`LockTrace::enter` causes terrible performance on debug (creates many backtraces)

[vxpm]

apparently, LockTrace's enter method creates a backtrace every time it's called - which is terrible performance wise:

this only happens on debug, but the performance hit is too high to be acceptable (in my opinion). maybe gating the backtrace behind a feature would make sense, given it is a feature to help debug code that tries to acquire the lock recursively?

[jimblandy]

LockTrace::enter calls Backtrace::capture, so it should only be capturing backtraces when you've got environment variables set. Is that not the case?

[vxpm]

yes it is - however, i'm not debugging wgpu, i'm debugging something else entirely. it still doesn't make sense to keep capturing so many backtraces.

[jimblandy]

We'd take a PR to check a WGPU_SNATCHLOCK_BACKTRACE environment variable that enables capturing backtraces if its value is 1. Probably a static holding a LazyLock<bool> would work.