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.TH getdns_cancel_callback 3 "December 2015" "getdns 1.6.0" 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),