NSUrlSessionHandler allocations can impact performance due to high number of allocations

[Therzok]

Steps to Reproduce

1. DidReceiveResponse
2. DidCompleteWithError
3. DidReceiveResponse again

Here are some sample traces taken while using VSMac and triggering nuget restore on the vsmac solution.

Expected Behavior

⏩

Actual Behavior

[spouliot]

xamarin_get_frame_length is only hit depending on your configuration
Caching it has been tried but did not help (make it worse) as it's not that costly (compared to the caching cost)
There's more details inside #3488

[Therzok]

Yeah, these are the CPU times, but there are still a large number of managed allocations (strings, arrays) coming in from marshalling.

[rolfbjarne]

1. DidReceiveResponse

This should be fixed in #23825.

2. DidCompleteWithError

The Dispose call here happens once per request, so I'm not sure if this is really that much of an issue.

3. DidReceiveResponse again

This doesn't happen when building for Release.