Re: [Libevent-users] Wait until the loop thread processes all the data?

[Azat Khuzhin <a3at.mail@xxxxxxxxx>]

On Tue, Feb 20, 2018 at 02:03:41PM +0300, Egor Tensin wrote:
> Hello,
> 
> Hopefully you can help me with a libevent issue that I'm stuck on. I
> have two threads, one of which produces data, and the other runs
> event_base_dispatch (receiving the data from the first thread,
> processing it and sending it somewhere else). They communicate using a
> pair of bufferevents (over a local socket pair). The issue is, the
> first thread might be done with producing the data, program
> termination being the next logical step. But I want to wait for the
> second thread to 1) receive _all_ the data the first thread sent, 2)
> process it and 3) send it to the final destination. I can't figure out
> how to accomplish that, because if I call event_base_loopexit after
> the first thread stops, it looks like the second thread exits right
> after executing the current round of callbacks, discarding the latest
> data that might have been sent by the first thread. Can somebody
> please explain to me how to fix this? I can set a random timeout for
> event_base_loopexit, but this is unreliable, isn't it?

Can you share an example?

Do you have two event_base, i.e. one loop per thread?

In this case if you stops the producer's loop you have to do this only
once it send all data, and if you use event_base_loopexit() (and not
event_base_loopbreak()) then it is likely that all data will be sent,
since the loopexit handle all queued events before exit.

And so after, you should event_base_loopexit() of the consumer's thread,
once it receives all data (I don't know), and basically most of the time
it will be enough to just call event_base_loopexit() again. But not
always, since there can be some data pending, so maybe you want to
implement some logical exit, i.e. once you receive *complete message*.

And like Aaron suggests it can be enough to call loop with EVLOOP_ONCE,
but sometimes it will hang the program (in case you don't have data to
process, i.e. very fast exit)

Regards,
Azat.
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