[Libevent-users] deferred callbacks and evbuffer cleanup_cb

[Jan Heylen <heyleke@xxxxxxxxx>]

Hi,

I'm trying to use evbuffers, cleanup_cb, and the deferred callbacks.

some background:
* using (tcp) sockets
* sending data over the socket: in first place try to write
(evbuffer_write), if you get 'wouldblock' postpone the write by using
bufferevent_write_buffer. Main reason is we don't need to keep the
user's data in most cases and the dat is send immediatly.
* after sending data, a 'send cb' should be called to the user who
wanted to send something.

Now, when looking at the best way to get the cleanup happening (and a
mechanism to let the user know his data is send), I was looking at
both evbuffer callbacks and the evbuffer cleanup_cb.
I'm thinking on using the cleanup_cb, as it is only called when the
chain, the actual data, gets freed, so I can be sure the data is out.
With evbuffer callbacks, the original evbuffer gets drained upon call
to bufferevent_write_buffer already, and not when the data itself is
really 'out', so that means, I have to make a distinction.

However, If I look at the code, these cleanup_cbs are not and cannot
be 'deferred'. So in the first place, when using evbuffer_write, the
cleanup_cb will happen on the stack, and so also my 'data is send'
callback, would happen on stack (and so cb will happen before the
sending data function returns).

Questions:
* thinking about the 2 different paths on getting data out,
(evbuffer_write and postponed via bufferevent_write_buffer), what
would be the best mechanism to get the 'all data is out' cb mechanism
working for them both?
* Is it a design choice to not defer the cleanup_cb, or would it make
sense to add it?

kind regards,

Jan Heylen
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