Forum OpenACS Development: Re: Usage of XoTCL objects vs. database queries

Posted by Stefan Sobernig on

Would ttrace help here ( ? Probably not, because it still requires me to make the object known to the thread and creating a resource copy in that thread.

You already hinted it, ttrace addresses a different issue. ttrace does not realise sharing of commands, procs (and objects), it solves the problem of the eager initialisation of interpreters. Based on Tcl's unknown mechanism, it sources procs on demand. This helps to address the issue of AOLServer/ Naviservers extensive blueprinting need ... unfortunately, it provides challenges to tcl's (and xotcl's) introspection mechanism which assume an entirely initialised surrounding ...

But it's not the same as using the same object copy in memory, as each thread has it's own copy of the ns_cache object and I can manipulate each of them independently.

Indeed, you don't have a shared state, compartimentalised into objects, available. If you try to achieve that, you may choose a different strategy: Realise object representations by ns_set et al. ... XOTcl slots provide an elegant way of introducing such an representation strategy, instead of accessing per-object state (in the strict sense), the slot-provided accessor/mutator methods write to and read from ns_sets ... Well, this implies other remedies and might not be scalabale open-end, but may be a valid optimisation strategy ... Objects residing in each thread are then mere PROXIES to a single shared state, under a single, db-provided identity.

Posted by Andrew Piskorski on
Stefan, that's very interesting... So rather than using ns_set, can XOTcl transparently layer its objects on top of nsv/tsv?

tsv::lock makes it easy to atomically perform multiple tsv commands, which might be ideal for implementing that sort of safe transparent multi-threaded object access in XOTcl.

However, I don't see any direct mention of this sort of stuff in the XOTcl docs nor its slots tutorial. Is there better info or examples somewhere on using XOTcl slots in this way?