Hi, Using mpich-3.1.2, we are trying to create a multi-process multi-node MPI job with the client-server model but we are having issues creating the global communicator we need. We cannot use mpiexec to launch the MPI processes; they are launched by a different daemon and we want them to join a group and use MPI after they are launched. We chose to use a server to publish a name/port and wait on a known number of clients to connect. The goal is to create an intracommunicator among all the clients and the server, and start normal MPI communication (not sure whether there is a better way to accomplish this goal?). *The problem *is that the first client connects fine, but the subsequent clients block. The *simplified method *that we are using is here: * ------------------- Server -----------------* - Call *MPI_Open_port(MPI_INFO_NULL, port_name)* - Call *MPI_Publish_name(service_name, MPI_INFO_NULL, port_name)* - clients = 0 Loop until clients = MAX_CLIENTS: if ( !clients ) - Call *MPI_Comm_accept(port_name,MPI_INFO_NULL,0,MPI_COMM_FELF,&new_ircomm)* else - Call *MPI_Comm_accept(port_name,MPI_INFO_NULL,0,previous_iacomm,&new_ircomm)* - Call *MPI_Intercomm_merge(new_ircomm, 0, &new_iacomm)* - previous_iacomm = new_iacomm - clients ++ end Loop *---------------- Client ---------------* - Call *MPI_Lookup_name(service_name, MPI_INFO_NULL, port_name)* - Call *MPI_Comm_connect(port_name, MPI_INFO_NULL, 0, MPI_COMM_SELF, &new_ircomm)* - Call *MPI_Intercomm_merge(new_ircomm, 1 , &new_iacomm)* - previous_iacomm *= *new_iacomm Loop for all clients connecting after me: - Call *MPI_Comm_accept(port_name,MPI_INFO_NULL,0,previous_iacomm,&new_ircomm)* - Call *MPI_Intercomm_merge(new_ircomm, 0, &new_iacomm)* - previous_iacomm = new_iacomm end Loop ---------------------------------- *Note *that MPI report states that MPI_Comm_accept is collective over the calling communicator, that's why we are calling it by the server and all previously connected clients. *The problem we are having *is that the first client connects fine, but the subsequent clients block on MPI_Comm_connect. Also the server and previously connected clients block on MPI_Comm_accept. (the server does not block only if we use MPI_COMM_SELF for all accept calls, but that does not help us creating the global intracomm that we want. I suspect that we are missing something in our usage of MPI_Comm_accept. Any insight is helpful and appreciated. I can send the actual C code if needed. Thanks Mohammad _______________________________________________ discuss mailing list [email protected] To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss