Open Radar

 
Summary:
Normally, when you call -finishTasksAndInvalidate on an NSURLSession, it calls -URLSession:didBecomeInvalidWithError on its delegate as soon as its last task is finished. However, that does not happen with a background session on iOS 10 if the app is sent to background state and back to foreground during download.

Steps to Reproduce:
Open the attached project and Product->Test it on iOS 10 Simulator or device. There is one UI test performing the steps listed below.

Alternatively, you can Run the app and do the same steps manually:
1. Launch the app from the attached project on iOS 10 Simulator or device.
2. Tap "Start Download".
3. Wait for the download to finish.
— The label below will say "Session invalidated", which is expected.
5. Tap "Start Download" again.
6. When the progress indicator starts moving again, press the Home button.
7. Wait 1-2 seconds and tap the app icon again to return to foreground.
8. Wait for the download to finish.
— The label will say "Task completed" but never switch to "Session invalidated".

Expected Results:
-urlSession:didBecomeInvalidWithError: is called and the label shows "Session invalidated".

Actual Results:
-urlSession:didBecomeInvalidWithError: is NOT called and the label shows "Task completed", indicating that only -urlSession:didCompleteWithError: was called.

Version:
iOS 10.0 (14A345), iOS 10.0.1 (14A403)

Notes:
If you call -finishTasksAndInvalidate again after returning to foreground, the session _will_ call -urlSession:didBecomeInvalidWithError: on the delegate after finishing the tasks.

Configuration:
Tried on several iOS devices and simulators, probably any of those

Attachments:
'URLSessionInvalidation.zip' was successfully uploaded. // also available here: https://github.com/glebon/URLSessionInvalidation