Re: [Libevent-users] Enable/disable write callback for UDP

[Nick Mathewson <nickm@xxxxxxxxxxxxx>]

On Sat, Apr 20, 2013 at 3:36 PM, Jan Danielsson
<jan.m.danielsson@xxxxxxxxx> wrote:
> Hello,
>
>    I'm doing this (roughly):
>
>    ---------------
>    udp_sock = create_udo4_any_socket("7777");
>    evutil_make_socket_nonblocking(udp_sock);
>    udp_event = event_new(base, udp_sock, EV_READ|EV_WRITE|EV_PERSIST,
>       proc_udp_packet, (void*)base);
>    event_add(udp_event, NULL);
>    ---------------
>
>    But I want to disable, and later re-enable, EV_WRITE in the callback
> function (well, in other functions as well, but I'm guessing the method
> would be the same regardless). How is this done?

The easiest approach is to construct two separate events: one with
EV_WRITE and one with EV_READ, and then use event_del() to disable the
write event and event_add() to re-enable it again.

You can also use event_assign() to change the setup of the event,
replacing EV_READ|EV_WRITE with EV_READ, but you need to be careful:
it is illegal (and will cause undefined behavior) to call
event_assign() on a currently pending or active event.  So you would
need to event_del() the event, event_assign() it, and event_add() it
again.

There are probably other good approaches too.

best wishes,
-- 
Nick
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