It was noted in Chapter 6, External Interfaces, that
Request Handlers will reappear in a TBD Chapter on Threads.
--I propose that Request Handler semantics be "orthogonal" to Thread semantics. An MPI user should be able to use Request Handlers without having to be concerned with Thread semantics.
A simple suggestion to achieve this "orthogonality": If Threads are present, then the execution of a Request Handler preempts the Thread from which it was posted. A Request Handler could either execute within its posting Thread or block its posting Thread until the Request Handler "returns".
If a MPI User wants a particular Handler or set of Handlers to execute in a separate Thread then the MPI User must first create a Thread and then post the Handler(s) within that Thread.
--This baits a larger discussion regarding MPI-2 and Threads. If an MPI implementation internally creates Threads then should these threads: 1) be transparent to the MPI user and 2) not introduce consistency problems in the presence of an MPI user's Threads.
---------------------------------------------------------------------------- Carter Edwards, carter@ticam.utexas.edu, http://www.ticam.utexas.edu/~carter ----------------------------------------------------------------------------