249 lines
7.3 KiB
Groff
249 lines
7.3 KiB
Groff
.\" Man page generated from reStructuredText.
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.TH "MPI_REQUEST_FREE" "3" "Feb 14, 2025" "" "Open MPI"
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..
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.sp
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\fI\%MPI_Request_free\fP — Frees a communication request object.
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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_Request_free(MPI_Request *request)
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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_REQUEST_FREE(REQUEST, IERROR)
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INTEGER REQUEST, 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_Request_free(request, ierror)
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TYPE(MPI_Request), INTENT(INOUT) :: request
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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/OUTPUT PARAMETER
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.INDENT 0.0
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.IP \(bu 2
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\fBrequest\fP: Communication request (handle).
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.UNINDENT
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.SH DESCRIPTION
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.sp
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This operation allows a request object to be deallocated without waiting
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for the associated communication to complete.
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.sp
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\fI\%MPI_Request_free\fP marks the request object for deallocation and sets
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request to MPI_REQUEST_NULL. Any ongoing communication that is
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associated with the request will be allowed to complete. The request
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will be deallocated only after its completion.
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.SH NOTES
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.sp
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Once a request is freed by a call to \fI\%MPI_Request_free\fP, it is not
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possible to check for the successful completion of the associated
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communication with calls to \fI\%MPI_Wait\fP or \fI\%MPI_Test\fP\&. Also, if an error
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occurs subsequently during the communication, an error code cannot be
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returned to the user — such an error must be treated as fatal.
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Questions arise as to how one knows when the operations have completed
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when using \fI\%MPI_Request_free\fP\&. Depending on the program logic, there may
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be other ways in which the program knows that certain operations have
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completed and this makes usage of \fI\%MPI_Request_free\fP practical. For
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example, an active send request could be freed when the logic of the
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program is such that the receiver sends a reply to the message sent —
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the arrival of the reply informs the sender that the send has completed
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and the send buffer can be reused. An active receive request should
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never be freed, as the receiver will have no way to verify that the
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receive has completed and the receive buffer can be reused.
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.sp
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\fBExample:\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(MPI_COMM_WORLD, rank)
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IF(rank == 0) THEN
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DO i=1, n
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CALL MPI_ISEND(outval, 1, MPI_REAL, 1, 0, req, ierr)
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CALL MPI_REQUEST_FREE(req, ierr)
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CALL MPI_IRECV(inval, 1, MPI_REAL, 1, 0, req, ierr)
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CALL MPI_WAIT(req, status, ierr)
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END DO
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ELSE IF (rank == 1) THEN
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CALL MPI_IRECV(inval, 1, MPI_REAL, 0, 0, req, ierr)
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CALL MPI_WAIT(req, status)
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DO I=1, n\-1
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CALL MPI_ISEND(outval, 1, MPI_REAL, 0, 0, req, ierr)
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CALL MPI_REQUEST_FREE(req, ierr)
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CALL MPI_IRECV(inval, 1, MPI_REAL, 0, 0, req, ierr)
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CALL MPI_WAIT(req, status, ierr)
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END DO
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CALL MPI_ISEND(outval, 1, MPI_REAL, 0, 0, req, ierr)
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CALL MPI_WAIT(req, status)
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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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.sp
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This routine is normally used to free persistent requests created with
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either \fI\%MPI_Recv_init\fP or \fI\%MPI_Send_init\fP and friends. However, it can
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be used to free a request created with \fI\%MPI_Irecv\fP or \fI\%MPI_Isend\fP and
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friends; in that case the use can not use the test/wait routines on the
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request.
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.sp
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It \fBis\fP permitted to free an active request. However, once freed, you
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can not use the request in a wait or test routine (e.g., \fI\%MPI_Wait\fP ).
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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_Isend\fP
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.IP \(bu 2
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\fI\%MPI_Irecv\fP
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.IP \(bu 2
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\fI\%MPI_Issend\fP
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.IP \(bu 2
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\fI\%MPI_Ibsend\fP
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.IP \(bu 2
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\fI\%MPI_Irsend\fP
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.IP \(bu 2
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\fI\%MPI_Recv_init\fP
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.IP \(bu 2
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\fI\%MPI_Send_init\fP
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.IP \(bu 2
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\fI\%MPI_Ssend_init\fP
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.IP \(bu 2
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\fI\%MPI_Rsend_init\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_Wait\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_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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.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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