MPI_Comm_spawn_multiple(3) Open MPI MPI_Comm_spawn_multiple(3)
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
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
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, signifi-
cant 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 (in-
teger).
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, indi-
cates 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 ar-
ray_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 ele-
ments of array_of_argv to MPI_ARGV_NULL is not defined. To specify ar-
guments for some commands but not others, the commands without argu-
ments 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 com-
mands are specified in MPI_Comm_spawn_multiple. Assume that m1 pro-
cesses 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 cor-
responds 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 imple-
mented.)
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 unrecog-
nized, 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 ar-
ray_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 ig-
nored 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 ele-
ment 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.
MPI-3.1 implies (but does not directly state) that the argument ar-
ray_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 ter-
minated 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(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 com-
pletely 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++ 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.
SEE ALSO
MPI_Comm_spawn(3)
MPI_Comm_get_parent(3)
mpirun(1)
4.1.2 Nov 24, 2021 MPI_Comm_spawn_multiple(3)
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