On Mon, Sep 3, 2012 at 1:05 PM, Parvez Shaikh <pshaikh.wo...@gmail.com>wrote:
> 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.
>
If you must create your messages in another thread (maybe it is cpu bound,
or you must use blocking operations), this should work. But if you don't
have too, I would not use threads since I don't like deadlocks :-)
Anyway, when the send fails with EAGAIN, you want to enable EV_WRITE, so
you can continue to drain your messages queue when socket is ready. The way
you work with EV_WRITE is not related to working with threads.
> 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
>>>>
>>>> ***********************************************************************
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>>>>
>>>
>>>
>>
>
