Linux Certif

Toute la documentation sur la certification Linux LPI

MPI_Init_thread

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