# MPI_Comm_spawn

Spawn up to maxprocs instances of a single MPI application

## Synopsis

    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[])

## Input Parameters

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)

## Output Parameters

intercomm
  intercommunicator between original group and the newly spawned group (handle)
array_of_errcodes
  one code per process (array of integer)

## Thread and Interrupt Safety

This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as `malloc` or other non-MPICH runtime routines that are themselves not interrupt-safe.

## Notes for Fortran

All MPI routines in Fortran (except for `MPI_WTIME` and `MPI_WTICK`) have an additional argument `ierr` at the end of the argument list. `ierr` is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the `call` statement.

All MPI objects (e.g., `MPI_Datatype`, `MPI_Comm`) are of type `INTEGER` in Fortran.

## Errors

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. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with `MPI_Comm_set_errhandler` (for communicators), `MPI_File_set_errhandler` (for files), and `MPI_Win_set_errhandler` (for RMA windows). The MPI-1 routine `MPI_Errhandler_set` may be used but its use is deprecated. The predefined error handler `MPI_ERRORS_RETURN` may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

MPI_SUCCESS
  No error; MPI routine completed successfully.

MPI_ERR_COMM
  Invalid communicator. A common error is to use a null communicator in a call (not even allowed in `MPI_Comm_rank`).

MPI_ERR_ARG
  Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., `MPI_ERR_RANK`).

MPI_ERR_INFO
  Invalid Info

MPI_ERR_SPAWN

Location:comm_spawn.c