To: snir @ watson.ibm.com
cc: mpi-external @ mcs.anl.gov (bcc: Marc Snir/Watson/IBM Research)
Subject: Thread query/init
Marc,
I have two problems with the thread section:
1. I'm sorry, but for me the interface of MPI_THREAD_QUERY/INIT
and "nonstandard mechanism to initialize the thread environment"
looks not very clear.
MPI_THREAD_QUERY( OUT supported,
OUT initialized)
MPI_THREAD_INIT ( IN initialize)
with "supported" returns the "functionality that is supported by
the underlying MPI implementation"
and "initialized" returns the value of used in a previous call to
MPI_THREAD_INIT,
or returns MPI_THREADS_NOT_INITIALIZED
and "initialize" gives the "functionality that the application
wants to use"; the value must be less or equal
the value of "supported"
The infokey "thread_support" is defined along with the values below
(as string) to reduce the supported thread functionality to a
smaller functionality while initiating MPI processes with
mpiexec or MPI_SPAWN.
Functionalities are (increasing order!)
MPI_THREADS_NOT_SUPPORTED
MPI_MPI_CALLS_ONLY_FROM_MAIN_THREAD
MPI_MPI_CALLS_ONLY_FROM_ONE_THREAD
MPI_MPI_NOT_CALLED_FROM_PARALLEL_THREADS
MPI_MULTIPLE_THREADS
****
I have no problem with this variant, provided that the keywords get shorter
(31 max!)
*****
2. How do we handle the malloc-problem? (On the next mail)
****
We already have similar problems with signals, and we ask that the
implementation refrain from using,
if possible, some signals, and document what signals are used.
An MPI implementation should document which C lib calls it is making that
are not thread safe, and what mutex can be used to protect such call.
Beyond that, we can ask that an MPI implementation does not make certain C
lib
calls, if those are not thread safe, so as not to conflict with such calls
made by user code.
I have no problem with mandating that an MPI library does not invoke
malloc,
if malloc is not thread-safe.
Has anybody gone systematically thru a Posix standard doc, to figure out
what is guaranteed to be thread dafe, and what is not?
Marc
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