as few as possible, is that URLSession is specifically designed to handle more than one network request - both executing them in parallel or sequential - and can optimise all requests executed in this session in order to use less memory, less power and achieve faster execution times.

On the other hand, there are far less options to optimise requests executed in different URLSessions. Especially performance gains from using HTTP/2 cannot be achieved for requests running in different URLSessions.

However, there may be requirements or situations where you create more than one. For example, you utilise a third party image loading library which creates its own URLSession. Or you need distinct URLSession configurations, like cellular usage, cooky policy or cache policy, etc., which cannot be shared.

Or for example, you want to tie a certain URLSession and it's URLCache and Credential cache to a certain authenticated user. When you have some "sign-out" feature in your app, you can invalidate the session, clear the credential storage and the URLCache. At the same time you have another URLSession for your "public" API, and another URLSession for your image loading, which are not affected by a "sign-out" - and where cached responses should be kept.

It's a gross no-no to create a URLSession for every request, then let this hang around when the request completes and create another URLSession with the next request. You can't do it worse than this.

What‘s the best practices of NSURLSession?

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