[PATCH 0 of 3 V2] move cache files to a collected cache folder .hg/caches/

[Adrian Buehlmann]

On 2011-01-02 06:03, Jason Harris wrote:

Ok. I just skimmed through this part of your texts again. See my
comments below.

> One problem with adding a copener instead of just changing the paths "in situ",
> is that if after setting up copener, changes are later made to the repo's opener
> than the copener doesn't get these changes. Ie the copener later has to be
> synchronized with the opener anytime the opener changes. Such synchronization
> things *alway* break be it sooner or later. In fact the test suite caught one
> such change in localrepo.py where in a place deep in the code
> self.opener.createmode was changed, and one of the tests then failed with the
> cache directories being created in the wrong mode. The fix was of course to make
> the same change to self.copener.createmode. In any case we have taken something
> very simple and abstracted it a bit into something that to me is not quite as
> clear.

Not sure what changes your are referring to in there, but this is a
non-issue and pretty much a red herring.

All that's needed for setting up copener is (as you demonstrated
yourself in your patch 3):

diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -33,6 +33,7 @@
         self.auditor = util.path_auditor(self.root, self._checknested)
         self.opener = util.opener(self.path)
         self.wopener = util.opener(self.root)
+        self.copener = util.opener(os.path.join(self.path, "caches"))
         self.baseui = baseui
         self.ui = baseui.copy()

@@ -93,6 +94,7 @@
         self.sopener = self.store.opener
         self.sjoin = self.store.join
         self.opener.createmode = self.store.createmode
+        self.copener.createmode = self.store.createmode
         self._applyrequirements(requirements)
         if create:
             self._writerequirements()

This is a whole lot less fragile than repeatedly inserting

   os.path.join("caches", ...)

wherever a cache file needs to be accessed.

The copener approach has the benefit that the directory name of the
cache directory is defined in *one place* -- something which is pretty
much standard in programming.

Also the "knowledge" that the string "caches" must be path-joined to
access "The Mercurial cache" is encapsulated in copener.

The opener approach taken by Mercurial is a bit unusual, but as soon as
you have understood how it works, it is pretty simple. You can just call
the opener like any function object and it will open the file in the
right place for you, doing whatever is needed to open that file in that
location. And it encapsulates the policy that needs to be followed to
access files in that place.

You might even be able to have a special cache opener behavior in the
future, possibly side-stepping things like the hardlink dance that is
done in class util.opener. It might also be possible to speed up things
further by side-stepping util.opener's makedirs dance: all files are in
the caches directory itself, there are no subdirs anyway that would need
to be created. All that needs to be created is the "caches" (or "cache"
dir -- as I have proposed). These improvements would all be possible if
you used a separate cache opener.

But as I said, you are free to wait for Matt or a crew member (or
whoever would like to :) to chime in.