Hi, Thanks for the reply. But this can not solve the problem.
The output indicate that both nodes hang at the second MPI_Wait, and no one can reaches the MPI_Finalize. >> >> *********************************************** >> >> Hello from processor 0 of 2 >> >> >> >> Received one message >> >> >> >> Hello from processor 1 of 2 >> >> >> >> Sent one message >> >> ******************************************************* Any other thoughts or suggestions? Thanks! Kong On Tue, Feb 22, 2011 at 11:06 AM, Bill Rankin <bill.ran...@sas.com> wrote: > Try putting an "MPI_Barrier()" call before your MPI_Finalize() [*]. I > suspect that one of the programs (the sending side) is calling Finalize > before the receiving side has processed the messages. > > -bill > > [*] pet peeve of mine : this should almost always be standard practice. > > >> -----Original Message----- >> From: users-boun...@open-mpi.org [mailto:users-boun...@open-mpi.org] On >> Behalf Of Xianglong Kong >> Sent: Tuesday, February 22, 2011 10:27 AM >> To: Open MPI Users >> Subject: Re: [OMPI users] Beginner's question: why multiple sends or >> receives don't work? >> >> Hi, Thank you for the reply. >> >> However, using MPI_waitall instead of MPI_wait didn't solve the >> problem. The code would hang at the MPI_waitall. Also, I'm not quit >> understand why the code is inherently unsafe. Can the non-blocking >> send or receive cause any deadlock? >> >> Thanks! >> >> Kong >> >> On Mon, Feb 21, 2011 at 2:32 PM, Jeff Squyres <jsquy...@cisco.com> >> wrote: >> > It's because you're waiting on the receive request to complete before >> the send request. This likely works locally because the message >> transfer is through shared memory and is fast, but it's still an >> inherently unsafe way to block waiting for completion (i.e., the >> receive might not complete if the send does not complete). >> > >> > What you probably want to do is build an array of 2 requests and then >> issue a single MPI_Waitall() on both of them. This will allow MPI to >> progress both requests simultaneously. >> > >> > >> > On Feb 18, 2011, at 11:58 AM, Xianglong Kong wrote: >> > >> >> Hi, all, >> >> >> >> I'm an mpi newbie. I'm trying to connect two desktops in my office >> >> with each other using a crossing cable and implement a parallel code >> >> on them using MPI. >> >> >> >> Now, the two nodes can ssh to each other without password, and can >> >> successfully run the MPI "Hello world" code. However, when I tried >> to >> >> use multiple MPI non-blocking sends or receives, the job would hang. >> >> The problem only showed up if the two processes are launched in the >> >> different nodes, the code can run successfully if the two processes >> >> are launched in the same node. Also, the code can run successfully >> if >> >> there are only one send or/and one receive in each process. >> >> >> >> Here is the code that can run successfully: >> >> >> >> #include <stdlib.h> >> >> #include <stdio.h> >> >> #include <string.h> >> >> #include <mpi.h> >> >> >> >> int main(int argc, char** argv) { >> >> >> >> int myrank, nprocs; >> >> >> >> MPI_Init(&argc, &argv); >> >> MPI_Comm_size(MPI_COMM_WORLD, &nprocs); >> >> MPI_Comm_rank(MPI_COMM_WORLD, &myrank); >> >> >> >> printf("Hello from processor %d of %d\n", myrank, nprocs); >> >> >> >> MPI_Request reqs1, reqs2; >> >> MPI_Status stats1, stats2; >> >> >> >> int tag1=10; >> >> int tag2=11; >> >> >> >> int buf; >> >> int mesg; >> >> int source=1-myrank; >> >> int dest=1-myrank; >> >> >> >> if(myrank==0) >> >> { >> >> mesg=1; >> >> >> >> MPI_Irecv(&buf, 1, MPI_INT, source, tag1, >> MPI_COMM_WORLD, &reqs1); >> >> MPI_Isend(&mesg, 1, MPI_INT, dest, tag2, >> MPI_COMM_WORLD, &reqs2); >> >> >> >> >> >> } >> >> >> >> if(myrank==1) >> >> { >> >> mesg=2; >> >> >> >> MPI_Irecv(&buf, 1, MPI_INT, source, tag2, >> MPI_COMM_WORLD, &reqs1); >> >> MPI_Isend(&mesg, 1, MPI_INT, dest, tag1, >> MPI_COMM_WORLD, &reqs2); >> >> } >> >> >> >> MPI_Wait(&reqs1, &stats1); >> >> printf("myrank=%d,received the message\n",myrank); >> >> >> >> MPI_Wait(&reqs2, &stats2); >> >> printf("myrank=%d,sent the messages\n",myrank); >> >> >> >> printf("myrank=%d, buf=%d\n",myrank, buf); >> >> >> >> MPI_Finalize(); >> >> return 0; >> >> } >> >> >> >> And here is the code that will hang >> >> >> >> #include <stdlib.h> >> >> #include <stdio.h> >> >> #include <string.h> >> >> #include <mpi.h> >> >> >> >> int main(int argc, char** argv) { >> >> >> >> int myrank, nprocs; >> >> >> >> MPI_Init(&argc, &argv); >> >> MPI_Comm_size(MPI_COMM_WORLD, &nprocs); >> >> MPI_Comm_rank(MPI_COMM_WORLD, &myrank); >> >> >> >> printf("Hello from processor %d of %d\n", myrank, nprocs); >> >> >> >> MPI_Request reqs1, reqs2; >> >> MPI_Status stats1, stats2; >> >> >> >> int tag1=10; >> >> int tag2=11; >> >> >> >> int source=1-myrank; >> >> int dest=1-myrank; >> >> >> >> if(myrank==0) >> >> { >> >> int buf1, buf2; >> >> >> >> MPI_Irecv(&buf1, 1, MPI_INT, source, tag1, >> MPI_COMM_WORLD, &reqs1); >> >> MPI_Irecv(&buf2, 1, MPI_INT, source, tag2, >> MPI_COMM_WORLD, &reqs2); >> >> >> >> MPI_Wait(&reqs1, &stats1); >> >> printf("received one message\n"); >> >> >> >> MPI_Wait(&reqs2, &stats2); >> >> printf("received two messages\n"); >> >> >> >> printf("myrank=%d, buf1=%d, buf2=%d\n",myrank, buf1, >> buf2); >> >> } >> >> >> >> if(myrank==1) >> >> { >> >> int mesg1=1; >> >> int mesg2=2; >> >> >> >> MPI_Isend(&mesg1, 1, MPI_INT, dest, tag1, >> MPI_COMM_WORLD, &reqs1); >> >> MPI_Isend(&mesg2, 1, MPI_INT, dest, tag2, >> MPI_COMM_WORLD, &reqs2); >> >> >> >> MPI_Wait(&reqs1, &stats1); >> >> printf("sent one message\n"); >> >> >> >> MPI_Wait(&reqs2, &stats2); >> >> printf("sent two messages\n"); >> >> } >> >> >> >> MPI_Finalize(); >> >> return 0; >> >> } >> >> >> >> And the output of the second failed code: >> >> *********************************************** >> >> Hello from processor 0 of 2 >> >> >> >> Received one message >> >> >> >> Hello from processor 1 of 2 >> >> >> >> Sent one message >> >> ******************************************************* >> >> >> >> Can anyone help to point out why the second code didn't work? >> >> >> >> Thanks! >> >> >> >> Kong >> >> >> >> _______________________________________________ >> >> users mailing list >> >> us...@open-mpi.org >> >> http://www.open-mpi.org/mailman/listinfo.cgi/users >> > >> > >> > -- >> > 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 >> > >> >> >> >> -- >> Xianglong Kong >> Department of Mechanical Engineering >> University of Rochester >> Phone: (585)520-4412 >> MSN: dinosaur8...@hotmail.com >> >> _______________________________________________ >> users mailing list >> us...@open-mpi.org >> http://www.open-mpi.org/mailman/listinfo.cgi/users > > > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users > -- Xianglong Kong Department of Mechanical Engineering University of Rochester Phone: (585)520-4412 MSN: dinosaur8...@hotmail.com
