Simple Chat program C++ in MPI -
my program includes 1 rank process of server , 1 rank process of client. client transfer number (array of type double) server.
here code
//server rank if (rank == 0){ double buf[max_data]; mpi_open_port(mpi_info_null, port_name); printf("server available @ %s\n", port_name); while (1) { mpi_comm_accept(port_name, mpi_info_null, 0, mpi_comm_world, &client); again = 1; while (again) { mpi_recv(buf, max_data, mpi_double, 0, mpi_any_tag, client, &status); switch (status.mpi_tag) { case 0: mpi_comm_free(&client); mpi_close_port(port_name); mpi_finalize(); return 0; case 1: mpi_comm_disconnect(&client); again = 0; break; case 2: /* */ printf("case 2\n"); break; default: /* unexpected message type */ mpi_abort(mpi_comm_world, 1); } } } } // client rank else { mpi_comm server; double buf[max_data]; mpi_comm_connect(port_name, mpi_info_null, 0, mpi_comm_world, &server); int = 0; while (true) { int tag = 2; /* action perform */ mpi_send(buf, max_data, mpi_double, 0, tag, server); } mpi_send(buf, 0, mpi_double, 0, 1, server); mpi_comm_disconnect(&server); } mpi_finalize(); but code doesn't work, , stucked when type command "mpiexec -n 2 mpi_helloworld.exe" (there 2 processes created run program)
i modify code source : "http://www.mcs.anl.gov/research/projects/mpi/mpi-standard/mpi-report-2.0/node106.htm"
program's result: gets stucks: server doesnot receive message 
few things:
1) server needs tell client port accepting communications on. so, before starting accept needs send message client , tell client port_name.
so, call needed:
mpi_send(port_name, mpi_max_port_name, mpi_char, 1, 0, mpi_comm_world); and client needs receive message. so, client first needs do:
mpi_recv(port_name, mpi_max_port_name, mpi_char, 0, 0, mpi_comm_world, &status); 2) client/server requires point-to-point communication (you have multiple clients between 2 processes @ same time), cannot use mpi_comm_world(which includes processes) in mpi_comm_accept() , mpi_comm_connect(). correct communicator use mpi_comm_self.
so calls need changed to:
mpi_comm_accept(port_name, mpi_info_null, 0, mpi_comm_self, &client); and
mpi_comm_connect(port_name, mpi_info_null, 0, mpi_comm_self, &server); the following code has been tested on system , runs:
#include <stdio.h> #include <mpi.h> #define max_data 100 int main (int argc, char *argv[]){ int rank, size; char port_name[mpi_max_port_name]; mpi_init (&argc, &argv); /* starts mpi */ mpi_comm_rank (mpi_comm_world, &rank); /* current process id */ mpi_comm_size (mpi_comm_world, &size); /* number of processes */ //server rank if (rank == 0){ double buf[max_data]; mpi_open_port(mpi_info_null, port_name); printf("server available @ %s\n", port_name); // server tells client port_name mpi_send(port_name, mpi_max_port_name, mpi_char, 1, 0, mpi_comm_world); mpi_comm client; mpi_status status; while (1) { mpi_comm_accept(port_name, mpi_info_null, 0, mpi_comm_self, &client); int again = 1; while (again) { mpi_recv(buf, max_data, mpi_double, 1, mpi_any_tag, client, &status); printf("server received sth!\n"); switch (status.mpi_tag) { case 0: mpi_comm_free(&client); mpi_close_port(port_name); mpi_finalize(); return 0; case 1: mpi_comm_disconnect(&client); again = 0; break; case 2: /* */ printf("case 2\n"); break; default: /* unexpected message type */ mpi_abort(mpi_comm_world, 1); } } } } else{ mpi_status status; // client receives port information server mpi_recv(port_name, mpi_max_port_name, mpi_char, 0, 0, mpi_comm_world, &status); mpi_comm server; double buf[max_data]; mpi_comm_connect(port_name, mpi_info_null, 0, mpi_comm_self, &server); int = 0; while (1) { int tag = 2; /* action perform */ mpi_send(buf, max_data, mpi_double, 0, tag, server); printf("client send somthing!\n"); sleep(1); } mpi_send(buf, 0, mpi_double, 0, 1, server); mpi_comm_disconnect(&server); } mpi_finalize(); }
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