You're right, in v1.2 it will return MPI_THREAD_SINGLE (although it really shouldn't). Some MPI implementations may do something different if you request MPI_THREAD_FUNNELED instead of MPI_THREAD_SINGLE, so you should continue to do that. A future version of Open MPI will return the provided as MPI_THREAD_FUNNELED in that case instead of MPI_THREAD_SINGLE. But you can safely use two threads as you describe even with the provided of MPI_THREAD_SINGLE.
Brian > I tried with MPI_THREAD_FUNNELED but it still returns MPI_THREAD_SINGLE > in "provided". I tried a sample program that has thread_0 doing MPI and > thread_1 doing some computation and thread_0 and thread_1 doing some > thread synchronization (using pthread condition variables). The program > seems to be doing fine and so also the thread synchronization. I think, > even if MPI_THREAD_SINGLE is returned in provided, such a design works. > Now, since the thread synchronization seems to be fine, I think multiple > threads (with only one thread executing MPI calls) works even if > "provided" returns MPI_THREAD_SINGLE. > > -Thanks and Regards, > Sarang. > > Quoting "Brian W. Barrett" <bbarr...@lanl.gov>: > >> If only one thread ever makes calls into MPI, you don't actually >> need >> MPI_THREAD_MULTIPLE but only MPI_THREAD_FUNNELED. Open MPI will >> generally >> support MPI_THREAD_FUNNELED out of the box (but on certain >> configurations, >> mainly platforms without threads, will not), so if you request >> MPI_THREAD_FUNNELED, it should be returned in provided. >> >> Good luck, >> >> Brian >> >> > Thanks a lot guys for your help. I am also trying a design where I >> have >> > one thread doing MPI and others doing some computation (non-MPI). >> If I >> > have only MPI_THREAD_SINGLE enabled for OpenMPI, can I still >> implement >> > this kind of a design or there would be issues with threads in >> OpenMPI. >> > >> > -Thanks and Regards, >> > Sarang. >> > >> > Quoting "Brian W. Barrett" <bbarr...@lanl.gov>: >> > >> >> There are two ways you can find out if an Open MPI build has >> >> MPI_THREAD_MULTIPLE support: >> >> >> >> * On the command line: You can run "ompi_info | grep Thread". If >> you >> >> see >> >> mpi: no, the build doesn't support MPI_THREAD_MULTIPLE. If you >> see >> >> mpi: >> >> yes, the build does support MPI_THREAD_MULTIPLE. >> >> >> >> * At run-time. As mentioned below, if you request >> >> MPI_THREAD_MULTIPLE and >> >> provided is only MPI_THREAD_SINGLE, then Open MPI does not have >> >> MPI_THREAD_MULTIPLE support. >> >> >> >> >> >> Good luck, >> >> >> >> Brian >> >> >> >> > You are already there. the fact that MPI_Thread_init only >> provide >> >> > MPI_THREAD_SINGLE shows that MPI_THREAD_MULTIPLE is NOT enabled >> in >> >> the >> >> > library binary that you're using. Although MPI_THREAD_MULTIPLE >> is >> >> > implemented in the library source code, it is only lightly >> tested, >> >> so it >> >> > is >> >> > not enabled by default. >> >> > >> >> > To enable MPI_THREAD_MULTIPLE, you need to recompile the library >> by >> >> first >> >> > including --enable-mpi-threads as one of the parameters when you >> >> rerun >> >> > ./configure as the first step of recompiling the library. >> >> > >> >> > >> >> > >> >> > On 5/27/07, smai...@ksu.edu <smai...@ksu.edu> wrote: >> >> >> >> >> >> Hi, >> >> >> I want to use threads with OpenMPI such that the >> threads >> >> would >> >> >> be able to call MPI functions. For this purpose, I am using >> >> >> MPI_Init_thread with MPI_THREAD_MULTIPLE option. But this >> function >> >> call >> >> >> returns MPI_THREAD_SINGLE in the "provided" parameter >> indicating >> >> that >> >> >> MPI_THREAD_MULTIPLE is not configured. Somewhere it is >> mentioned >> >> that >> >> >> OpenMPI needs to be configured with --enable-mpi-threads >> inorder >> >> to use >> >> >> MPI_THREAD_MULTIPLE. If true, is it possible to know whether >> the >> >> >> OpenMPI (1.1.2)which I have already configured, has the option >> >> >> "--enable-mpi-threads" already configured or not? Also, how >> easy >> >> or >> >> >> difficult is it to configure --enable-mpi-threads option? >> >> >> Please share some information on this. >> >> >> >> >> >> -Thanks and Regards, >> >> >> Sarang. >> >> >> >> >> >> >> >> >> _______________________________________________ >> >> >> 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 >> >> >> >> _______________________________________________ >> >> users mailing list >> >> us...@open-mpi.org >> >> http://www.open-mpi.org/mailman/listinfo.cgi/users >> >> >> >> >> > >> > >> > >> >> > > >
