Ubuntu Manpage: MPI_Comm_spawn_multiple - Spawns multiple binaries, or the same binary with multiple sets of arguments.

NAME

       MPI_Comm_spawn_multiple - Spawns multiple binaries, or the same binary with multiple sets of arguments.

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Comm_spawn_multiple(int count, char *array_of_commands[],
            char **array_of_argv[], const int array_of_maxprocs[], const MPI_Info
            array_of_info[], int root, MPI_Comm comm, MPI_Comm *intercomm,
            int array_of_errcodes[])

Fortran Syntax

       INCLUDE 'mpif.h'
       MPI_COMM_SPAWN_MULTIPLE(COUNT, ARRAY_OF_COMMANDS, ARRAY_OF_ARGV,
            ARRAY_OF_MAXPROCS, ARRAY_OF_INFO, ROOT, COMM, INTERCOMM,
            ARRAY_OF_ERRCODES, IERROR)
            INTEGER   COUNT, ARRAY_OF_INFO(*), ARRAY_OF_MAXPROCS(*), ROOT,
                 COMM, INTERCOMM, ARRAY_OF_ERRCODES(*), IERROR
            CHARACTER*(*) ARRAY_OF_COMMANDS(*), ARRAY_OF_ARGV(COUNT, *)

C++ Syntax

       #include <mpi.h>
       MPI::Intercomm MPI::Intracomm::Spawn_multiple(int count,
            const char* array_of_commands[], const char** array_of_argv[],
            const int array_of_maxprocs[], const MPI::Info array_of_info[],
            int root, int array_of_errcodes[])

       MPI::Intercomm MPI::Intracomm::Spawn_multiple(int count,
            const char* array_of_commands[], const char** array_of_argv[],
            const int array_of_maxprocs[], const MPI::Info array_of_info[],
            int root)

INPUT PARAMETERS

       count     Number of commands (positive integer, significant to MPI only at root -- see NOTES).

       array_of_commands
                 Programs to be executed (array of strings, significant only at root).

       array_of_argv
                 Arguments for commands (array of array of strings,  significant only at root).

       array_of_maxprocs
                 Maximum  number  of processes to start for each command (array of integers, significant only at
                 root).

       array_of_info
                 Info objects telling the runtime system where and how to start  processes  (array  of  handles,
                 significant only at root).

       root      Rank of process in which previous arguments are examined (integer).

       comm      Intracommunicator containing group of spawning processes (handle).

OUTPUT PARAMETERS

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

       array_of_errcodes
                 One code per process (array of integers).

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

MPI_Comm_spawn_multiple is identical to MPI_Comm_spawn(3) except that it can specify multiple
executables. The first argument, count, indicates the number of executables. The next three arguments are
arrays of the corresponding arguments in MPI_Comm_spawn(3). The next argument, array_of_info, is an array
of info arguments, one for each executable. See the INFO ARGUMENTS section for more information.

For the Fortran version of array_of_argv, the element array_of_argv(i,j) is the jth argument to command
number i.

In any language, an application may use the constant MPI_ARGVS_NULL (which is likely to be (char ***)0 in
C) to specify that no arguments should be passed to any commands. The effect of setting individual
elements of array_of_argv to MPI_ARGV_NULL is not defined. To specify arguments for some commands but not
others, the commands without arguments should have a corresponding argv whose first element is null
((char *)0 in C and empty string in Fortran).

All of the spawned processes have the same MPI_COMM_WORLD. Their ranks in MPI_COMM_WORLD correspond
directly to the order in which the commands are specified in MPI_Comm_spawn_multiple. Assume that m1
processes are generated by the first command, m2 by the second, etc. The processes corresponding to the
first command have ranks 0, 1,..., m1-1. The processes in the second command have ranks m1, m1+1, ...,
m1+m2-1. The processes in the third have ranks m1+m2, m1+m2+1, ..., m1+m2+m3-1, etc.

The array_of_errcodes argument is 1-dimensional array of size

_ count
\ n ,
/_ i=1 i

where i is the ith element of array_of_maxprocs. Command number i corresponds to the i contiguous slots
in this array from element

_ _
_ i-1 | _ i |
\ n , to | \ n | -1
/_ j=1 i | /_ j=1 j |
|_ _|

Error codes are treated as for MPI_Comm_spawn(3).

INFO ARGUMENTS

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 implemented.)

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

host char * Comma-separated list of hosts on which
the processes 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.
add-host char * Add the specified hosts to the list of
hosts known to this job and use it for
the associated processes. This will be
used similarly to the -host option.
add-hostfile char * Hostfile containing hosts to be added
to the list of hosts known to this job
and use it for the associated
process. This will be used similarly
to the -hostfile option.
wdir char * Directory where the executable is
located. If files are to be
pre-positioned, then this location is
the desired working directory at time
of execution - if not specified, then
it will automatically be set to
ompi_preload_files_dest_dir.
ompi_prefix char * Same as the --prefix command line
argument to mpirun.
ompi_preload_binary bool If set to true, pre-position the
specified executable onto the remote
host. A destination directory must
also be provided.
ompi_preload_files char * A comma-separated list of files that
are to be pre-positioned in addition
to the executable. Note that this
option does not depend upon
ompi_preload_binary - files can
be moved to the target even if an
executable is not moved.
ompi_stdin_target char* Comma-delimited list of ranks to
receive stdin when forwarded.
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".
ompi_param char * Pass an OMPI MCA parameter to the
child job. If that parameter already
exists in the environment, the value
will be overwritten by the provided
value.
mapper char* Mapper to be used for this job
map_by char* Mapping directive indicating how
processes are to be mapped (slot,
node, socket, etc.).
rank_by char * Ranking directive indicating how
processes are to be ranked (slot,
node, socket, etc.).
bind_to char * Binding directive indicating how
processes are to be bound (core, slot,
node, socket, etc.).
path char* List of directories to search for
the executable
npernode char* Number of processes to spawn on
each node of the allocation
pernode bool Equivalent to npernode of 1
ppr char* Spawn specified number of processes
on each of the identified object type
env char* Newline-delimited list of envars to
be passed to the spawned procs

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
unrecognized, and therefore false.

Note that if any of the info handles have ompi_non_mpi set to true, then all info handles must have it
set to true. If some are set to true, but others are set to false (or are unset), MPI_ERR_INFO will be
returned.

Note that in "Open MPI", the first array location in array_of_info is applied to all the commands in
array_of_commands.

NOTES

The argument count is interpreted by MPI only at the root, as is array_of_argv. Since the leading
dimension of array_of_argv is count, a nonpositive value of count at a nonroot node could theoretically
cause a runtime bounds check error, even though array_of_argv should be ignored by the subroutine. If
this happens, you should explicitly supply a reasonable value of count on the nonroot nodes.

Similar to MPI_Comm_spawn(3), it is the application's responsibility to terminate each individual set of
argv in the array_of_argv argument. In C, each argv array is terminated by a NULL pointer. In Fortran,
each argv array is terminated by an empty string (note that compilers will not automatically insert this
blank string; the application must ensure to have enough space for an empty string entry as the last
element of the array).

Other restrictions apply to the array_of_argv parameter; see MPI_Comm_spawn(3)'s description of the argv
parameter for more details.

Calling MPI_Comm_spawn(3) many times would create many sets of children with different MPI_COMM_WORLDs,
whereas MPI_Comm_spawn_multiple creates children with a single MPI_COMM_WORLD, so the two methods are not
completely equivalent. Also if you need to spawn multiple executables, you may get better performance by
using MPI_Comm_spawn_multiple instead of calling MPI_Comm_spawn(3) several times.

ERRORS

       Almost  all  MPI  routines  return  an  error  value; C routines as the value of the function and Fortran
       routines in the last argument. C++ functions 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.