PMIx reigstration callback functions are used when regitering PMIx
event handler.
This patch adjusts two such callback functions:
model_registration_callback()
in ompi/interlib/interlib.c and
ompi_errhandler_registration_callback()
in ompi/errhandler/errhandler.c
Both of them employes the following code structure:
static void xxx_callback(int status,
size_t errhandler_ref,
void *cbdata)
{
myreg_t *trk = (myreg_t*)cbdata;
trk->status = status;
interlibhandler_id = errhandler_ref;
trk->active = false;
}
The workflow is:
1. caller will call opal_pmix.register_evhandler() with
callback function as an argument.
2. caller will call OMPI_LAZY_WAIT_FOR_COMPLETION(trk.active)
to wait for trk->active to became false,
3. PMIx do the registration on anther thread, then call the
registration callback function, which will set trk->active
to false.
4. caller check trk->status to determine whether registration
succeeded.
The expected behavior of the registration callback functions therefore
is that trk->status be updated first, then trk->active be set to false.
However, on ARM based systems, the expected behavior is not guaranteed
because ARM uses a relaxed memory model.
To address this issue, this patch added a call to opal_atomic_wmb()
(write memory barrier) after trk->status being set, to achieve the
expected behavior.
Signed-off-by: Wei Zhang <wzam@amazon.com>
6760d531d5