When to use invalidate()

[Steve Borho]

On Mon, Feb 1, 2010 at 6:34 PM, Greg Ward <greg at gerg.ca> wrote:
> Hi all --
>
> I have an extension that keeps too much data in memory.  (It's my
> "bugmap" extension that associates changesets and bug IDs.  Uses a
> local flat file for short-term storage and a remote MySQL database for
> long-term.  It keeps a copy of the local file, a MySQL connection, and
> a cache of info queried from MySQL in memory.  It uses that info to
> doctor the value returned by changectx.description() so that mutable
> bug IDs appear in any log output.)
>
> This is no big deal at the command line, but I have several related
> bugs that appear in long-running processes like TortoiseHg and hgweb
> (I'm using mod_wsgi):
>
>  * MySQL errors because the database connection used by the extension
> stays open and the server got restarted
>  * out-of-date information: someone pushes new changesets to the
> repo, and hgweb correctly shows them, but bugmap fails to augment the
> display with bug info (which it correctly does for changesets that
> existed initially)
>
> In all cases, the workaround is to restart the long-running process.  Lame.
>
> I *thought* the right fix was to wrap localrepository.invalidate() and
> use that to discard my extension's state.  Then on the next request,
> it would re-read the local bugmap file, reopen the database
> connection, etc.  But that doesn't work: hgweb doesn't even call
> invalidate()!  TortoiseHg seems to call it a lot, but I have not read
> the code to see when or why.
>
> So, two questions:
>
> 1) what is the right way for an extension to discard unwanted state at
> the end of a request (or similar processing phase, e.g. GUI refresh)?
> 2) what is the purpose of localrepository.invalidate() and when is it
> normally called?

FWIW: THG calls repo.invalidate() at every refresh event.  Perhaps
overkill, but we get bitten a lot by state mismatches from people
using the CLI while keeping our tools open for a long time.  See
invalidaterepo() in tortoisehg/util/hglib.py

--
Steve Borho