Re: [Libevent-users] How to activate read callback when not all data was read

[Sanjiv <sanjiv.raj@xxxxxxxxx>]

Hi Nils,

I have a similar use case and I am following the approach described below.

1. Determine an ideal low watermark for the read callback.

2. I'm not sure if there are any disadvantages to this approach, but you could try to read within a loop inside the read callback till there is no further data to be drained. i.e on each read callback read as much data as possible.

Hope this works.

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Thanks

Sanjiv

On Tue, Apr 10, 2012 at 2:40 PM, Nils Rennebarth <nils.rennebarth@xxxxxxxxx> wrote:

Hi,

In my daemon which uses libevent, i use bufferevent to read client commands
from a socket, set everything up to eventually generate the reply, and return to
the event loop.

Now a client may send several commands in one go. If I only read the first
command and drain the corresponding bytes from the bufferevent's input
buffer, the read callback will not be called until *more* data arrives,
so if a client sends two commands in one go, I need to somehow queue
the second (and further) commands before returning to the main loop,
otherwise the commands never gets processed.

Is there some other way, to get the second command processed,
something like "return to the main loop, but mark this callback as
still pending, and call it again"

In other words, bufferevent forces me to do edge-triggered event
handling. Is there a way to let me do level-triggered event handling
instead.

Or is there something like a idle task, that get called when there is
nothing else to do? Working with timeouts would introduce arbitrary gaps
in command handling, event if there are no other clients that want
work, so I won't go that route. Or does setting a timeout of { 0, 0 }
work?

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Mit freundlichen Grüßen / with kind regards

Nils Rennebarth, Software Developer

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Sanjiv Raj


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