[Mpi3-hybridpm] Threading homeworking / next telecon

Jeff Hammond jhammond at alcf.anl.gov
Mon Mar 25 11:18:13 CDT 2013

In case people aren't on the call or didn't hear me clearly,
https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/371 is related to
the two-faced issue of threads.



On Thu, Mar 14, 2013 at 4:45 PM, Rajeev Thakur <thakur at mcs.anl.gov> wrote:
> The analysis of thread safety needs of MPI routines that Bill mentioned on Wed is available here: http://wiki.mpich.org/mpich/index.php/Thread_Safety . It is referenced in this paper, www.mcs.anl.gov/~thakur/papers/threads-parco.pdf.
> Rajeev
> On Mar 14, 2013, at 3:00 PM, Barrett, Brian W wrote:
>> 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
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Jeff Hammond
Argonne Leadership Computing Facility
University of Chicago Computation Institute
jhammond at alcf.anl.gov / (630) 252-5381

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