Hi Philip,
Here is a simple example of how I create events that I want to fire
explicitly (ie: user triggered). I just happen to be working on this code
right now. I do this sort of thing all over the place. Especially useful to
wakeup a base on a different thread (assuming you are set up for thread
safe operation).
// this is the callback that does the work
void udp_check_txq(int fd, short event, void *arg)
{
UdpChan_t *udp = (UdpChan_t *)arg;
process_tx_queues(udp); // my function not shown here
}
// arm the "user event" to be executed 'now'
void udp_arm_check_txq(UdpChan_t *udp)
{
// add the event with a 0 timeval
// it will be called on next event loop
struct timeval tv={0,0};
evtimer_add(udp->check_txq_ev, &tv);
}
// Create the event in some init code
if ( !(udp->check_txq_ev = event_new(base, -1, 0, udp_check_txq, udp)) )
{
break;
}
// Call udp_arm_check_txq() when you want to make the event immediately
ready
// It will called on the very next event loop
udp_arm_check_txq(udp);
-Bill
On Sun, Sep 11, 2016 at 1:31 PM, Philip Prindeville <
[email protected]> wrote:
> Figured I'd copy the list on an email I sent Nick about user-triggered
> events in case anyone else wanted to chime in (or contribute a patch!).
>
> -Philip
>
> To: Nick Mathewson <[email protected]>
>> From: Philp Prindeville <[email protected]>
>> Subject: Question about libevent documentation
>> Message-ID: <[email protected]>
>> Date: Sun, 11 Sep 2016 11:18:40 -0600
>>
>> Hi.
>>
>> Thanks for providing this document. It's been really helpful. However,
>> I'm looking at:
>>
>> http://www.wangafu.net/~nickm/libevent-book/Ref4_event.html
>>
>> where it says:
>>
>>
>> Working with events
>>
>> Libevent's basic unit of operation is the event. Every event
>> represents a set of conditions, including:
>>
>> * A file descriptor being ready to read from or write to.
>>
>> * A file descriptor becoming ready to read from or write to
>> (Edge-triggered IO only).
>>
>> * A timeout expiring.
>>
>> * A signal occurring.
>>
>> * A user-triggered event.
>>
>> but there's no description of user-triggered events. I'm working with
>> some overly complicated legacy pthreaded code (which uses DBus) and I'm
>> trying to convert it piecemeal (since my boss doesn't want to allocate
>> the time to a big-bang re-write) to be event-driven.
>>
>> Problem is that there are certain events which I need to be able to
>> model (like queues becoming empty/non-empty/full) and these will need to
>> be "user-triggered" events, but I can't see from the documentation how
>> to do this that fits well with our requirements:
>>
>> I looked for some documentation elsewhere how to do this and saw your
>> stackoverflow posting:
>>
>> http://stackoverflow.com/questions/7645217/user-triggered-
>> event-in-libevent
>>
>> but nothing that's "clean" comes up (either using an unneeded timer
>> interval, or else using undocumented functions which might change/go
>> away in the future).
>>
>> Any chance of adding a couple of paragraphs on the best way to do this?
>>
>> And it would be nice if the event could be added to the loop via
>> event_add(), and that the handler for that event was subject to the same
>> constraints (like priorities, max-dispatch interval, debugging with
>> event_base_dump_events(), etc). Also, if you're doing profiling, then
>> you don't want the event that's setting the user-trigger to be "charged"
>> the time it takes the user-triggered event to run in addition to its own
>> time... it's misleading.
>>
>> Lastly, you might have several high-priority events that run quickly and
>> want to "fire" the user-triggered event, but not actually have it run
>> until low-priority events can be dispatched... and then only once (i.e.
>> once per event-base loop dispatching iteration).
>>
>> What do you think?
>>
>> Thanks,
>>
>> -Philip
>>
>> P.S. I might be sending you a patch to bind a source address to a
>> bufferevent socket...
>>
>
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