1MPI_Cancel(3) LAM/MPI MPI_Cancel(3)
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6 MPI_Cancel - Cancels a communication request
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9 #include <mpi.h>
10 int MPI_Cancel(MPI_Request *preq)
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13 preq - communication request (handle)
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17 Cancel has only been implemented for receive requests; it is a no-op
18 for send requests. The primary expected use of MPI_Cancel is in multi-
19 buffering schemes, where speculative MPI_Irecv calls are made. When
20 the computation completes, some of these receive requests may remain;
21 using MPI_Cancel allows the user to cancel these unsatisfied requests.
22 Cancelling a send operation is much more difficult, in large part
24 because the send will usually be at least partially complete (the
25 information on the tag, size, and source are usually sent immediately
26 to the destination). As such, LAM/MPI has not implemented the cancel‐
27 ing of send operations.
28
31 The MPI 1.1 specification, in the section on opaque objects, explicitly
32 disallows freeing a null communicator. The text from the standard is
33 "A null handle argument is an erroneous IN argument in MPI calls,
35 unless an exception is explicitly stated in the text that defines the
36 function. Such exception is allowed for handles to request objects in
37 Wait and Test calls (sections Communication Completion and Multiple
38 Completions ). Otherwise, a null handle can only be passed to a
39 function that allocates a new object and returns a reference to it in
40 the handle."
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45 All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have
46 an additional argument ierr at the end of the argument list. ierr is
47 an integer and has the same meaning as the return value of the routine
48 in C. In Fortran, MPI routines are subroutines, and are invoked with
49 the call statement.
50 All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in
52 Fortran.
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56 If an error occurs in an MPI function, the current MPI error handler is
57 called to handle it. By default, this error handler aborts the MPI
58 job. The error handler may be changed with MPI_Errhandler_set ; the
59 predefined error handler MPI_ERRORS_RETURN may be used to cause error
60 values to be returned (in C and Fortran; this error handler is less
61 useful in with the C++ MPI bindings. The predefined error handler
62 MPI::ERRORS_THROW_EXCEPTIONS should be used in C++ if the error value
63 needs to be recovered). Note that MPI does not guarantee that an MPI
64 program can continue past an error.
65 All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error
67 value; C routines as the value of the function and Fortran routines in
68 the last argument. The C++ bindings for MPI do not return error val‐
69 ues; instead, error values are communicated by throwing exceptions of
70 type MPI::Exception (but not by default). Exceptions are only thrown
71 if the error value is not MPI::SUCCESS .
72 Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI
75 functions will return upon an error, there will be no way to recover
76 what the actual error value was.
77 MPI_SUCCESS
78 - No error; MPI routine completed successfully.
79 MPI_ERR_REQUEST
80 - Invalid MPI_Request ; either null or, MPI_REQUEST_NULL , in
81 the case of a MPI_Start or MPI_Startall , not a persistent
82 request.
83 MPI_ERR_ARG
84 - Invalid argument. Some argument is invalid and is not identi‐
85 fied by a specific error class. This is typically a NULL
86 pointer or other such error.
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90 For more information, please see the official MPI Forum web site, which
91 contains the text of both the MPI-1 and MPI-2 standards. These docu‐
92 ments contain detailed information about each MPI function (most of
93 which is not duplicated in these man pages).
94 http://www.mpi-forum.org/
96
100 The LAM Team would like the thank the MPICH Team for the handy program
101 to generate man pages ("doctext" from ftp://ftp.mcs.anl.gov/pub/sow‐
102 ing/sowing.tar.gz ), the initial formatting, and some initial text for
103 most of the MPI-1 man pages.
104
106 cancel.c
107LAM/MPI 7.1.2 2/23/2006 MPI_Cancel(3)