That means the MPI implementation would need to make a copy of potentially large lists. Reference counting won't work here. And the user could easily issue several nonblocking calls in a row. Ouch. Rajeev _____ From: [email protected] [mailto:[email protected]] On Behalf Of Graham, Richard L. Sent: Saturday, August 01, 2009 9:57 AM To: '[email protected]' Subject: Re: [mpi3-coll] array parameters in nonblocking collectives I would expect that the user arguments shouild not be expected to be preserved in the user's arrays between posting the collectives and completing them. Rich _____ From: [email protected] To: Torsten Hoefler Cc: MPI-3 Collective Subgroup Discussions Sent: Sat Aug 01 09:56:50 2009 Subject: [mpi3-coll] array parameters in nonblocking collectives Hi, I have one question about the array parameters (sendcounts, recvcounts, sdispls and rdispls) in nonblocking collectives such as MPI_IALLTOALLV. Are callers allowed to modify/destroy those arrays upon the return of the calls, or they must wait until after the MPI_WAIT call? I could not find the correct behavior defined in the latest proposal (nbc-proposal-rev-6.2.pdf) and do not remember having discussion on such. I think this issue is quite unique to nonblocking collective communication calls since arrays in other MPI nonblocking calls are arrays of MPI objects, for which the correct handling is well defined. So it needs to be clarified. Am I missing something? Thanks Bin Jia Communication Protocol Development Advanced Clustering Technology Team, IBM STG Poughkeepsie, NY 12601 Tel: 845-433-6301(T/L 293-)