Re: [Libevent-users] On which thread does bufferevent filter run, and when?

[Nick Mathewson <nickm@xxxxxxxxxxxxx>]

On Wed, Jan 29, 2014 at 4:52 PM, Yucong Sun <sunyucong@xxxxxxxxx> wrote:
> On Wed, Jan 29, 2014 at 12:42 PM, Nick Mathewson <nickm@xxxxxxxxxxxxx> wrote:
>> On Sun, Jan 26, 2014 at 2:58 AM, Yucong Sun <sunyucong@xxxxxxxxx> wrote:
>>> Hi there,
>>>
>>> So I need to implement a zlib bufferevent filter to transparent
>>> compress the data passing through a bufferevent. and but I want the
>>> zlib work to be done in a separate thread to offload main loop.
>>>
>>> I currently call bufferevent_write() on main thread, would the filter
>>> code executed immediately?  if I call  bufferevent_write() from
>>> another thread, would the code be executed over that thread instead?
>>> (locking is all properly setuped).
>>
>> The thread in which callbacks happen isn't currently specified by the
>> documentation.  So it is allowed to change in future versions.
>>
>> In practice right now, I believe that filters are greedy: they consume
>> all input as soon as you give it to them, and they process data from
>> the underlying bufferevent as soon as it's read.  They do this in the
>> same thread where the they receive the data.  (This is affected by
>> watermarks on the underlying bufferevent.)
>
> I don't quite understand this, what "callback" were you referring to?
> When I call bufferevent_write() on a filtered socket based
> bufferevent,   would the filters  A) get executed recurisvely on the
> current thread/stack ? Or would B) it internally add some more events
> to the loop and executes the filter code on next callback?

I believe that, in the current code, the filter callbacks (that is,
the functions that you provided to implement the filter) get called on
the stack.

-- 
Nick
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