[Gnump3d-devel] Idea for realtime tagcache updating

[Stuffed Crust]

On Sat, Feb 19, 2005 at 09:30:29PM +0000, Steve Kemp wrote:
> > I'm also working on a method to update the stored tag cache on the fly, 
> > so we don't need to manually re-run gnump3d-index to pick up those extra 
> > files.  
> 
>   I think I said in a previous reply this seems like a good plan.

I've been thining about this a bit, and I'd like to float this past you 
to see if there are any gotchas that I may have missed:

Child discovers file is not in cache.  Parses out tags, appends them to 
CACHEFILE_NEW.  (using O_EXCL access to prevent other children from 
hitting the file and screwing us up concurrently).

Parent, on the next loop cycle, notices the presence/update of
CACHEFILE_NEW, and loads it into the cache for subsequent children to
benefit from.  (we update the master cache file in a similar manner).

The next time gnump3d-index is run, it loads up both CACHEFILE and 
CACHEFILE_NEW before donig its traversal, writes everything out into 
CACHEFILE then erases CACHEFILE_NEW, finally HUPping the server so that 
it loads up the new cache file.
 
 . . .

So far, there's only one problem I see -- There could be a race between
two children trying to read the same directory, both deciding to parse
tags/update the cache.  We could then end up with duplicate entries in 
CACHEFILE_NEW, which isn't all that terrible.  I don't see any way 
around this concurrency problem though, at least not without going to 
threads (and that'll introduce its own mess that IMO is really not worth 
the hassle)

 - Solomon
-- 
Solomon Peachy                                   ICQ: 1318344
Melbourne, FL                                    JID: address@hidden
Quidquid latine dictum sit, altum viditur

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