Re: [boost] asio networking proposal

From: Christopher Kohlhoff (chris_at_[hidden])
Date: 2005-09-02 07:28:31

Hi Rob,

--- Rob Stewart <stewart_at_[hidden]> wrote:
> Was that 100 bytes per async call or per type of call?

Per type of call/callback handler combination.

> As I understand it, you have a class template derived from
> win_iocp_operation.

Several class templates, yes.

> Is it 100 bytes for each class created by
> specializing that template?

Yes, for each class that instantiates the template.

> Is there a reasonable upper bound on
> the number of such types in a given application?

No, I don't think so. An app can make as many asynchronous calls as it
wants using any combination of types for a callback handler. This even
includes things like call demuxer.post(...) to cause a deferred
invocation of a function object.

One of the strengths of an async I/O approach is that it makes it
relatively easy to compose new asynchronous operations from others. For
example, you might define a function:

  template <typename Stream, typename Handler>
  void async_read_mymsg(Stream& s, mymsg& m, Handler h);

which is is implemented internally using a chain of calls to async_read
or async_read_n. Each one of these internal async calls would require
its own win_iocp_operation-derived template instantiation, and each one
of those types would also be dependent on the Handler type. So in that
case the number of win_iocp_operation-derived template instantiations
would be the number of internal handlers x the number of different
handlers used with async_read_mymsg. And there could be further layers
of composition... you get the idea.

Cheers,
Chris