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MPI_Comm_spawn - Spawns a number of identical binaries.
#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[])
INCLUDE ’mpif.h’
MPI_COMM_SPAWN(COMMAND, ARGV, MAXPROCS, INFO, ROOT, COMM,
INTERCOMM, ARRAY_OF_ERRCODES, IERROR)
CHARACTER*(*) COMMAND, ARGV(*)
INTEGER INFO, MAXPROCS, ROOT, COMM, INTERCOMM,
ARRAY_OF_ERRCODES(*), IERROR
#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 root).
- argv
- Arguments to command (array of strings, significant
only at root).
- 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).
- root
- Rank of process in which previous arguments are examined (integer).
- comm
- Intracommunicator containing group of spawning processes (handle).
- 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).
MPI_Comm_spawn
tries to start maxprocs identical copies of the MPI program 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 separate 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 parents 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 working 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
command, 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 (note that it is the MPI application’s responsibility to ensure
that the last entry of the argv array is an empty string; the compiler
will not automatically insert it). 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. Specifically,
argv[0] of main contains the name of the program (given by command). 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 by the size of the remote group of intercomm.
A spawn
call with the default behavior is called hard. A spawn call for which fewer
than maxprocs processes may be returned is called soft.
The info Argument
The info argument is an opaque handle of type MPI_Info in C, MPI::Info
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 manipulate the info
argument are described in Section 4.10 of the MPI-2 standard.
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 programs not requiring detailed
control over process locations should use MPI_INFO_NULL.
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 * 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.
add-host char * Add the specified host to the
list of
hosts known to this job and use
it
for the associated process. 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_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.
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 Fortran, an application may pass MPI_ERRCODES_IGNORE
if it is not interested in the error codes. In C++ this constant does not
exist, and the array_of_errcodes argument may be omitted from the argument
list.
Completion of MPI_Comm_spawn in the parent does not necessarily
mean that MPI_Init has been called in the children (although the returned
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++ 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.
MPI_Comm_spawn_multiple(3)
MPI_Comm_get_parent(3)
mpirun(1)
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