App freezes once resume from breakpoint on simulator Xcode9 - deadlock/bug?

Question

Since moving to Xcode 9 I observe a strange behaviour while resuming from a breakpoint on Simulator.

My app uses multiple threads significantly, and some breakpoints are set in the code on different threads. Once the app stops on a breakpoint and then is resumed (repeated a couple of times on different breakpoints) it freezes eventually forever, which looks like a deadlock on a main thread:

• UI is unresponsive (however some UI animations are played) and the callstack shows __ulock_wait on the main thread.

In the same time other background threads shows various actions e.g. on logging mechanism (CocoaLumberjack), downloading pictures (Alamofire), etc. This is not happening while testing on the same breakpoints on a device connected to the Xcode or on previous version of Xcode. I've also tested the behaviour on one of many PODs' demo app used in the app with the same result.

Described behaviour brings debugging experience to annoying level and even breaks possibility to debug some part of the code completely. Could anyone confirm a similar, unwanted behaviour?

Sanmiguel

I have this also with Xcode 9.3 Beta, running on an iPhone X iOS 11.3 Beta. – Crinkle

same here in xcode 9.3 stable version. – Faddish

I confirm, I have encountered this situation, but at real device also. XCode 9.3 – Bloodshot

Additionally, breakpoints set in a synchronized code sometimes didn't fire, but code at this breakpoint evidently has beed executed, in other case rest of the code would lock. – Bloodshot

I have this symptom with Xcode 10.1 on an iPhone X iOS 12.0. – Elegit

@RikRenich is it Xcode problem or CocoaLumberjack ? – Reachmedown

@ParagBafna I am not using CocoaLumberjack. I have no reason to suspect anything other than Xcode. – Elegit