MPI_Init_thread(3OpenMPI) MPI_Init_thread(3OpenMPI)
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 sup-port support
port 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_Final-ize. MPI_Finalize.
ize. In the Open MPI implementation, it should do as little as possible. In particular, avoid any-thing anything
thing 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
Open MPI 1.2 September 2006 MPI_Init_thread(3OpenMPI)
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