Hi, Since this is a conversation on thread support, I have a quick related question. Is MPI_THREAD_MULTIPLE supported with OpenMPI's Java binding?
Thank you, Saliya On Wed, Oct 23, 2013 at 2:40 PM, Jeff Hammond <jeff.scie...@gmail.com>wrote: > And in practice the difference between FUNNELED and SERIALIZED will be > very small. The differences might emerge from thread-local state and > thread-specific network registration, but I don't see this being > required. Hence, for most purposes SINGLE=FUNNELED=SERIALIZED is > equivalent to NOMUTEX and MULTIPLE is MUTEX, where MUTEX refers to the > internal mutex required to make MPI reentrant. > > Jeff > > On Wed, Oct 23, 2013 at 1:18 PM, Tim Prince <n...@aol.com> wrote: > > On 10/23/2013 01:02 PM, Barrett, Brian W wrote: > > > > On 10/22/13 10:23 AM, "Jai Dayal" <dayals...@gmail.com> wrote: > > > > I, for the life of me, can't understand the difference between these two > > init_thread modes. > > > > MPI_THREAD_SINGLE states that "only one thread will execute", but > > MPI_THREAD_FUNNELED states "The process may be multi-threaded, but only > the > > main thread will make MPI calls (all MPI calls are funneled to the main > > thread)." > > > > If I use MPI_THREAD_SINGLE, and just create a bunch of pthreads that > dumbly > > loop in the background, the MPI library will have no way of detecting > this, > > nor should this have any affects on the machine. > > > > This is exactly the same as MPI_THREAD_FUNNELED. What exactly does it > mean > > with "only one thread will execute?" The openmpi library has absolutely > zero > > way of knowng I've spawned other pthreads, and since these pthreads > aren't > > actually doing MPI communication, I fail to see how this would interfere. > > > > > > Technically, if you call MPI_INIT_THREAD with MPI_THREAD_SINGLE, you have > > made a promise that you will not create any other threads in your > > application. There was a time where OSes shipped threaded and > non-threaded > > malloc, for example, so knowing that might be important for that last > bit of > > performance. There are also some obscure corner cases of the memory > model > > of some architectures where you might get unexpected results if you made > an > > MPI Receive call in an thread and accessed that buffer later from another > > thread, which may require memory barriers inside the implementation, so > > there could be some differences between SINGLE and FUNNELED due to those > > barriers. > > > > In Open MPI, we'll handle those corner cases whether you init for SINGLE > or > > FUNNELED, so there's really no practical difference for Open MPI, but > you're > > then slightly less portable. > > > > I'm asking because I'm using an open_mpi build ontop of infiniband, and > the > > maximum thread mode is MPI_THREAD_SINGLE. > > > > > > That doesn't seem right; which version of Open MPI are you using? > > > > Brian > > > > > > > > As Brian said, you aren't likely to be running on a system like Windows > 98 > > where non-thread-safe libraries were preferred. My colleagues at NASA > > insist that any properly built MPI will support MPI_THREAD_FUNNELED by > > default, even when the documentation says explicit setting in > > MPI_Init_thread() is mandatory. The statement which I see in OpenMPI doc > > says all MPI calls must be made by the thread which calls > MPI_Init_thread. > > Apparently it will work if plain MPI_Init is used instead. This theory > > appears to hold up for all the MPI implementations of interest. The > > additional threads referred to are "inside the MPI rank," although I > suppose > > additional application threads not involved with MPI are possible. > > > > > > _______________________________________________ > > users mailing list > > us...@open-mpi.org > > http://www.open-mpi.org/mailman/listinfo.cgi/users > > > > -- > Jeff Hammond > jeff.scie...@gmail.com > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users > -- Saliya Ekanayake esal...@gmail.com Cell 812-391-4914 Home 812-961-6383 http://saliya.org
