Hi all,
I'm trying to debug a problem with a custom scheduler
(https://xgitlab.cels.anl.gov/sds/abt-snoozer/issues/8) To make a long
story short, sometimes we can trigger a scenario where unlocking a mutex
does not wake up any ULTs that are blocked on it.
I've traced something suspicious in ABTI_mutex_wake_de() path leading up
to the deadlock, but I'm not sure if this is an Argobots bug or if I
just don't understand the logic. Can someone help sanity check this?
In the ABTI_mutex_wake_de() invocation just before the hang, the value
of num_elem is 1 at this line:
https://github.com/pmodels/argobots/blob/master/src/mutex.c#L769
... but then after checking the high and low priority lists it falls
through to here, having not found anything to wake up:
https://github.com/pmodels/argobots/blob/master/src/mutex.c#L802
Is that code path supposed to be possible?
It seems non intuitive that the count could be > 0 but it can't find a
thread to wake up, but there might be a more subtle meaning to
num_elem. The particular scheduler that I am debugging will be
blocking/sleeping until it finds work to do, so it's important that this
path ultimately triggers a pool push or else it won't make progress.
That may not be an issue with other schedulers.
thanks!
-Phil
