Re: [pclasses-devel] plugin registry thoughts

[Christian P. <cp...@se...>]

Am Donnerstag 20 Januar 2005 18:45 schrieb stephan beal:
> A potential solution came to mind today:
>
> When Factory::create(classname) is called, we count how many times any
> given classname is passed. In a garbage collector thread we iterate the
> factory maps every now and then and remove any factories which have 0
> hits.

For this to work we have to add reference-counting to the Factories, which 
implies that we also need to track object destruction, and this is where it 
gets tricky.

> The implementation for the actual tracking would be fairly trivial: one
> more map added to Factory, which gets modified during create(), plus a
> cleanup function:

as i said, it's not that trivial.
We could add a wrapper template which does the reference counting for 
class-types created by the factories.

> The GC thread would then call
> Factory<T>::instance().cleanUnusedFactories() every X seconds (5+
> minutes is probably reasonable, or after every X factory registrations
> we check for unused facs). i propose to make hitsMap() internal so that
> we can achieve safe locking more easily. If hitsMap() is public we
> don't need cleanXXX(), as any 3rd-party code could directly manipulate
> the factory map. While this isn't a problem in and of itself, it might
> become problematic in a multi-threaded environment. Thus the cleanXXX()
> member, to simplify any potential locking.

I don't like the idea of having an implicit GC thread.

> More complex variants might track how long ago a given factory was used,
> or how often, or use a LRU algo with some built-in limit of factories
> to hold on to.

But wee also need some "plugin filesystem registry" which tells the P plugin 
loader which shared objects must be loaded for a particular class type that 
should be constructed.

We actually have two different problems:
1. Plugin registry (only load plugin-lib's that are really needed)
2. Factory reference counting (cleanup of unused factories)



Greetings,
Christian