Re: [boost] [Fibers] Performance

Subject: Re: [boost] [Fibers] Performance
From: Gavin Lambert (gavinl_at_[hidden])
Date: 2014-02-02 17:05:30

On 31/01/2014 22:28, Quoth Bjorn Reese:
> Consider a secure RPC server, whose full API only can be used if the
> client has the correct privileges. For simplicity, let us assume that
> this is a single-client server. There are two modes: unauthenticated
> and authenticated. In unauthenticated mode, the server should reject all
> but the authentication requests. The way you typically would do this is
> to have separate implementations of the API for each mode, and when the
> client has been authenticated, the server will switch from the
> unauthenticated to the authenticated implementation. This wholesale
> replacement of the underlying implementation is much more difficult
> to do with the parallel initiator-callback style. We could solve the
> problem with another level of indirection, but that would effectively
> re-introduce the event listener.

The way to handle that, I would think, would be to have the "public" API 
be more limited in scope (not an identical copy that mostly returns 
not-authenticated errors), and to provide an "async_authenticate" 
request that calls back (single-shot) with an interface that provides 
the complete API.

Async requests wouldn't carry over between the authenticated and 
unauthenticated API, but you wouldn't want that anyway -- most clients 
would authenticate first before making any other requests anyway, and 
one of the clients might be a "broker" that wants to maintain multiple 
independently authenticated connections with different credentials.

Granted that's outside the scope of a single-client server, but the 
design would be easier to scale if it turns out that single-client isn't 
sufficient.

Again, I'm not saying that Asio-style callbacks are the "best" way of 
implementing RPC or UI models.  Just that it's not impossible to do so. 
  (But at some level, you need a serialisation+networking layer to 
actually transfer requests between processes or machines.  This can be 
made completely transparent to both server and client, but something has 
to be able to translate all the possible types of request.)