MPI_Init_thread(3) Open MPI MPI_Init_thread(3)NAMEMPI_Init_thread - Initializes the MPI execution environment
SYNTAXC Syntax
#include <mpi.h>
int MPI_Init_thread(int *argc, char ***argv,
int required, int *provided)
Fortran Syntax
INCLUDE 'mpif.h'
MPI_INIT_THREAD(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 restric‐
tions.
The level of thread support available to the program is set in pro‐
vided, 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.
Also note that calling MPI_Init_thread with a required value of
MPI_THREAD_SINGLE is equivalent to calling MPI_Init.
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 implementa‐
tion, 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.
MPI_THREAD_MULTIPLE Support
MPI_THREAD_MULTIPLE support is included if Open MPI was configured with
the --enable-mpi-thread-multiple configure switch. You can check the
output of ompi_info(1) to see if Open MPI has MPI_THREAD_MULTIPLE sup‐
port:
shell$ ompi_info | grep -i thread
Thread support: posix (mpi: yes, progress: no)
shell$
The "mpi: yes" portion of the above output indicates that Open MPI was
compiled with MPI_THREAD_MULTIPLE support.
Note that MPI_THREAD_MULTIPLE support is only lightly tested. It
likely does not work for thread-intensive applications. Also note that
only the MPI point-to-point communication functions for the BTL's
listed below are considered thread safe. Other support functions
(e.g., MPI attributes) have not been certified as safe when simultane‐
ously used by multiple threads.
tcp
sm
mx
elan
self
Note that Open MPI's thread support is in a fairly early stage; the
above devices are likely to work, but the latency is likely to be
fairly high. Specifically, efforts so far have concentrated on cor‐
rectness, not performance (yet).
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++ func‐
tions 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
1.7.4 Feb 04, 2014 MPI_Init_thread(3)
