Re: [boost] asio formal review - demuxer

From: Andrew Schweitzer (a.schweitzer.grps_at_[hidden])
Date: 2005-12-27 16:56:43

Rene Rivera wrote:
[snip]
> Andrew Schweitzer wrote:
>>I think the library design or naming might be a bit confused on this 
>>point (or quite possibly it's me).
> 
> 
> The fact that it's confusing, even when looking at the code, is a point 
> against the design ;-) OK, I'm rereading the code, instead of relying on 
> memory...

Yes, although I think I'd say maybe it's not a design issue but just 
that the documentation isn't as complete as the code.

> 
>>As far as I can tell two things are true:
>>   1) the demuxer ends up with two actual services in its list after it
>>      is constructed:
>>       a) demuxer_service
>>       b) win_iocp_demuxer_service (or the selected
>>          platform-implemenation of demuxer_service)
> 
>
> OK, AFAICT it only ends up with (b) in the service_registry.

Ok, time for debugger.

[runs debugger]

I think it's a and b. VC7.1 debugger appears to show that 
service_registry_.first_service_ points at a demuxer_service, and the 
demuxer_service's node's next_ member points at win_iocp_demuxer_service.

I think here's how the code works:
1) demuxer::demuxer calls get_service<demuxer_service>
2) get_service finds nothing in the service_registry_, so it creates a 
new demuxer_service.
3) demuxer_service::demuxer_service calls 
get_service<win_iocp_demuxer_service>
4) get_service doesn't find a win_iocp_demuxer_service in 
service_registry_, so it creates a new one, and adds it. It returns.
5) demuxer_service::demuxer_service returns
6) the first call to get_service now adds the new demuxer_service to the 
list.

> 
> 
>>   2) the demuxer also has a PIMPL relation with demuxer_service,
>>      and demuxer_service has a PIMPL relation with
>>      win_iocp_demuxer_service
> 
> 
> Yes. I guess the key point here is that there's only 1 (singleton) of 
> win_iocp_demuxer_service for all demuxer_service instances in the same 
> basic_demuxer instance? (again AFAICT)
> 

Yes I think there's only one win_iocp_demuxer_service, within that 
particular instance of the demuxer. I think get_servive<ServiceType> 
guarantees there's only one list member of a given ServiceType, by using 
  the language's typeid operator.