MPI_Init_thread(3)                 Open MPI                 MPI_Init_thread(3)



NAME
       MPI_Init_thread - Initializes the MPI execution environment


SYNTAX
C Syntax
       #include <mpi.h>
       int MPI_Init_thread(int *argc, char ***argv,
            int required, int *provided)


Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_INIT(REQUIRED, PROVIDED, IERROR)
            INTEGER   REQUIRED, PROVIDED, IERROR


C++ Syntax
       #include <mpi.h>
       int MPI::Init_thread(int& argc, char**& argv, int required)
       int MPI::Init_thread(int required)


INPUT PARAMETERS
       argc      C/C++ only: Pointer to the number of arguments.

       argv      C/C++ only: Argument vector.

       required  Desired level of thread support (integer).


OUTPUT PARAMETERS
       provided  Available level of thread support (integer).

       IERROR    Fortran only: Error status (integer).


DESCRIPTION
       This routine, or MPI_Init, must be called before any other MPI routine
       (apart from MPI_Initialized) is called. MPI can be initialized at most
       once; subsequent calls to MPI_Init or MPI_Init_thread are erroneous.

       MPI_Init_thread, as compared to MPI_Init, has a provision to request a
       certain level of thread support in required:

       MPI_THREAD_SINGLE       Only one thread will execute.

       MPI_THREAD_FUNNELED     If the process is multithreaded, only the
                               thread that called MPI_Init_thread will make
                               MPI calls.

       MPI_THREAD_SERIALIZED   If the process is multithreaded, only one
                               thread will make MPI library calls at one time.

       MPI_THREAD_MULTIPLE     If the process is multithreaded, multiple
                               threads may call MPI at once with no
                               restrictions.

The level of thread support available to the program is set in
       provided, except in C++, where it is the return value of the function.
       In Open MPI, the value is dependent on how the library was configured
       and built. Note that there is no guarantee that provided will be
       greater than or equal to required.

       All MPI programs must contain a call to MPI_Init or MPI_Init_thread.
       Open MPI accepts the C/C++ argc and argv arguments to main, but neither
       modifies, interprets, nor distributes them:

            {
                 /* declare variables */
                 MPI_Init_thread(&argc, &argv, req, &prov);
                 /* parse arguments */
                 /* main program */
                 MPI_Finalize();
            }


NOTES
       The Fortran version does not have provisions for argc and argv and
       takes only IERROR.

       It is the caller's responsibility to check the value of provided, as it
       may be less than what was requested in required.

       The MPI Standard does not say what a program can do before an
       MPI_Init_thread or after an MPI_Finalize. In the Open MPI
       implementation, it should do as little as possible. In particular,
       avoid anything that changes the external state of the program, such as
       opening files, reading standard input, or writing to standard output.


ERRORS
       Almost all MPI routines return an error value; C routines as the value
       of the function and Fortran routines in the last argument. C++
       functions do not return errors. If the default error handler is set to
       MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
       will be used to throw an MPI:Exception object.

       Before the error value is returned, the current MPI error handler is
       called. By default, this error handler aborts the MPI job, except for
       I/O function errors. The error handler may be changed with
       MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN
       may be used to cause error values to be returned. Note that MPI does
       not guarantee that an MPI program can continue past an error.


SEE ALSO
       MPI_Init
       MPI_Initialized
       MPI_Finalize




1.4.1                            Jan 14, 2010               MPI_Init_thread(3)
