FirebaseDatabase Thread Performance Checker warning

[Serg-Pogrebnyak]

FirebaseDatabase Thread Performance Checker warning

[google-oss-bot]

I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.

[Serg-Pogrebnyak]

I've built a minimal reproducing build, you can find it in my GitHub.
MacOS 14.4.1
XCode 15.3
iOS 17.4.1 (iPhone 12 mini, iPhone 12 Pro)

The first few launches should be okay, but after 3-4, you should catch this warning.

[paulb777]

Successfully reproduced on the first run on an iPhone 13

[paulb777]

Thanks for the report and repro @Serg-Pogrebnyak. Before we try the repro, would you check #10130 and https://stackoverflow.com/q/72533064/556617 to see if anything in those conversations helps your example.

[Serg-Pogrebnyak]

Thanks for your reply! 
Checked and nothing helps. I've put the firebase initialization in the DispatchQueue.global.async code block, I do not have DispatchGroup in my code base at all, and checked qualityOfService it installed as NSQualityOfServiceUserInitiated. Looks like it's something new

[paulb777]

Thanks. Does is repro on the simulator or only on devices?

[Serg-Pogrebnyak]

I've developed on the simulator and never saw this issue (MacBook Pro M1 Pro, 16/512), but on the real device, I received this warning. Will be fine if you check on the real device with the same iOS version I guess.

[morganchen12]

The thread that's being blamed for this is possibly the FIRDatabaseQuery worker queue. But there's no waiting happening in the RTDB code itself, and the stack trace seems to point toward something deep in CFNetwork for the actual thread blocking that's causing the priority inversion. Searching for the blamed symbol, estimatedPropertyListSize, suggests this might be an Apple bug: https://forums.developer.apple.com/forums/thread/747859

[paulb777]

@Serg-Pogrebnyak #12894 fixes the repro case and passes our tests. Would you confirm it works for your app?

[Serg-Pogrebnyak]

@paulb777 yes, now all fine! Thank you so much!
I've checked on the test and real projects and both look fine now🎉
Thanks again!🙏🏻