Fix config.parse_if_needed cache invalidation

[Peter Suter]

42:ticket:5525 noted:

It appears there is an unused protected attribute _cache in [9037#file11]: tags/trac-1.0.2/trac/config.py@:293-294#L264​. Could that be removed?

But perhaps some other variable was meant to be cleared, e.g. self._sections = {} or for k in self._sections: self._sections[k]._cache = {}.

It looks like this scenario would currently fail and be fixed by that cache invalidation:

# config inherits parent.ini containing [a] b=x
config.get('a', 'b') # caches 'x' in config._sections['a']._cache['b']
# change parent.ini to [a] b=y
config.parse_if_needed() # does not invalidate that cache
config.get('a', 'b') # should return 'y' but returns cached 'x'

We should add a testcase and fix the code.

[Ryan J Ollos]

The patch looks correct, but I was having some trouble reproducing any issues in a Trac instance. It looks like this is due to the Environment object being destroyed​ when a configuration change is detected. Regardless, I think we should fix the issue. I have a minor refinement that I'll post shortly.

[Peter Suter]

Replying to rjollos:

I was having some trouble reproducing any issues in a Trac instance. It looks like this is due to the Environment object being destroyed​ when a configuration change is detected.

Yes, sorry I forgot to mention that. With Trac alone as a blackbox the issue does not seem to be externally observable. The calls to parse_if_needed in Trac seem to be uncritical due to circumstances as pointed out.

I did not thoroughly check plugins, but it looks like ​th:AccountManagerPlugin may be affected.

[Ryan J Ollos]

• It looks like an instance of self._sections = {} can be removed: tags/trac-1.0.2/trac/config.py@:271#L264​. The main Configuration object and every parent will set changed = True, which will clear _sections before the recursively-called function exits.
• Maybe we could use wait_for_file_mtime_change​ to avoid the time.sleep(2)?

I added those changes to rjollos.git:t11902-parent-invalidates-config-cache.

[Jun Omae]

…

I added those changes to rjollos.git:t11902-parent-invalidates-config-cache.

Looks good to me.

[Ryan J Ollos]

Committed to 1.0-stable in [13628], merged to trunk in [13629].