in the v1.2 series the cid's could never go above the max. allowed for a
particular pml. Because of that, pml_add_comm never checked for the cid, and
in fact pml_add_comm was called in comm_set, which is *before* we knew the
cid.
in the v1.3 series (and trunk) we check now the cid to detect overflow, and
because of that pml_add_comm has been moved *after* the cid allocation
routine, namely into the comm_activate routine.
in the v1.2 series, the comm_activate contained a synchronization step of the
old communicator in order to prevent incoming fragments on the new
communicator, with the main problem being that the allreduce in the
communicator allocation finished at different times on different processes,
and thus, this scenario could and did really occur.
in the v1.3 series, the comm_activate does not contain the synchronization
step anymore, since we introduced the new queue for fragments with unknown
cid. The problem is however, that whether a fragment is known or not is
decided by using ompi_comm_lookup(), which will return something useful as
soon as the cid allocation finished, even before pml_add_comm has been
called. So there is a small time gap where we will not post a message into
queue for unknown cid's, but we can also not look up the process structure
belonging to the rank in that comm ( that is in pml_ob1_match_recv_frag or
something like that).
The current fix reintroduces the synchronization step in comm_activate, and
ensures that no fragment can be received for a new communicator before the
synchronization occurs , and thus comm_nextcid() and pml_add_comm has been
called. It seems to be the safest and easiest way for now. Welcome back, v1.2.
This commit was SVN r21970.
9abeaad6e2