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RedHat 9 (Linux i386) - man page for mpi_comm_spawn_multiple (redhat section 3)

MPI_Comm_spawn_multiple(3)		     LAM/MPI		       MPI_Comm_spawn_multiple(3)

       MPI_Comm_spawn_multiple -  Spawn a dynamic MPI process from multiple executables

       #include <mpi.h>
       MPI_Comm_spawn_multiple(int count, char **commands, char ***argvs,
	  int *maxprocs, MPI_Info *infos, int root,
	  MPI_Comm comm, MPI_Comm *intercomm,
	  int *errcodes)

       count  - number of commands (only significant at root)
	      - commands to be executed (only significant at root)
       argvs  - arguments for commands (only significant at root)
	      - max number of processes for each command (only significant at root)
       infos  - startup hints for each command
       root   - rank of process to perform the spawn
       comm   - parent intracommunicator

	      - child intercommunicator containing spawned processes
	      - one code per process

       A group of processes can create another group of processes with MPI_Comm_spawn_multiple
	.  This function is a collective operation over the parent communicator.  The child group
       starts up like any MPI application.  The processes must begin by calling MPI_Init ,  after
       which the pre-defined communicator, MPI_COMM_WORLD , may be used.  This world communicator
       contains only the child processes.  It is distinct from the MPI_COMM_WORLD of  the  parent

       MPI_Comm_spawn_multiple	is  used to manually specify a group of different executables and
       arguments to spawn.  MPI_Comm_spawn is used to specify one executable and set of arguments
       (although  a  LAM/MPI  appschema(5)  can be provided to MPI_Comm_spawn via the "file" info

       Communication With Spawned Processes

       The natural communication mechanism between two groups is the intercommunicator.  The sec-
       ond  communicator  argument  to MPI_Comm_spawn_multiple returns an intercommunicator whose
       local group contains the parent processes (same as the first  communicator  argument)  and
       whose  remote  group  contains  child  processes.  The child processes can access the same
       intercommunicator by using the MPI_Comm_get_parent call.  The remote  group  size  of  the
       parent communicator is zero if the process was created by mpirun (1) instead of one of the
       spawn functions.  Both groups can decide to merge the intercommunicator into an	intracom-
       municator (with the MPI_Comm_merge () function) and take advantage of other MPI collective
       operations.  They can then use the merged intracommunicator to  create  new  communicators
       and reach other processes in the MPI application.

       Resource Allocation

       Note  that no MPI_Info keys are recognized by this implementation of MPI_Comm_spawn_multi-
	.  To use the "file" info key to specify an appschema(5), use LAM's MPI_Comm_spawn
	.  This may be preferable to MPI_Comm_spawn_multiple  because  it  allows  the	arbitrary
       specification  of  what	nodes  and/or  CPUs should be used to launch jobs (either SPMD or
       MPMD).  See MPI_Comm_spawn(3) for more details.

       The value of MPI_INFO_NULL should be given for each value in infos (the infos array is not
       currently  examined  by LAM/MPI, so specifying non-NULL values for the array values is not
       harmful).  LAM schedules the given number of processes onto LAM nodes by starting with CPU
       0  (or  the  lowest  numbered CPU), and continuing through higher CPU numbers, placing one
       process on each CPU.  If the process count is greater than the CPU  count,  the	procedure

       Process Count

       The maxprocs array parameter to MPI_Comm_spawn_multiple specifies the exact number of pro-
       cesses to be started.  If it is not possible to start the  desired  number  of  processes,
       MPI_Comm_spawn_multiple will return an error code.  Note that even though maxprocs is only
       relevant on the root, all ranks must have an errcodes array long enough to handle an inte-
       ger   error   code  for	every  process	that  tries  to  launch,  or  give  MPI  constant
       MPI_ERRCODES_IGNORE for the errcodes argument.  While this appears to be a  contradiction,
       it is per the MPI-2 standard.  :-\

       Frequently,  an application wishes to chooses a process count so as to fill all processors
       available to a job.  MPI indicates the maximum number of processes recommended for  a  job
       in the pre-defined attribute, MPI_UNIVERSE_SIZE , which is cached on MPI_COMM_WORLD
	.   The  typical  usage  is to subtract the value of MPI_UNIVERSE_SIZE from the number of
       processes currently in the job and spawn the difference.  LAM  sets  MPI_UNIVERSE_SIZE  to
       the number of CPUs in the user's LAM session (as defined in the boot schema [bhost(5)] via
       lamboot (1)).

       Locating an Executable Program

       The executable program file must be located on the node(s) where the process(es) will run.
       On  any	node,  the  directories  specified  by	the  user's PATH environment variable are
       searched to find the program.

       All MPI runtime options selected by mpirun (1) in the initial application launch remain in
       effect for all child processes created by the spawn functions.

       Command-line Arguments

       The  argvs  array parameter to MPI_Comm_spawn_multiple should not contain the program name
       since it is given in the first parameter.  The command line that is passed  to  the  newly
       launched  program  will be the program name followed by the strings in corresponding entry
       in the argvs array.

       The IMPI standard only supports MPI-1 functions.  Hence, this function  is  currently  not
       designed to operate within an IMPI job.

       If  an  error occurs in an MPI function, the current MPI error handler is called to handle
       it.  By default, this error handler aborts the MPI job.	The error handler may be  changed
       with  MPI_Errhandler_set  ;  the predefined error handler MPI_ERRORS_RETURN may be used to
       cause error values to be returned (in C and Fortran; this error handler is less useful  in
       with  the  C++  MPI  bindings.	The predefined error handler MPI::ERRORS_THROW_EXCEPTIONS
       should be used in C++ if the error value needs to be recovered).  Note that MPI	does  not
       guarantee that an MPI program can continue past an error.

       All  MPI  routines  (except MPI_Wtime and MPI_Wtick ) return an error value; C routines as
       the value of the function and Fortran routines in the last argument.  The C++ bindings for
       MPI  do not return error values; instead, error values are communicated by throwing excep-
       tions of type MPI::Exception (but not by default).  Exceptions  are  only  thrown  if  the
       error value is not MPI::SUCCESS

       Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI functions will return
       upon an error, there will be no way to recover what the actual error value was.
	      - No error; MPI routine completed successfully.
	      - Invalid communicator.  A common error is to use a null	communicator  in  a  call
	      (not even allowed in MPI_Comm_rank ).
	      -  Spawn	error;	one or more of the applications attempting to be launched failed.
	      Check the returned error code array.
	      - Invalid argument.  Some argument is invalid and is not identified by  a  specific
	      error class.  This is typically a NULL pointer or other such error.
	      -  Invalid  root.  The root must be specified as a rank in the communicator.  Ranks
	      must be between zero and the size of the communicator minus one.
	      - Other error; use MPI_Error_string to get more information about this error code.
	      - An internal error has been detected.  This is fatal.  Please send a bug report to
	      the LAM mailing list (see http://www.lam-mpi.org/contact.php ).

       appschema(5),	bhost(5),    lamboot(1),    MPI_Comm_get_parent(3),    MPI_Comm_merge(3),
       MPI_Comm_spawn_multiple(3),   MPI_Info_create(3),   MPI_Info_set(3),   MPI_Info_delete(3),
       MPI_Info_free(3), MPI_Init(3), mpirun(1)

       For  more information, please see the official MPI Forum web site, which contains the text
       of both the MPI-1 and MPI-2 standards.  These documents contain detailed information about
       each MPI function (most of which is not duplicated in these man pages).


       The  LAM  Team  would  like the thank the MPICH Team for the handy program to generate man
       pages ("doctext" from ftp://ftp.mcs.anl.gov/pub/sowing/sowing.tar.gz ), the  initial  for-
       matting, and some initial text for most of the MPI-1 man pages.


LAM/MPI 6.5.8				    11/10/2002		       MPI_Comm_spawn_multiple(3)

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