MPI_INIT, MPI_Init

Purpose

Initializes MPI.

C synopsis

#include <mpi.h>
int MPI_Init(int *argc,char ***argv);

C++ synopsis

#include mpi.h
void MPI::Init(int& argc, char**& argv);

#include mpi.h
void MPI::Init();

FORTRAN synopsis

include 'mpif.h' or use mpi
MPI_INIT(INTEGER IERROR)

Parameters

IERROR
     is the FORTRAN return code. It is always the last argument.

Description

This subroutine initializes MPI. All MPI programs must call MPI_INIT before
any other MPI routine (with the exception of MPI_INITIALIZED). More than
one call to MPI_INIT by any task is erroneous.

Notes

For either MPI_INIT or MPI_INIT_THREAD, PE MPI normally returns support
that is equivalent to MPI_THREAD_MULTIPLE. For more information, see
MPI_INIT_THREAD.

argc and argv are the arguments passed to main. PE MPI does not examine or
modify these arguments when they are passed to MPI_INIT. In accordance with
MPI-2, it is valid to pass NULL in place of argc and argv.

In a threads environment, MPI_INIT needs to be called once per task and not
once per thread. You don't need to call it on the main thread but both
MPI_INIT and MPI_FINALIZE must be called on the same thread.

MPI_INIT opens a local socket and binds it to a port, sends that
information to POE, receives a list of destination addresses and ports,
opens a socket to send to each one, verifies that communication can be
established, and distributes MPI internal state to each task.

In the signal-handling library, this work is done in the initialization
stub added by POE, so that the library is open when your main program is
called. MPI_INIT sets a flag saying that you called it.

In the threads library, the work of MPI_INIT is done when the function is
called. The local socket is not open when your main program starts. This
may affect the numbering of file descriptors, the use of the environment
strings, and the treatment of stdin (the MP_HOLD_STDIN variable). If an
existing non-threads program is relinked using the threads library, the
code prior to calling MPI_INIT should be examined with these thoughts in
mind.

Also for the threads library, if you had registered a function as an AIX
signal handler for the SIGIO signal at the time that MPI_INIT was called,
that function will be added to the interrupt service thread and be
processed as a thread function rather than as a signal handler. You'll need
to set the environment variable MP_CSS_INTERRUPT=YES to get arriving
packets to invoke the interrupt service thread.

Related information

     MPI_FINALIZE
     MPI_INITIALIZED