plucky (3) MPI_Comm_spawn_multiple.openmpi.3.gz
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
USE MPI
! or the older form: 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, *)
Fortran 2008 Syntax
USE mpi_f08
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, INTENT(IN) :: count, array_of_maxprocs(*), root
CHARACTER(LEN=*), INTENT(IN) :: array_of_commands(*)
CHARACTER(LEN=*), INTENT(IN) :: array_of_argv(count, *)
TYPE(MPI_Info), INTENT(IN) :: array_of_info(*)
TYPE(MPI_Comm), INTENT(IN) :: comm
TYPE(MPI_Comm), INTENT(OUT) :: intercomm
INTEGER :: array_of_errcodes(*)
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
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 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. 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.
INFO ARGUMENTS
The following keys for info are recognized in “#PACKAGE_NAME#”. (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 “#PACKAGE_NAME#”, 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, 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’s description of the argv
parameter for more details.
MPI-3.1 implies (but does not directly state) that the argument array_of_commands must be an array of
strings of length count. Unlike the array_of_argv parameter, array_of_commands does not need to be
terminated with a NULL pointer in C or a blank string in Fortran. Older versions of Open MPI required
that array_of_commands be terminated with a blank string in Fortran; that is no longer required in this
version of Open MPI.
Calling MPI_Comm_spawn 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 several times.
ERRORS
Almost all MPI routines return an error value; C routines as the return result of the function and
Fortran routines in the last argument.
Before the error value is returned, the current MPI error handler associated with the communication
object (e.g., communicator, window, file) is called. If no communication object is associated with the
MPI call, then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error
handler. When MPI_COMM_SELF is not initialized (i.e., before MPI_Init/MPI_Init_thread, after
MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial error handler.
The initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using
the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/‐
MPI_Comm_spawn_multiple. If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all
other MPI functions.
Open MPI includes three predefined error handlers that can be used:
• MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.
• MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
called on a communicator, it acts as if MPI_Abort was called on that communicator. If called on a
window or file, acts as if MPI_Abort was called on a communicator containing the group of processes in
the corresponding window or file. If called on a session, aborts only the local process.
• MPI_ERRORS_RETURN Returns an error code to the application.
MPI applications can also implement their own error handlers by calling:
• MPI_Comm_create_errhandler then MPI_Comm_set_errhandler
• MPI_File_create_errhandler then MPI_File_set_errhandler
• MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init
• MPI_Win_create_errhandler then MPI_Win_set_errhandler
Note that MPI does not guarantee that an MPI program can continue past an error.
See the MPI man page for a full list of MPI error codes.
See the Error Handling section of the MPI-3.1 standard for more information.
SEE ALSO:
• MPI_Comm_spawn
• MPI_Comm_get_parent
• mpirun(1)
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Feb 17, 2025 MPI_COMM_SPAWN_MULTIPLE(3)