MPI_Cancel(3) LAM/MPI MPI_Cancel(3)
MPI_Cancel - Cancels a communication request
int MPI_Cancel(MPI_Request *preq)
preq - communication request (handle)
Cancel has only been implemented for receive requests; it is a no-op for send requests.
The primary expected use of MPI_Cancel is in multi-buffering schemes, where speculative
MPI_Irecv calls are made. When the computation completes, some of these receive requests
may remain; using MPI_Cancel allows the user to cancel these unsatisfied requests.
Cancelling a send operation is much more difficult, in large part because the send will
usually be at least partially complete (the information on the tag, size, and source are
usually sent immediately to the destination). As such, LAM/MPI has not implemented the
canceling of send operations.
The MPI 1.1 specification, in the section on opaque objects, explicitly disallows freeing
a null communicator. The text from the standard is
"A null handle argument is an erroneous IN argument in MPI calls,
unless an exception is explicitly stated in the text that defines the
function. Such exception is allowed for handles to request objects in
Wait and Test calls (sections Communication Completion and Multiple
Completions ). Otherwise, a null handle can only be passed to a
function that allocates a new object and returns a reference to it in
NOTES FOR FORTRAN
All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argu-
ment ierr at the end of the argument list. ierr is an integer and has the same meaning as
the return value of the routine in C. In Fortran, MPI routines are subroutines, and are
invoked with the call statement.
All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran.
If an error occurs in an MPI function, the current MPI error handler is called to handle
it. By default, this error handler aborts the MPI job. The error handler may be changed
with MPI_Errhandler_set ; the predefined error handler MPI_ERRORS_RETURN may be used to
cause error values to be returned (in C and Fortran; this error handler is less useful in
with the C++ MPI bindings. The predefined error handler MPI::ERRORS_THROW_EXCEPTIONS
should be used in C++ if the error value needs to be recovered). Note that MPI does not
guarantee that an MPI program can continue past an error.
All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error value; C routines as
the value of the function and Fortran routines in the last argument. The C++ bindings for
MPI do not return error values; instead, error values are communicated by throwing excep-
tions of type MPI::Exception (but not by default). Exceptions are only thrown if the
error value is not MPI::SUCCESS
Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI functions will return
upon an error, there will be no way to recover what the actual error value was.
- No error; MPI routine completed successfully.
- Invalid MPI_Request ; either null or, MPI_REQUEST_NULL , in the case of a
MPI_Start or MPI_Startall , not a persistent request.
- Invalid argument. Some argument is invalid and is not identified by a specific
error class. This is typically a NULL pointer or other such error.
For more information, please see the official MPI Forum web site, which contains the text
of both the MPI-1 and MPI-2 standards. These documents contain detailed information about
each MPI function (most of which is not duplicated in these man pages).
The LAM Team would like the thank the MPICH Team for the handy program to generate man
pages ("doctext" from ftp://ftp.mcs.anl.gov/pub/sowing/sowing.tar.gz ), the initial for-
matting, and some initial text for most of the MPI-1 man pages.
LAM/MPI 6.5.8 11/10/2002 MPI_Cancel(3)