210 lines
7.0 KiB
Groff
210 lines
7.0 KiB
Groff
.\" Man page generated from reStructuredText.
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.TH "MPI_CANCEL" "3" "Feb 14, 2025" "" "Open MPI"
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.sp
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\fI\%MPI_Cancel\fP — Cancels a communication request.
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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_Cancel(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_CANCEL(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_Cancel(request, ierror)
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TYPE(MPI_Request), INTENT(IN) :: 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 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 OUTPUT PARAMETER
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.INDENT 0.0
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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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The \fI\%MPI_Cancel\fP operation allows pending communications to be canceled.
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This is required for cleanup. Posting a send or a receive ties up user
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resources (send or receive buffers), and a cancel may be needed to free
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these resources gracefully.
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.sp
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A call to \fI\%MPI_Cancel\fP marks for cancellation a pending, nonblocking
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communication operation (send or receive). The cancel call is local. It
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returns immediately, possibly before the communication is actually
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canceled. It is still necessary to complete a communication that has
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been marked for cancellation, using a call to \fI\%MPI_Request_free\fP,
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\fI\%MPI_Wait\fP, or \fI\%MPI_Test\fP (or any of the derived operations).
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.sp
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If a communication is marked for cancellation, then an \fI\%MPI_Wait\fP call for
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that communication is guaranteed to return, irrespective of the
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activities of other processes (i.e., \fI\%MPI_Wait\fP behaves as a local
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function); similarly if \fI\%MPI_Test\fP is repeatedly called in a busy wait
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loop for a canceled communication, then \fI\%MPI_Test\fP will eventually be
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successful.
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.sp
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\fI\%MPI_Cancel\fP can be used to cancel a communication that uses a persistent
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request (see Section 3.9 in the \fI\%MPI Standard\fP, “Persistent
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Communication Requests”) in the same way it is used for nonpersistent
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requests. A successful cancellation cancels the active communication,
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but not the request itself. After the call to \fI\%MPI_Cancel\fP and the
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subsequent call to \fI\%MPI_Wait\fP or \fI\%MPI_Test\fP, the request becomes inactive
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and can be activated for a new communication.
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.sp
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The successful cancellation of a buffered send frees the buffer space
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occupied by the pending message.
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.sp
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Either the cancellation succeeds or the communication succeeds, but not
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both. If a send is marked for cancellation, then it must be the case
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that either the send completes normally, in which case the message sent
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is received at the destination process, or that the send is successfully
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canceled, in which case no part of the message is received at the
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destination. Then, any matching receive has to be satisfied by another
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send. If a receive is marked for cancellation, then it must be the case
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that either the receive completes normally, or that the receive is
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successfully canceled, in which case no part of the receive buffer is
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altered. Then, any matching send has to be satisfied by another receive.
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.sp
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If the operation has been canceled, then information to that effect will
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be returned in the status argument of the operation that completes the
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communication.
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.SH NOTES
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.sp
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The primary expected use of \fI\%MPI_Cancel\fP is in multi\-buffering schemes,
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where speculative MPI_Irecvs are made. When the computation completes,
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some of these requests may remain; using \fI\%MPI_Cancel\fP allows the user to
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cancel these unsatisfied requests.
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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_Probe\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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