[Mpi-22] [Mpi-forum] MPI 2.2 proposal: resolving MPI_Request_free issues

[Underwood, Keith D]

> But the MPI standard says this is valid and can be used to avoid the
need 
> to keep track of ISEND request handles. It is clear that if the
matching 
> RECV has completed then the unaltered content of the ISEND buffer is
no 
> longer needed. The RECV cannot have completed unless the message got
out.

I tend to agree with this sentiment, but the MPI standard has long had a
prohibition on touching the transmit buffer, because you never know what
the implementation is using that buffer for.  So... anything that ever
had a reliability protocol and did zero copy has had this issue. 

> Erez is pointing out a case where the semantic stipulated by the MPI 
> standard back before RDMA adapters were available becomes flawed with
the 
> way RDMA adapters now work. The content of the ISEND buffer is
irrelevant 
> once the destination RECV has completed but some other things about
the 
> ISEND buffer are still in limbo

I don't believe this is new.  Anything that ever provided a reason that
you couldn't touch the send buffer likely had a similar issue.

Keith