|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
<HTML>
|
|
Packit Service |
c5cf8c |
<HEAD>
|
|
Packit Service |
c5cf8c |
<META NAME="GENERATOR" CONTENT="DOCTEXT">
|
|
Packit Service |
c5cf8c |
<TITLE>MPI_Cancel</TITLE>
|
|
Packit Service |
c5cf8c |
</HEAD>
|
|
Packit Service |
c5cf8c |
<BODY BGCOLOR="FFFFFF">
|
|
Packit Service |
c5cf8c |
MPI_Cancel
|
|
Packit Service |
c5cf8c |
Cancels a communication request
|
|
Packit Service |
c5cf8c |
Synopsis
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
int MPI_Cancel(MPI_Request * request)
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
Input Parameters
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
request communication request (handle)
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
Notes
|
|
Packit Service |
c5cf8c |
The primary expected use of <tt>MPI_Cancel</tt> is in multi-buffering
|
|
Packit Service |
c5cf8c |
schemes, where speculative <tt>MPI_Irecvs</tt> are made. When the computation
|
|
Packit Service |
c5cf8c |
completes, some of these receive requests may remain; using <tt>MPI_Cancel</tt> allows
|
|
Packit Service |
c5cf8c |
the user to cancel these unsatisfied requests.
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
Cancelling a send operation is much more difficult, in large part because the
|
|
Packit Service |
c5cf8c |
send will usually be at least partially complete (the information on the tag,
|
|
Packit Service |
c5cf8c |
size, and source are usually sent immediately to the destination).
|
|
Packit Service |
c5cf8c |
Users are
|
|
Packit Service |
c5cf8c |
advised that cancelling a send, while a local operation (as defined by the MPI
|
|
Packit Service |
c5cf8c |
standard), is likely to be expensive (usually generating one or more internal
|
|
Packit Service |
c5cf8c |
messages).
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
Thread and Interrupt Safety
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
This routine is thread-safe. This means that this routine may be
|
|
Packit Service |
c5cf8c |
safely used by multiple threads without the need for any user-provided
|
|
Packit Service |
c5cf8c |
thread locks. However, the routine is not interrupt safe. Typically,
|
|
Packit Service |
c5cf8c |
this is due to the use of memory allocation routines such as <tt>malloc
|
|
Packit Service |
c5cf8c |
</tt>or other non-MPICH runtime routines that are themselves not interrupt-safe.
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
Notes for Fortran
|
|
Packit Service |
c5cf8c |
All MPI routines in Fortran (except for <tt>MPI_WTIME</tt> and <tt>MPI_WTICK</tt>) have
|
|
Packit Service |
c5cf8c |
an additional argument <tt>ierr</tt> at the end of the argument list. <tt>ierr
|
|
Packit Service |
c5cf8c |
</tt>is an integer and has the same meaning as the return value of the routine
|
|
Packit Service |
c5cf8c |
in C. In Fortran, MPI routines are subroutines, and are invoked with the
|
|
Packit Service |
c5cf8c |
<tt>call</tt> statement.
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
All MPI objects (e.g., <tt>MPI_Datatype</tt>, <tt>MPI_Comm</tt>) are of type <tt>INTEGER
|
|
Packit Service |
c5cf8c |
</tt>in Fortran.
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
Null Handles
|
|
Packit Service |
c5cf8c |
The MPI 1.1 specification, in the section on opaque objects, explicitly
|
|
Packit Service |
c5cf8c |
disallows freeing a null communicator. The text from the standard is:
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
A null handle argument is an erroneous IN argument in MPI calls, unless an
|
|
Packit Service |
c5cf8c |
exception is explicitly stated in the text that defines the function. Such
|
|
Packit Service |
c5cf8c |
exception is allowed for handles to request objects in Wait and Test calls
|
|
Packit Service |
c5cf8c |
(sections Communication Completion and Multiple Completions ). Otherwise, a
|
|
Packit Service |
c5cf8c |
null handle can only be passed to a function that allocates a new object and
|
|
Packit Service |
c5cf8c |
returns a reference to it in the handle.
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
Errors
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
All MPI routines (except <tt>MPI_Wtime</tt> and <tt>MPI_Wtick</tt>) return an error value;
|
|
Packit Service |
c5cf8c |
C routines as the value of the function and Fortran routines in the last
|
|
Packit Service |
c5cf8c |
argument. Before the value is returned, the current MPI error handler is
|
|
Packit Service |
c5cf8c |
called. By default, this error handler aborts the MPI job. The error handler
|
|
Packit Service |
c5cf8c |
may be changed with <tt>MPI_Comm_set_errhandler</tt> (for communicators),
|
|
Packit Service |
c5cf8c |
<tt>MPI_File_set_errhandler</tt> (for files), and <tt>MPI_Win_set_errhandler</tt> (for
|
|
Packit Service |
c5cf8c |
RMA windows). The MPI-1 routine <tt>MPI_Errhandler_set</tt> may be used but
|
|
Packit Service |
c5cf8c |
its use is deprecated. The predefined error handler
|
|
Packit Service |
c5cf8c |
<tt>MPI_ERRORS_RETURN</tt> may be used to cause error values to be returned.
|
|
Packit Service |
c5cf8c |
Note that MPI does not guarentee that an MPI program can continue past
|
|
Packit Service |
c5cf8c |
an error; however, MPI implementations will attempt to continue whenever
|
|
Packit Service |
c5cf8c |
possible.
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
MPI_SUCCESS No error; MPI routine completed successfully.
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
MPI_ERR_REQUEST Invalid <tt>MPI_Request</tt>. Either null or, in the case of a
|
|
Packit Service |
c5cf8c |
<tt>MPI_Start</tt> or <tt>MPI_Startall</tt>, not a persistent request.
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
MPI_ERR_ARG Invalid argument. Some argument is invalid and is not
|
|
Packit Service |
c5cf8c |
identified by a specific error class (e.g., <tt>MPI_ERR_RANK</tt>).
|
|
Packit Service |
c5cf8c |
|
|
Packit Service |
c5cf8c |
</BODY></HTML>
|