Hi Charles, setContext() is not thread-safe, so if mclapply() is executing in parallel, there will be a race. MPI works across processes, so globals are not shared (and hence setContext() has no problems).
If you want to run multithreaded, you should manage the contexts explicitly. That is, pass a viennacl::context object to the respective constructors of viennacl::vector, viennacl::matrix, etc. You can find examples here: https://github.com/viennacl/viennacl-dev/blob/master/examples/tutorial/multithreaded.cpp https://github.com/viennacl/viennacl-dev/blob/master/examples/tutorial/multithreaded_cg.cpp Best regards, Karli On 05/09/2016 10:32 PM, Charles Determan wrote: > I am trying to use multiple GPU's in parallel using ViennaCL through my > gpuR package. In essence the context is selected at the R level (one > context per device already initialized). Then a matrix is created on > that device. The code looks like this: > > create_matrix <- function(id){ > # sets context > setContext(id) > # create matrix > mat <- vclMatrix(rnorm(16), nrow=4, ncol=4) > return(mat) > } > > # a fork over context 1 and 2 > out <- mclapply(1:2, function(x) create_matrix(x)) > > Yet, strangely this just hangs. It doesn't return anything. Perhaps I > am missing something in how OpenCL contexts are handed in parallel? I > ask as I recall that PETSC had some multi GPU functionality with MPI. > The above makes sense to me without MPI but again I may be missing > something. > > The actual copying happens in this file at line 36 > (https://github.com/cdeterman/gpuR/blob/develop/src/dynVCLMat.cpp) just > after "starting to copy". It seems almost like it a problem with the > class objects (defined in > https://github.com/cdeterman/gpuR/blob/develop/inst/include/gpuR/dynVCLMat.hpp). > > Any insight would be appreciated. > > Regards, > Charles > > > ------------------------------------------------------------------------------ > Mobile security can be enabling, not merely restricting. Employees who > bring their own devices (BYOD) to work are irked by the imposition of MDM > restrictions. Mobile Device Manager Plus allows you to control only the > apps on BYO-devices by containerizing them, leaving personal data untouched! > https://ad.doubleclick.net/ddm/clk/304595813;131938128;j > > > > _______________________________________________ > ViennaCL-devel mailing list > ViennaCL-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/viennacl-devel > ------------------------------------------------------------------------------ Mobile security can be enabling, not merely restricting. Employees who bring their own devices (BYOD) to work are irked by the imposition of MDM restrictions. Mobile Device Manager Plus allows you to control only the apps on BYO-devices by containerizing them, leaving personal data untouched! https://ad.doubleclick.net/ddm/clk/304595813;131938128;j _______________________________________________ ViennaCL-devel mailing list ViennaCL-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/viennacl-devel
