Re: [Libevent-users] event_base_loop: wait for events to be added by other threads?

[Evan Jones <evanj@xxxxxxx>]

On Dec 3, 2010, at 15:47 , Nick Mathewson wrote:
> A quick heads-up here that you'll want to know: there's a bug in
> 2.0.9-rc and earlier where activating an event from another thread
> doesn't wake up the loop immediately.  It should be fixed in 2.0.10;
> see commit 5beeec9d43cb.

Yeah, I saw that one already thankfully.

> Wow, good timing.  I actually coded up an example patch to try to do
> this earlier this week; have a look at branch "21_evloop_emptyok" in
> my github repository [git://github.com/nmathewson/Libevent.git] and
> see if it looks okay to you.  I don't like the EMPTYOK name, but the
> rest of it seemed ok.

Oops! There goes an hour or two of my life. Your patch is basically  
equivalent to mine, except that I verify that the event_base has locks  
enabled, since otherwise the EMPTYOK option doesn't make sense. If  
EMPTYOK is passed without locks, I call event_err().


> ONCE means wait till at least one non-internal callback is activated,
> then to run until there are no active callbacks.
> EMPTYOK|ONCE means wait till at least one non-internal callback is
> activated, then to run until there are no active callbacks, EVEN IF we
> didn't start with any pending events.
> NONBLOCK means to check events and run user callbacks until no more
> pending events want to be activated.
> EMPTYOK|NONBLOCK means to check events and run user callbacks until no
> more pending events want to be activated, EVEN IF we didn't start with
> any pending events.


This seems like a good interpretation, and makes sense now that I  
think about it.

> ONCE|NONBLOCK doesn't seem reasonable to me atm.

Adding an event_err() for that combination might make sense then?

Evan

--
Evan Jones
http://evanjones.ca/

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