Open MPI logo

MPI_Comm_spawn(3) man page (version 1.3.4)

  |   Home   |   Support   |   FAQ   |  

« Return to documentation listing


       MPI_Comm_spawn - Spawns a number of identical binaries.


C Syntax

       #include <mpi.h>
       int MPI_Comm_spawn(char *command, char *argv[], int maxprocs,
            MPI_Info info, int root, MPI_Comm comm,
            MPI_Comm *intercomm, int array_of_errcodes[])

Fortran Syntax

       INCLUDE 'mpif.h'

            CHARACTER*(*) COMMAND, ARGV(*)

C++ Syntax

       #include <mpi.h>
       MPI::Intercomm MPI::Intracomm::Spawn(const char* command,
            const char* argv[], int maxprocs, const MPI::Info& info,
            int root, int array_of_errcodes[]) const

       MPI::Intercomm MPI::Intracomm::Spawn(const char* command,
            const char* argv[], int maxprocs, const MPI::Info& info,
            int root) const


       command   Name  of  program  to be spawned (string, significant only at

       argv      Arguments to command (array of strings, significant  only  at

       maxprocs  Maximum  number  of  processes to start (integer, significant
                 only at root).

       info      A set of key-value pairs telling the runtime system where and
                 how  to  start  the  processes  (handle,  significant only at

       root      Rank of process in  which  previous  arguments  are  examined

       comm      Intracommunicator  containing  group  of  spawning  processes


       intercomm Intercommunicator  between  original  group  and  the   newly
                 spawned group (handle).

       gram specified by command, establishing  communication  with  them  and
       returning  an  intercommunicator. The spawned processes are referred to
       as children. The children have their own MPI_COMM_WORLD, which is sepa-
       rate  from that of the parents. MPI_Comm_spawn is collective over comm,
       and also may not return until MPI_Init has been called in the children.
       Similarly,  MPI_Init  in  the children may not return until all parents
       have called MPI_Comm_spawn. In this sense, MPI_Comm_spawn in  the  par-
       ents  and MPI_Init in the children form a collective operation over the
       union of parent and child processes. The intercommunicator returned  by
       MPI_Comm_spawn contains the parent processes in the local group and the
       child processes in the remote group. The ordering of processes  in  the
       local and remote groups is the same as the as the ordering of the group
       of the comm in the parents  and  of  MPI_COMM_WORLD  of  the  children,
       respectively.  This  intercommunicator  can be obtained in the children
       through the function MPI_Comm_get_parent.

       The MPI standard allows an implementation to use the  MPI_UNIVERSE_SIZE
       attribute  of  MPI_COMM_WORLD  to  specify the number of processes that
       will be active in a program.  Although this implementation of  the  MPI
       standard  defines  MPI_UNIVERSE_SIZE, it does not allow the user to set
       its value.  If you try to set the value of MPI_UNIVERSE_SIZE, you  will
       get an error message.

       The command Argument

       The command argument is a string containing the name of a program to be
       spawned. The string is null-terminated in C. In  Fortran,  leading  and
       trailing spaces are stripped. MPI looks for the file first in the work-
       ing directory of the spawning process.

       The argv Argument

       argv is an array of strings containing arguments that are passed to the
       program. The first element of argv is the first argument passed to com-
       mand, not, as is conventional in some contexts, the command itself. The
       argument list is terminated by NULL in C and C++ and an empty string in
       Fortran. In Fortran, leading and trailing spaces are  always  stripped,
       so  that  a  string  consisting  of  all  spaces is considered an empty
       string. The constant MPI_ARGV_NULL may be used in C, C++ and Fortran to
       indicate  an  empty  argument  list. In C and C++, this constant is the
       same as NULL.

       In C, the MPI_Comm_spawn argument argv differs from the  argv  argument
       of  main in two respects. First, it is shifted by one element. Specifi-
       cally, argv[0] of main  contains the name of the program (given by com-
       mand).  argv[1]  of  main  corresponds  to  argv[0]  in MPI_Comm_spawn,
       argv[2] of main to argv[1] of MPI_Comm_spawn, and so on.  Second,  argv
       of  MPI_Comm_spawn  must  be null-terminated, so that its length can be
       determined. Passing an argv of MPI_ARGV_NULL to MPI_Comm_spawn  results
       in  main receiving argc of 1 and an argv whose element 0 is the name of
       the program.

       The maxprocs Argument

       Open MPI tries to spawn maxprocs processes. If it is  unable  to  spawn
       maxprocs  processes,  it raises an error of class MPI_ERR_SPAWN. If MPI
       is able to spawn the  specified  number  of  processes,  MPI_Comm_spawn
       returns  successfully  and the number of spawned processes, m, is given
       in C++ and INTEGER in Fortran. It is a container for a number of  user-
       speci  ed (key,value) pairs. key and value are strings (null-terminated
       char* in C, character*(*) in Fortran). Routines to create  and  manipu-
       late the info argument are described in Section 4.10 of the MPI-2 stan-

       For the SPAWN calls, info provides additional, implementation-dependent
       instructions  to  MPI and the runtime system on how to start processes.
       An application may pass MPI_INFO_NULL in C or  Fortran.  Portable  pro-
       grams  not requiring detailed control over process locations should use

       The following keys for info are recognized in Open MPI.  (The  reserved
       values  mentioned in Section 5.3.4 of the MPI-2 standard are not imple-

       Key                   Type      Description
       ---                   ----      -----------

       host                  char *    Host on which the process should be spawned.
                                       See the orte_host man page for an
                                       explanation of how this will be used.
       hostfile              char *    Hostfile containing the hosts on which
                                       the processes are to be spawned. See
                                       the orte_hostfile man page for an
                                       explanation of how this will be used.
       wdir                  char *    Directory where the executable is located.
       ompi_prefix           char *    Same as the --prefix command line argument
                                       to mpirun.
       ompi_non_mpi          bool      If set to true, launching a non-MPI
                                       application; the returned communicator
                                       will be MPI_COMM_NULL. Failure to set
                                       this flag when launching a non-MPI
                                       application will cause both the child
                                       and parent jobs to "hang".

       bool info keys are actually strings but are evaluated  as  follows:  if
       the string value is a number, it is converted to an integer and cast to
       a boolean (meaning that zero integers are false and non-zero values are
       true).   If the string value is (case-insensitive) "yes" or "true", the
       boolean is true.  If the string value  is  (case-insensitive)  "no"  or
       "false",  the  boolean  is false.  All other string values are unrecog-
       nized, and therefore false.

       The root Argument

       All arguments before the root argument are examined only on the process
       whose  rank  in  comm is equal to root. The value of these arguments on
       other processes is ignored.

       The array_of_errcodes Argument

       The array_of_errcodes is an array  of  length  maxprocs  in  which  MPI
       reports the status of the processes that MPI was requested to start. If
       all maxprocs processes were spawned,  array_of_errcodes  is  filled  in
       with  the  value  MPI_SUCCESS.  If anyof the processes are not spawned,
       array_of_errcodes is filled in with the value MPI_ERR_SPAWN.  In  C  or
       intercommunicator can be used immediately).


       Almost  all MPI routines return an error value; C routines as the value
       of the function and Fortran routines in the last  argument.  C++  func-
       tions  do  not  return  errors.  If the default error handler is set to
       MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
       will be used to throw an MPI:Exception object.

       Before  the  error  value is returned, the current MPI error handler is
       called. By default, this error handler aborts the MPI job,  except  for
       I/O   function   errors.   The   error  handler  may  be  changed  with
       MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN
       may  be  used  to cause error values to be returned. Note that MPI does
       not guarantee that an MPI program can continue past an error.



1.3.4                            Nov 11, 2009                MPI_Comm_spawn(3)

« Return to documentation listing