Excerpts from Tomas Carnecky's message of Mon Apr 12 06:25:23 -0600 2010:
> I have a patch which adds support for hooks which are run when tags are 
> added, removed or new messages added to notmuch. But perhaps the 
> fork/exec overhead of running the hooks would slow the processing down 
> too much.

Rather than a fork/exec for every message, why not have a persistent
subprocess that receives message IDs (+ filenames?) and can then do
arbitrary work and return back the proper tags?