request_1 and request_2 are just local variable names. The only thing that determines matching order is CC issue order on the communicator. At each process, some CC is issued first and some CC is issued second. The first issued CC at each process will try to match the first issued CC at the other processes. By this rule, rank 0: MPI_Ibcast; MPI_Ibcast Rank 1; MPI_Ibcast; MPI_Ibcast is well defined and
rank 0: MPI_Ibcast; MPI_Ireduce Rank 1; MPI_Ireducet; MPI_Ibcast is incorrect. I do not agree with Jeff on this below. The Proc 1 case where the MPI_Waits are reversed simply requires the MPI implementation to make progress on both MPI_Ibcast operations in the first MPI_Wait. The second MPI_Wait call will simply find that the first MPI_Ibcast is already done. The second MPI_Wait call becomes, effectively, a query function. proc 0: MPI_IBcast(MPI_COMM_WORLD, request_1) // first Bcast MPI_IBcast(MPI_COMM_WORLD, request_2) // second Bcast MPI_Wait(&request_1, ...); MPI_Wait(&request_2, ...); proc 1: MPI_IBcast(MPI_COMM_WORLD, request_2) // first Bcast MPI_IBcast(MPI_COMM_WORLD, request_1) // second Bcast MPI_Wait(&request_1, ...); MPI_Wait(&request_2, ...); That may/will deadlock. Dick Treumann - MPI Team IBM Systems & Technology Group Dept X2ZA / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 From: Jeff Squyres <jsquy...@cisco.com> To: Open MPI Users <us...@open-mpi.org> List-Post: users@lists.open-mpi.org Date: 09/23/2010 10:13 AM Subject: Re: [OMPI users] Question about Asynchronous collectives Sent by: users-boun...@open-mpi.org On Sep 23, 2010, at 10:00 AM, Gabriele Fatigati wrote: > to be sure, if i have one processor who does: > > MPI_IBcast(MPI_COMM_WORLD, request_1) // first Bcast > MPI_IBcast(MPI_COMM_WORLD, request_2) // second Bcast > > it means that i can't have another process who does the follow: > > MPI_IBcast(MPI_COMM_WORLD, request_2) // firt Bcast for another process > MPI_IBcast(MPI_COMM_WORLD, request_1) // second Bcast for another process > > Because first Bcast of second process matches with first Bcast of first process, and it's wrong. If you did a "waitall" on both requests, it would probably work because MPI would just "figure it out". But if you did something like: proc 0: MPI_IBcast(MPI_COMM_WORLD, request_1) // first Bcast MPI_IBcast(MPI_COMM_WORLD, request_2) // second Bcast MPI_Wait(&request_1, ...); MPI_Wait(&request_2, ...); proc 1: MPI_IBcast(MPI_COMM_WORLD, request_2) // first Bcast MPI_IBcast(MPI_COMM_WORLD, request_1) // second Bcast MPI_Wait(&request_1, ...); MPI_Wait(&request_2, ...); That may/will deadlock. -- Jeff Squyres jsquy...@cisco.com For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/ _______________________________________________ users mailing list us...@open-mpi.org http://www.open-mpi.org/mailman/listinfo.cgi/users
