[Mpi3-hybridpm] Threading homeworking / next telecon

[Barrett, Brian W]

Hi all -

As a reminder, there's a hybrid telecon on Monday, March 25th at 12:00pm
EDT.  During the telcon, we'll be following up from the meeting about
threading (notes below).  Before the meeting, we're supposed to think
about a couple of different issues regarding threads and the MPI spec,
including:

  * which MPI functions have functionality / usability deficiencies if an
MPI does not support MPI_THREAD_MULTIPLE
  * which MPI functions have use cases which present threading issues in
the presence of threads?

Some notes from this week's working group meeting:

  * Jeff H. brought up the fact that library initialization is impossible
to do in a thread safe manner.  Query_thread, for example, may not be
called from the non-main thread in MPI_THREAD_FUNNELED (or by two threads
simultaneously in MPI_THREAD_SERIALIZED).
  * The tools working group has some use cases where the Intialized / Init
race condition is problematic
  * Fab would like us to revive the generalized request discussion; it's a
feature that lacks a significant amount of usability without
MPI_THREAD_MULTIPLE, but MPI_THREAD_MULTIPLE's support is slow in
expanding.
  * Bill brought up the concern that the forum has the tendency to be
two-faced about threads.  We talk about "just use a thread" when trying to
solve a particular problem, then are reluctant to require threads as part
of the model; we should figure out how to deal with that.

Brian

--
  Brian W. Barrett
  Scalable System Software Group
  Sandia National Laboratories