Simultaneous instances of Unity built app leading to Curl errors

Unity Engine
1

I have a Unity project that performs various operations as part of a larger pipeline. I’ve built Windows versions of this application for both DirectX and OpenGL and both applications work really well on various hardware configurations. Part of project makes external REST API requests via UnityWebRequest and uses the data returned. As part of work scaling our pipeline, I am testing running multiple instances of this application (the exe created by Unity) at the same time. When I do, I am seeing many issues during the UnityWebRequest calls, such as:

Curl error 35: Send failure: Connection was reset
(Filename:  Line: 813)

Curl error 35: Handshake failed. UnityTls error code: 7
(Filename:  Line: 813)

Curl error 35: Handshake did not perform verification. UnityTls error code: 7
(Filename:  Line: 813)

Curl error 35: Send failure: Connection was reset
(Filename:  Line: 813)

Curl error 35: Send failure: Connection was aborted
(Filename:  Line: 813)

If I run simultaneous instances from different computers, I am not (yet) able to reproduce the issue.

If there anything about how UnityWebRequest (which apparently uses curl behind the scenes) works that breaks down when multiple instances of the application are running on the same machine?

2

Wow, this smells like smoke leading to a real fire. Can you replicate it in an otherwise empty project that you run twice? Because that would definitely be worth filing a bug.

3

Further digging and it appears that what was happening is that some threads were also running taking most of the CPU cycles at the same time as these web requests were launched. This was leading to the web requests sending data so slowly that the servers receiving the data timed out and closed their connections.