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       MPI_Comm_spawn_multiple  -   Spawn  a dynamic MPI process from multiple


       #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
       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 processes.

       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    second    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 intracommunicator (with the  MPI_Intercomm_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_multiple .  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 repeats.

       Process Terminiation

       Note   that   the   process[es]   spawned   by   MPI_COMM_SPAWN    (and
       MPI_COMM_SPAWN_MULTIPLE  )  effectively  become  orphans.  That is, the
       spawnning MPI application does not wait for the spawned application  to
       finish.   Hence,  there  is  no  guarantee  the spawned application has
       finished when the spawning completes.  Similarly, killing the  spawning
       application will also have no effect on the spawned application.

       User  applications  can  effect  this kind of behavior with MPI_BARRIER
       between the spawning and spawned processed before MPI_FINALIZE .

       Note that lamclean will kill *all* MPI processes.

       Process Count

       The maxprocs array parameter to MPI_Comm_spawn_multiple  specifies  the
       exact  number  of  processes  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 integer 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)).

       See  MPI_Init(3) for other pre-defined attributes that are helpful when

       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  exceptions
       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-


       appschema(5),     bhost(5),     lamboot(1),     MPI_Comm_get_parent(3),
       MPI_Intercomm_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),


       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     ),    the    initial
       formatting, and some initial text for most of the MPI-1 man pages.