MPI_COMM_SPAWN_MULTIPLE(3)			     Open MPI				MPI_COMM_SPAWN_MULTIPLE(3)

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

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  <#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 <#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 <#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 <#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 <#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	<#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	<#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>/MPI_Init_thread <#mpi-init-thread>,
       after MPI_Finalize <#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 <#
       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>/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 <#mpi-abort> was called on that communicator. If called
	 on a window or file, acts as if MPI_Abort <#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	 <#mpi-comm-create-errhandler>	   then	    MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	<#mpi-file-create-errhandler>	  then	   MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

       See the Error Handling section of the MPI-3.1 standard for more information.

       See also:

	  • MPI_Comm_spawn <#mpi-comm-spawn>

	  • MPI_Comm_get_parent <#mpi-comm-get-parent>

	  • mpirun(1) <#man1-mpirun>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026				MPI_COMM_SPAWN_MULTIPLE(3)
