239 lines
7.4 KiB
Groff
239 lines
7.4 KiB
Groff
.\" Man page generated from reStructuredText.
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.TH "MPI_WAIT" "3" "Feb 14, 2025" "" "Open MPI"
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..
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.sp
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\fI\%MPI_Wait\fP — Waits for an MPI send or receive to complete.
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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_Wait(MPI_Request *request, MPI_Status *status)
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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_WAIT(REQUEST, STATUS, IERROR)
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INTEGER REQUEST, STATUS(MPI_STATUS_SIZE), 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_Wait(request, status, ierror)
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TYPE(MPI_Request), INTENT(INOUT) :: request
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TYPE(MPI_Status) :: status
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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 PARAMETER
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.INDENT 0.0
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.IP \(bu 2
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\fBrequest\fP: Request (handle).
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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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\fBstatus\fP: Status object (status).
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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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A call to \fI\%MPI_Wait\fP returns when the operation identified by request is
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complete. If the communication object associated with this request was
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created by a nonblocking send or receive call, then the object is
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deallocated by the call to \fI\%MPI_Wait\fP and the request handle is set to
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\fBMPI_REQUEST_NULL\fP\&.
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.sp
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The call returns, in status, information on the completed
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operation. The content of the status object for a receive operation
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can be accessed as described in the “Return Status” subsection of the
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“Point\-to\-Point Communication” chapter in the \fI\%MPI Standard\fP\&. The status object for a send
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operation may be queried by a call to \fI\%MPI_Test_cancelled\fP (see
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the “Probe and Cancel” section in the \fI\%MPI Standard\fP).
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.sp
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If your application does not need to examine the \fIstatus\fP field, you can
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save resources by using the predefined constant \fBMPI_STATUS_IGNORE\fP as a
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special value for the \fIstatus\fP argument.
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.sp
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One is allowed to call \fI\%MPI_Wait\fP with a null or inactive request
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argument. In this case the operation returns immediately with empty
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status.
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.SH NOTES
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.sp
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Successful return of \fI\%MPI_Wait\fP after an \fI\%MPI_Ibsend\fP implies that the user
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send buffer can be reused i.e., data has been sent out or copied into a
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buffer attached with \fI\%MPI_Buffer_attach\fP\&. Note that, at this point, we can
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no longer cancel the send (for more information, see the “Probe and
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Cancel” section in the \fI\%MPI Standard\fP). If a matching receive is never
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posted, then the buffer cannot be freed. This runs somewhat counter to
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the stated goal of \fI\%MPI_Cancel\fP (always being able to free program space
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that was committed to the communication subsystem).
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.sp
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Example: Simple usage of nonblocking operations and \fI\%MPI_Wait\fP\&.
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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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CALL MPI_COMM_RANK(comm, rank, ierr)
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IF(rank == 0) THEN
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CALL MPI_ISEND(a(1), 10, MPI_REAL, 1, tag, comm, request, ierr)
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**** do some computation ****
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CALL MPI_WAIT(request, status, ierr)
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ELSE IF (rank == 1) THEN
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CALL MPI_IRECV(a(1), 15, MPI_REAL, 0, tag, comm, request, ierr)
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**** do some computation ****
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CALL MPI_WAIT(request, status, ierr)
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END IF
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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 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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Note that per the “Return Status” section in the “Point\-to\-Point
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Communication” chapter in the \fI\%MPI Standard\fP, MPI errors on requests passed to
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\fI\%MPI_Wait\fP do not set the \fBstatus.MPI_ERROR\fP field in the
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returned \fIstatus\fP\&. The error code is always passed to the back\-end
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error handler and may be passed back to the caller through the return
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value of \fI\%MPI_Wait\fP if the back\-end error handler returns it. The
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pre\-defined MPI error handler \fBMPI_ERRORS_RETURN\fP exhibits this
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behavior, for example.
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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_Comm_set_errhandler\fP
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.IP \(bu 2
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\fI\%MPI_File_set_errhandler\fP
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.IP \(bu 2
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\fI\%MPI_Test\fP
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.IP \(bu 2
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\fI\%MPI_Testall\fP
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.IP \(bu 2
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\fI\%MPI_Testany\fP
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.IP \(bu 2
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\fI\%MPI_Testsome\fP
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.IP \(bu 2
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\fI\%MPI_Waitall\fP
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.IP \(bu 2
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\fI\%MPI_Waitany\fP
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.IP \(bu 2
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\fI\%MPI_Waitsome\fP
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.IP \(bu 2
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\fI\%MPI_Win_set_errhandler\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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