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

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[], int array_of_maxprocs[], 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 processes. 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_local_slave bool If set to true, launch the specified process
as a local slave to the calling process.
The new process will only be known to the caller,
and will only be able to communicate with the caller.
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_dest_dir char * Target directory where pre-positioned files
are to be placed.
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_preload_files_src_dir char * Source directory where files and executables
that are to be pre-positioned can be found. If
not specified, the current working directory
will be used.
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.
map_bynode bool If set to true, the processes are mapped bynode.
If set to false, the processes are mapped byslot.
By default, mapping is determined by the default
mapping policy set when the job was started.

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.