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MPI_Cancel(3)			      MPI			 MPI_Cancel(3)

NAME
       MPI_Cancel -  Cancels a communication request

SYNOPSIS
       int MPI_Cancel(MPI_Request *request)

INPUT PARAMETER
       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  be-
       cause  the send will usually be at least	partially complete (the	infor-
       mation 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 com-
       municators),  MPI_File_set_errhandler  (for files), and MPI_Win_set_er-
       rhandler	(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	 when-
       ever 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 identi-
	      fied by a	specific error class (e.g., MPI_ERR_RANK ).

LOCATION
       src/mpi/pt2pt/cancel.c

				   10/3/2012			 MPI_Cancel(3)

NAME | SYNOPSIS | INPUT PARAMETER | NOTES | THREAD AND INTERRUPT SAFETY | NOTES FOR FORTRAN | NULL HANDLES | ERRORS | LOCATION

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