Re: [Libevent-users] silly question: 1.x to 2.x event_add behavior

[Nick Mathewson <nickm@xxxxxxxxxxxxx>]

On Wed, Apr 30, 2014 at 8:24 AM, Denis Hainsworth
<denis@xxxxxxxxxxxxxxxxxxx> wrote:
> I have question I'm hoping will short-cut an investigation I'm doing
> into some inherited code.  Essentially we have some real simple code
> which sets up an event with a timer and depending on certain things
> changes the timer during each loop.  We are seeing a difference in
> behavior from when it was using 1.x libevent and 2.x.
>
> We call event_set at the start of the code for 60 seconds, and then
> during each loop use event_add to set the timer to however many  seconds
> from current time to get to the next minute.  Its pretty dumb code and
> there are lots of things wrong with it but it has been working.

I think you might be mixing something up here; event_set() doesn't set
timeouts; that's in event_add().

event_add(), on the other hand, doesn't change callbacks.

It's not supported to call event_set() on an event that is currently
pending, and it wasn't supported in Libevent 1.x either -- most
programs that do that will get mysterious crashes as the internal data
structures get corrupted.  It's like using free()d memory -- some
programs will get away with it, and some programs won't, but it's a
bug either way.

If you need to call event_set() on an event that might be pending, you
need to call event_del(), then event_set(), then event_add() again.
That's necessary for correctness with Libevent 1.x and 2.x as well.

My apologies if I haven't understood the situation, though; if you
could post a tiny code sample demonstrating the behavior you're
talking about, that would probably help track down the issue.

best wishes,
-- 
Nick
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