I posted this question on StackOverflow and someone suggested I write to the OpenMPI community.
https://stackoverflow.com/questions/62223698/mpi-i-o-why-does-my-program-hang-or-misbehave-when-one-process-writes-using-mpi Below is a little MPI program. It is a simple use of MPI I/O. Process 0 writes an int to the file using MPI_File_write_shared; no other process writes anything. It works correctly using an MPICH installation, but on two different machines using OpenMPI, it either hangs in the middle of the call to MPI_File_write_shared, or it reports an error at the end. Not sure if it is my misunderstanding of the MPI Standard or a bug or configuration problem with my OpenMPI. Thanks in advance if anyone can look at it, Steve #include <stdio.h> #include <mpi.h> #include <assert.h> int nprocs, rank; int main() { MPI_File fh; int err, count; MPI_Status status; MPI_Init(NULL, NULL); MPI_Comm_size(MPI_COMM_WORLD, &nprocs); MPI_Comm_rank(MPI_COMM_WORLD, &rank); err = MPI_File_open(MPI_COMM_WORLD, "io_byte_shared.tmp", MPI_MODE_CREATE | MPI_MODE_WRONLY, MPI_INFO_NULL, &fh); assert(err==0); err = MPI_File_set_view(fh, 0, MPI_INT, MPI_INT, "native", MPI_INFO_NULL); assert(err==0); printf("Proc %d: file has been opened.\n", rank); fflush(stdout); // Proc 0 only writes header using shared file pointer... MPI_Barrier(MPI_COMM_WORLD); if (rank == 0) { int x = 9999; printf("Proc 0: About to write to file.\n"); fflush(stdout); err = MPI_File_write_shared(fh, &x, 1, MPI_INT, &status); printf("Proc 0: Finished writing.\n"); fflush(stdout); assert(err == 0); } MPI_Barrier(MPI_COMM_WORLD); printf("Proc %d: about to close file.\n", rank); fflush(stdout); err = MPI_File_close(&fh); assert(err==0); MPI_Finalize(); } Example run: $ mpicc io_byte_shared.c $ mpiexec -n 4 ./a.out Proc 0: file has been opened. Proc 0: About to write to file. Proc 0: Finished writing. Proc 1: file has been opened. Proc 2: file has been opened. Proc 3: file has been opened. Proc 0: about to close file. Proc 1: about to close file. Proc 2: about to close file. Proc 3: about to close file. [ilyich:12946] 3 more processes have sent help message help-mpi-btl-base.txt / btl:no-nics [ilyich:12946] Set MCA parameter "orte_base_help_aggregate" to 0 to see all help / error messages
