260 lines
7.8 KiB
Groff
260 lines
7.8 KiB
Groff
.\" Man page generated from reStructuredText.
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.TH "MPI_INIT_THREAD" "3" "Feb 14, 2025" "" "Open MPI"
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..
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.sp
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\fI\%MPI_Init_thread\fP — Initializes the MPI execution environment
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.SH SYNTAX
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.SS C Syntax
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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#include <mpi.h>
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int MPI_Init_thread(int *argc, char ***argv,
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int required, int *provided)
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SS Fortran Syntax
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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USE MPI
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! or the older form: INCLUDE \(aqmpif.h\(aq
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MPI_INIT_THREAD(REQUIRED, PROVIDED, IERROR)
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INTEGER REQUIRED, PROVIDED, IERROR
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SS Fortran 2008 Syntax
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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USE mpi_f08
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MPI_Init_thread(required, provided, ierror)
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INTEGER, INTENT(IN) :: required
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INTEGER, INTENT(OUT) :: provided
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INTEGER, OPTIONAL, INTENT(OUT) :: ierror
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SH INPUT PARAMETERS
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.INDENT 0.0
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.IP \(bu 2
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\fBargc\fP: C only: Pointer to the number of arguments.
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.IP \(bu 2
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\fBargv\fP: C only: Argument vector.
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.IP \(bu 2
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\fBrequired\fP: Desired level of thread support (integer).
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.UNINDENT
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.SH OUTPUT PARAMETERS
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.INDENT 0.0
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.IP \(bu 2
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\fBprovided\fP: Available level of thread support (integer).
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.IP \(bu 2
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\fBierror\fP: Fortran only: Error status (integer).
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.UNINDENT
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.SH DESCRIPTION
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.sp
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This routine, or \fI\%MPI_Init\fP, must be called before most other MPI routines
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are called. There are a small number of exceptions, such as
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\fI\%MPI_Initialized\fP and \fI\%MPI_Finalized\fP\&. MPI can be initialized at most once;
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subsequent calls to \fI\%MPI_Init\fP or \fI\%MPI_Init_thread\fP are erroneous.
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.sp
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\fI\%MPI_Init_thread\fP, as compared to \fI\%MPI_Init\fP, has a provision to request a
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certain level of thread support in \fIrequired\fP:
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.INDENT 0.0
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.TP
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.B MPI_THREAD_SINGLE
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Only one thread will execute.
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.TP
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.B MPI_THREAD_FUNNELED
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If the process is multithreaded, only the thread that called
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\fI\%MPI_Init_thread\fP will make MPI calls.
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.TP
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.B MPI_THREAD_SERIALIZED
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If the process is multithreaded, only one thread will make MPI
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library calls at one time.
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.TP
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.B MPI_THREAD_MULTIPLE
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If the process is multithreaded, multiple threads may call MPI at
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once with no restrictions.
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.UNINDENT
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.sp
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The level of thread support available to the program is set in
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\fIprovided\fP\&. In Open MPI, the value is dependent on how the library was
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configured and built. Note that there is no guarantee that \fIprovided\fP
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will be greater than or equal to \fIrequired\fP\&.
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.sp
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Also note that calling \fI\%MPI_Init_thread\fP with a \fIrequired\fP value of
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MPI_THREAD_SINGLE is equivalent to calling \fI\%MPI_Init\fP\&.
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.sp
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All MPI programs must contain a call to \fI\%MPI_Init\fP or \fI\%MPI_Init_thread\fP\&.
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Open MPI accepts the C \fIargc\fP and \fIargv\fP arguments to main, but neither
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modifies, interprets, nor distributes them:
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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/* declare variables */
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MPI_Init_thread(&argc, &argv, req, &prov);
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/* parse arguments */
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/* main program */
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MPI_Finalize();
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.SH NOTES
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.sp
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The Fortran version does not have provisions for \fBargc\fP and \fBargv\fP and
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takes only \fBIERROR\fP\&.
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.sp
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It is the caller’s responsibility to check the value of \fBprovided\fP, as
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it may be less than what was requested in \fBrequired\fP\&.
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.sp
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The MPI Standard does not say what a program can do before an
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\fI\%MPI_Init_thread\fP or after an \fI\%MPI_Finalize\fP\&. In the Open MPI
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implementation, it should do as little as possible. In particular, avoid
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anything that changes the external state of the program, such as opening
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files, reading standard input, or writing to standard output.
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.SS MPI_THREAD_MULTIPLE Support
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.sp
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\fBMPI_THREAD_MULTIPLE\fP support is included if the environment in which
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Open MPI was built supports threading. You can check the output of
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\fI\%ompi_info(1)\fP to see if Open MPI has
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\fBMPI_THREAD_MULTIPLE\fP support:
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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shell$ ompi_info | grep "Thread support"
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Thread support: posix (MPI_THREAD_MULTIPLE: yes, OPAL support: yes, OMPI progress: no, Event lib: yes)
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shell$
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.sp
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The \fBMPI_THREAD_MULTIPLE: yes\fP portion of the above output indicates
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that Open MPI was compiled with \fBMPI_THREAD_MULTIPLE\fP support.
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.sp
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Note that there is a small performance penalty for using
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\fBMPI_THREAD_MULTIPLE\fP support; latencies for short messages will be higher
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as compared to when using \fBMPI_THREAD_SINGLE\fP, for example.
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.SH ERRORS
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.sp
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Almost all MPI routines return an error value; C routines as the return result
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of the function and Fortran routines in the last argument.
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.sp
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Before the error value is returned, the current MPI error handler associated
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with the communication object (e.g., communicator, window, file) is called.
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If no communication object is associated with the MPI call, then the call is
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considered attached to MPI_COMM_SELF and will call the associated MPI error
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handler. When MPI_COMM_SELF is not initialized (i.e., before
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\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
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Model exclusively) the error raises the initial error handler. The initial
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error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
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MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
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argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
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If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
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error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error
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handler is called for all other MPI functions.
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.sp
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Open MPI includes three predefined error handlers that can be used:
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.INDENT 0.0
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.IP \(bu 2
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\fBMPI_ERRORS_ARE_FATAL\fP
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Causes the program to abort all connected MPI processes.
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.IP \(bu 2
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\fBMPI_ERRORS_ABORT\fP
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An error handler that can be invoked on a communicator,
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window, file, or session. When called on a communicator, it
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acts as if \fI\%MPI_Abort\fP was called on that communicator. If
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called on a window or file, acts as if \fI\%MPI_Abort\fP was called
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on a communicator containing the group of processes in the
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corresponding window or file. If called on a session,
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aborts only the local process.
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.IP \(bu 2
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\fBMPI_ERRORS_RETURN\fP
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Returns an error code to the application.
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.UNINDENT
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.sp
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MPI applications can also implement their own error handlers by calling:
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.INDENT 0.0
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.IP \(bu 2
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\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
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.IP \(bu 2
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\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
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.IP \(bu 2
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\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
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.IP \(bu 2
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\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
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.UNINDENT
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.sp
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Note that MPI does not guarantee that an MPI program can continue past
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an error.
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.sp
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See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
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.sp
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See the Error Handling section of the MPI\-3.1 standard for
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more information.
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.sp
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\fBSEE ALSO:\fP
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.INDENT 0.0
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.INDENT 3.5
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.INDENT 0.0
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.IP \(bu 2
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\fI\%MPI_Init\fP
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.IP \(bu 2
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\fI\%MPI_Initialized\fP
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.IP \(bu 2
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\fI\%MPI_Finalize\fP
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.IP \(bu 2
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\fI\%MPI_Finalized\fP
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.UNINDENT
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.UNINDENT
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.UNINDENT
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.SH COPYRIGHT
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2003-2025, The Open MPI Community
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.\" Generated by docutils manpage writer.
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.
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