I have a parent process that creates a child via MPI_Comm_spawn(). When the child decides it has to exit, it is hanging in MPI_Finalize(). It does the same if it calls MPI_Comm_disconnect() before MPI_Finalize. Here is the stack trace in the child: (gdb) where #0 0x00007fc6f2fedde0 in __poll_nocancel () from /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/libc.so.6 #1 0x00007fc6f4dc840e in MPID_nem_tcp_connpoll () at src/mpid/ch3/channels/nemesis/netmod/tcp/socksm.c:1819 #2 0x00007fc6f4db857e in MPID_nem_network_poll () at src/mpid/ch3/channels/nemesis/src/mpid_nem_network_poll.c:16 #3 0x00007fc6f4dafc43 in MPIDI_CH3I_Progress () at src/mpid/ch3/channels/nemesis/src/ch3_progress.c:1019 #4 0x00007fc6f4d5094d in MPIDI_CH3U_VC_WaitForClose () at src/mpid/ch3/src/ch3u_handle_connection.c:383 #5 0x00007fc6f4d94efa in MPID_Finalize () at src/mpid/ch3/src/mpid_finalize.c:110 #6 0x00007fc6f4c432ca in PMPI_Finalize () at src/mpi/init/finalize.c:260 #7 0x0000000000408a85 in needles::MpiWorker::finalize () at src/MpiWorker.cpp:470 Maybe I have a communication that hasn't completed, or the child is waiting for the parent to call MPI_Finalize. I believe that you (Ken, Hui) told me that it shouldn't do the latter. Is there a way for the child to cleanly exit without hanging in MPI_Finalize? I tried calling MPI_Cancel() in the child on the only possible communication request that I knew of, but it didn't help. It just occurred to me that I haven't tried calling MPI_Cancel on the requests in the parent... Thanks, Kurt