Thanks Oleg and Nir.
I am also pursuing another approach. Here I have defined a custom event
(associated with FD but not having either EV_READ or EV_WRITE) and there is
no time out either.
A thread queues data to "outgoing message list" and activates an event. In
response to this, event reactor thread (one with dispatch) calls a function
that sends message from this list one by one until "send" encounters EAGAIN.
Requesting your feedback on this approach.
Thanks
On Sun, Sep 2, 2012 at 3:45 PM, Nir Soffer <nir...@gmail.com> wrote:
>
>
> On Sun, Sep 2, 2012 at 6:54 AM, Parvez Shaikh <pshaikh.wo...@gmail.com>wrote:
>
>> Thanks Oleg,
>>
>> Second approach is what I am doing.
>>
>> Why disabled EV_WRITE in write callback?
>>
>> I'd wish to have this callback called again whenever send buffer has
>> space, so disabling EV_WRITE will prevent this.
>
>
> You want to enable EV_WRITE only when you have something to write.
>
> When you enable EV_WRITE, libevent will add the descriptor to the the
> event backend (e.g select). When the descriptor is ready for writing, the
> write callback will be called. If you always enable EV_WRITE, the callback
> will be called on every loop iteration, and the event loop will never wait
> for events, since the descriptor is almost always ready for writing.
>
>
>>
>>
>> On Fri, Aug 31, 2012 at 3:54 PM, Oleg <mybrokenb...@gmail.com> wrote:
>>
>>> EV_WRITE calls whenever you can write to send buffer until it's not full.
>>> So if you have never called send(), but EV_WRITE is enabled you will
>>> receive this event each new loop (your CPU will be ~100% used).
>>> If you have called send() and it didn't return EAGAIN you will also
>>> receive this event next loop.
>>> If you have called send() and it returned EAGAIN you will receive this
>>> event when your send buffer will have some free space.
>>>
>>>
>>> So for your sending queue it should look like this in pseudo code:
>>>
>>> 1) Application->Send(data)
>>> {
>>> if (send() != EAGAIN )
>>> return;
>>> else
>>> {
>>> queue.push(data);
>>> enable(EV_WRITE,onWriteCallback);
>>> }
>>> }
>>>
>>> 2) onWriteCallback()
>>> {
>>> while(!queue.empty)
>>> {
>>> if (send(queue.front())== EAGAIN);
>>> return;
>>> queue.pop();
>>> }
>>> disable(EV_WRITE);
>>> }
>>>
>>> 31.08.2012, в 8:50, Parvez Shaikh написал(а):
>>>
>>> > Hi all,
>>> >
>>> > I have a question about EV_WRITE event as to when does it's callback
>>> function invoked?
>>> >
>>> > Is it that when someone first executes write on an fd associated with
>>> EV_WRITE event?
>>> >
>>> > Or when libevent detects that application can now write to fd without
>>> getting errors?
>>> >
>>> > For EV_READ it is easy to understand that it's callback is invoked
>>> when data is available for read on fd but not clear about EV_WRITE.
>>> >
>>> > Here is what I am trying to do -
>>> >
>>> > I am trying to write asynchronous send/recv application; in which I
>>> will read data on connected sockets asynchronously using "EV_READ's
>>> callback.
>>> >
>>> > For send however, I will enqueue the data to be sent in my own
>>> queue(application will write data to this buffer) and I will flush the
>>> buffer in EV_WRITE callback.
>>> >
>>> > Now if I get the error EAGAIN in send operation in callback of
>>> EV_WRITE, I will simply return and on next invocation of EV_WRITE's
>>> callback I will start flushing my buffer again.
>>> >
>>> > Thanks,
>>> > Parvez
>>>
>>> ***********************************************************************
>>> To unsubscribe, send an e-mail to majord...@freehaven.net with
>>> unsubscribe libevent-users in the body.
>>>
>>
>>
>
