Re: [Boost-users] [Boost.ASIO] and registering callbacks?

From: Tim St. Clair (timothysc_at_[hidden])
Date: 2008-07-02 09:13:07

James -

    I'm sure others can better explain the internal reasons "why"- (I
believe you are enqueing work to the proactor).

http://www.boost.org/doc/libs/1_35_0/doc/html/boost_asio/design/async.html

    On the "how", you are correct.  If you look at the examples, you have to
enque operations in your async (read_callback).

http://www.boost.org/doc/libs/1_35_0/doc/html/boost_asio/examples.html

http://www.boost.org/doc/libs/1_35_0/doc/html/boost_asio/example/http/client/async_client.cpp<-
as well as the other async examples

   Typically I do the following, which I gleened from the examples:
       async_read_some ()
       check if message is complete
       if so notify() listener(s)
       async_read_some()

Cheers,
Tim

On Wed, Jul 2, 2008 at 7:11 AM, James Vanns <james.vanns_at_[hidden]>
wrote:

> Hi, I don't quite understand how to register an async call back once with
> an IO service? Consider this model:
>
> * Server accepts connection
> * connection object *registers* it's read callback (to be executed whenever
> there is a
>  read available from the underlying epoll)
> * connection object is doing some processing or conversing with the main
> server etc.
> * epoll (or IO service) says there is data to be read
> * call back gets executed
> * the processing resumes (based on the newly received data)
>
> I'm prettu sure that is normal. But how do I actually achieve this with
> ASIO? I mean, I have the main server that runs io_service::run() so it knows
> when there is data to be read on a socket - that socket is of course
> associated with this client connection object and it is this object that
> acts on the data (and may also send of course). However, using the
> async_read methods I appear to have to keep re-registering the callback in
> the actual callback:
>
> client::register_read_callback()
> {
>    m_socket.async_read_some(buffer(m_inbound, p_max),
>                             boost::bind(&base_io::read_callback,
>                                         shared_from_this(),
>                                         placeholders::error,
>                                         placeholders::bytes_transferred));
>
> }
>
> client::read_callback(error_code &ec, size_t bytes)
> {
>   // I have to call register_read_callback() again here!
> }
>
> client::start() // I get called when I am established between two endpoints
> {
>   register_read_callback();
>   do_some_processing();
> }
>
> client::do_some_processing()
> {
> }
>
> I'm trying to build a library that transparently buffers messages received
> from an endpoint. THe library silently receives the data (through the epoll
> based io service and the asio tcp sockets), builds the messages from the
> received data and puts them in a stack ready to be poppped off by an
> application calling pop_msg().
>
> I'm having difficulty in separating these two operations.
>
> Regards,
>
> Jim Vanns
>
> --
> James Vanns
> Systems Programmer
> Framestore CFC Ltd.
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users
>

-- 
Regards,
Timothy St. Clair
[timothysc_at_[hidden]]