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