FastGeo Job Queue Race Condition

Development Platform & Builds
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1

I suspect that when FFastGeoAsyncRenderStateJobQueue::Tick happens if there is queued work started by FFastGeoAsyncRenderStateJobQueue::Launch that FFastGeoAsyncRenderStateJobQueue::AreAsyncTasksExecuted could return true because UE::Tasks::HasWork loads the TaskCount atomic with std::memory_order_relaxed. When FFastGeoAsyncRenderStateJobQueue::AreAsyncTasksExecuted is then true but work is still in flight the check(PipeTasks.IsEmpty()); fails.

2

Steps to Reproduce
Load into a very content dense scene and then teleport to another part of the world that is also very content dense and sometimes a check trips.

3

Hi Bryan, you are right, the checks are invalid.

I will go ahead and remove that whole chunk of code :

#if DO_CHECK
	if (AreAsyncTasksExecuted())
	{
		check(PipeTasks.IsEmpty());
		check(PipedJobs.IsEmpty());
		check(!IsReadyToRunAsyncTasksEvent.IsSet());
	}
#endif
4

Submitted fix in our main branch (CL 46886071).

Thanks

5

I have also confirmed that added update to the FFastGeoAsyncRenderStateJobQueue class using bForceWaitCompletion to WaitForAsyncTasksExecution does not resolve the issue as the path taken to Tick seen has bForceWaitCompletion false.