[mpi3-coll] Nonblocking collectives standard draft

[Greg Bronevetsky]

>However, if you all already think that MPI_Request_free is bad, then 
>what do you think about the evil MPI_Cancel?

MPI_Cancel is a performance hint as far as I'm concerned, one that is 
frequently ignored. Can you point to any semantic difficulties with it?

Greg Bronevetsky
Post-Doctoral Researcher
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Lawrence Livermore National Lab
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bronevetsky1 at llnl.gov