Hello, I have been experimenting with mpich’s implementation of one-sided communication with no remote synchronization that was introduced in the mpi3.0 spec and I have run into a hang issue during connect/accept MPI scenarios. Here is the situation, I have two applications that connect to each other after they have been launched separately with mpiexec on two different hosts. After connecting, both hosts allocate memory and run MPI_Win_Create as the following: Host1_program: void* buffer = mmap(0, buf_length, PROT_READ | PROT_WRITE, MAP_SHARED|MAP_POPULATE|MAP_ANON, -1, 0); MPI_Intercomm_merge(connected_comm, 1, &comm); MPI_Comm_rank(comm, &myrank); MPI_Win_create(NULL, 0, 1, MPI_INFO_NULL, comm, &win); Host2_program: void* buffer = mmap(0, buf_length, PROT_READ | PROT_WRITE, MAP_SHARED|MAP_POPULATE|MAP_ANON, -1, 0); MPI_Intercomm_merge(connected_comm, 1, &comm); MPI_Comm_rank(comm, &myrank); MPI_Win_create(buffer, buf_length, 1, MPI_INFO_NULL, comm, &win); Once the MPI_Window has been created I execute the following on host1: Host1_program(continued): err = MPI_Win_lock(MPI_LOCK_SHARED, target_rank, 0, win); if(err != MPI_SUCCESS) { return 1; } err = MPI_Put(buffer, buf_length, MPI_BYTE, target_rank, 0, buf_length, MPI_BYTE, win); if(err != MPI_SUCCESS) { return 1; } err = MPI_Win_flush(target_rank, win); if(err != MPI_SUCCESS) { return 1; } err = MPI_Win_unlock(target_rank, win); if(err != MPI_SUCCESS) { return 1; } While this is running, host2’s program is simply sleeping in a getchar(). This should run and complete, however, if the other host has not called another mpi function such as MPI_Recv and instead is in a sleep, getchar(), etc. the MPI_Win_flush above will simply hang. Why is the one-sided operation hanging until another MPI operation is called on the target host? My understanding is that utilizing MPI_Win_Flush does not require any action by the target host to complete the operation. This is a stack trace of where the flush gets stuck: #0 0x0000003b456dea28 in poll () from /lib64/libc.so.6 #1 0x00007fe1c08004ee in MPID_nem_tcp_connpoll () from /usr/local/lib/libmpich.so.12 #2 0x00007fe1c07efab7 in MPIDI_CH3I_Progress () from /usr/local/lib/libmpich.so.12 #3 0x00007fe1c07d35ff in MPIDI_CH3I_Wait_for_lock_granted () from /usr/local/lib/libmpich.so.12 #4 0x00007fe1c07d88bf in MPIDI_Win_flush () from /usr/local/lib/libmpich.so.12 #5 0x00007fe1c08c1b46 in PMPI_Win_flush () from /usr/local/lib/libmpich.so.12 #6 0x000000000040115c in main () According to this it seems that somehow the remote host is holding something after MPI_Win_Create that in my scenario gets unlocked if I call MPI_Recv on the connected_comm from above after the MPI_Win_Create. Thank you for your time and I look forward to your reply. Respectfully, Neil Spruit P.S. MPICH version info Version: 3.1 Release Date: Thu Feb 20 11:41:13 CST 2014 _______________________________________________ discuss mailing list [email protected] To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss