Usage of atomic_thread_fence breaks TSAN

[romasandu-gaijin]

The current state of the art thread sanitizer machinery is not capable of handling thread fences decoupled from atomic operations. And as a multi-threaded system, Jolt surely needs to be testable with TSAN (without getting false-positives due to thread fences being skipped).

Jolt uses atomic_thread_fences in two places, JobSystem.h (Job::Release) and Reference.h (RefTarget::Release). In both places, replacing them with an acq_rel fetch_sub would be (pretty much) semantically equivalent and testable with TSAN, but result in worse codegen on ARM on the hot path (yes, I checked it).

Hence, dirty ifdefs for TSAN builds seem like the only way to go here. I can do a PR if this idea is approved.

[jrouwe]

Hello,

I tried making TSAN work in the (distant) past and couldn't get it to work. If you think you can make it work then yes please make a PR (make sure that it is part of the github build action and runs the unit tests)!

[jrouwe]

B.t.w. I'm hoping this doesn't require lots of changes / annotations?

[romasandu-gaijin]

@jrouwe we are already successfully running autotests that use Jolt w/ TSAN, but after manually trying to run it on a fresh Ubuntu setup I have noticed that GCC complains about thread fences (and rightly so). Alright, I'll do a PR sometime around this week.