NAME¶
MPI_Cancel - Cancels a communication request
SYNOPSIS¶
int MPI_Cancel(MPI_Request *request)
- request
- - communication request (handle)
NOTES¶
The primary expected use of
MPI_Cancel is in multi-buffering schemes,
where speculative
MPI_Irecvs 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). Users are
advised that cancelling a send, while a local operation (as defined by the MPI
standard), is likely to be expensive (usually generating one or more internal
messages).
THREAD AND INTERRUPT SAFETY¶
This routine is thread-safe. This means that this routine may be safely used by
multiple threads without the need for any user-provided thread locks. However,
the routine is not interrupt safe. Typically, this is due to the use of memory
allocation routines such as
malloc or other non-MPICH runtime routines
that are themselves not interrupt-safe.
NOTES FOR FORTRAN¶
All MPI routines in Fortran (except for
MPI_WTIME and
MPI_WTICK )
have an additional argument
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.
NULL HANDLES¶
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 the handle.
ERRORS¶
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. Before the value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job. The error handler
may be changed with
MPI_Comm_set_errhandler (for communicators),
MPI_File_set_errhandler (for files), and
MPI_Win_set_errhandler
(for RMA windows). The MPI-1 routine
MPI_Errhandler_set may be used but
its use is deprecated. The predefined error handler
MPI_ERRORS_RETURN
may be used to cause error values to be returned. Note that MPI does
not guarentee that an MPI program can continue past an error; however,
MPI implementations will attempt to continue whenever possible.
- MPI_SUCCESS
- - No error; MPI routine completed successfully.
- MPI_ERR_REQUEST
- - Invalid MPI_Request . Either null or, in the case of a
MPI_Start or MPI_Startall , not a persistent request.
- MPI_ERR_ARG
- - Invalid argument. Some argument is invalid and is not identified by a
specific error class (e.g., MPI_ERR_RANK ).
LOCATION¶
/tmp/gyCYfBi4J6/mpich-3.1/src/mpi/pt2pt/cancel.c