This commit adds opal_using_threads() protection around the atomic
operation in OBJ_RETAIN/OBJ_RELEASE. This resolves the performance
issues seen when running psm with MPI_THREAD_SINGLE.
To avoid issues with header dependencies opal_using_threads() has been
moved to a new header (thread_usage.h). The OPAL_THREAD_ADD* and
OPAL_THREAD_CMPSET* macros have also been relocated to this header.
This commit is cherry-picked off a fix that was submitted for the v1.8
release series but never applied to master. This fixes part of the
problem reported by @nysal in #1902.
(cherry picked from commit open-mpi/ompi-release@ce91307918)
Signed-off-by: Nathan Hjelm <hjelmn@me.com>
a8c3699484