.\" The "BSD-New" License
.\" 
.\" Copyright (c) 2013, NLnet Labs, Verisign, Inc.
.\" All rights reserved.
.\" 
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions are met:
.\" * Redistributions of source code must retain the above copyright
.\"   notice, this list of conditions and the following disclaimer.
.\" * Redistributions in binary form must reproduce the above copyright
.\"   notice, this list of conditions and the following disclaimer in the
.\"   documentation and/or other materials provided with the distribution.
.\" * Neither the names of the copyright holders nor the
.\"   names of its contributors may be used to endorse or promote products
.\"   derived from this software without specific prior written permission.
.\" 
.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
.\" DISCLAIMED. IN NO EVENT SHALL Verisign, Inc. BE LIABLE FOR ANY
.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
.\" SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\" 

.TH getdns_cancel_callback 3 "@date@" "getdns @version@" getdns
.SH NAME
.B getdns_cancel_callback
-- cancel an outstanding asyn getdns request

.SH LIBRARY
DNS Resolver library (libgetdns, \-lgetdns)

.SH SYNOPSIS
#include <getdns.h>

getdns_return_t 
.br
.B getdns_cancel_callback
(getdns_context_t context,
.RS 3
.br
getdns_transaction_t *transaction_id)
.RE

.SH DESCRIPTION

.LP
To cancel an outstanding callback, use getdns_cancel_callback. This causes the
API to call the callback with a callback_type of GETDNS_CALLBACK_CANCEL if the
callback for this transaction_id has not already been called. The callback code
for cancellation should clean up any memory related to the identified call,
such as to deallocate the memory for the userarg. getdns_cancel_callback() may
return immediately, even before the callback finishes its work and returns. 

.HP 3
.I context
see getdns_context (3)

.HP 3
.I transaction_id
populated by the API and used to identify the callback (for example to getdns_cancel_callback), can be NULL, set to 0 if the function fails

.HP
.SH "RETURN VALUES"

Upon successful completion the functions return
.B GETDNS_RETURN_GOOD
, otherwise the following error values are returned:

.LP
.B GETDNS_RETURN_INVALID_PARAMETER
if context == NULL
.LP
.B GETDNS_RETURN_UNKNOWN_TRANSACTION 
if the transaction_id that is unknown or belongs to a callback that has already been called 

.SH EXAMPLES

TBD

.SH FILES
.br
/etc/hosts
.br
/etc/resolv.conf

.SH SEE ALSO
.BR libgetdns (3),
.BR getdns_context (3),
.BR getdns_general (3),
.BR getdns_hostname (3),
.BR getdns_service (3),

