[spambayes-dev] Feedback requested on an external lockfile module...

[skip at pobox.com]

All this business about safely writing pickles got me to wondering about
locking files.  Rather than implement something which was
SpamBayes-specific, I scouted around a little bit then implemented something
which hopefully

  * has a reasonable API (I think)
  * is cross-platform
  * allows multiple different implementations (currently one each based on
    os.link and os.mkdir and one which uses a SQLite database to maintain
    lock info)
  * might someday be good enough for inclusion in Python proper as the One
    True Way to do advisory file locking.

The result is the lockfile module, which you can find at your local
neighborhood (virtual) cheese shop:

    http://pypi.python.org/pypi/lockfile/

I've done a fair amount of testing on my Mac.  (It has a fair number of
doctests.  Thank you again Uncle Timmy.)  Scott Dial (from the python-dev
mailing list) ran it through its paces on Windows a bit and sent me some
revisions.  Other than Scott's inputs I've received no direct feedback on
the module, though when I first raised the idea of one-lock-mechanism-to-
rule-them-all it generated a few comments.  I suspect Py3k and an impending
2.5.2 release are probably sucking up all available Python developer round
tuits.

Today I added lockfile usage into Dave Abrahams' safe_pickle function, in
the process renaming it to safe_pickle_write and adding a corresponding
safe_pickle_read.  I then replaced all pickle.{dump,load} calls with the
relevant safe_pickle_{write,read} functions.

This code has not been checked in yet.  I've attached a diff against the
current rev 3168.  I'm interested in how people think I should proceed.
Some possibilities:

    * throw it out - we don't need dependencies on external crap
    * keep it but pull lockfile into the spambayes package for ease of
      distribution
    * check the changes in on head
    * create a branch and check the changes in there
    * get 1.1 out the door, damn it!  leave this for 1.2 (around 2011)
    * keep the safe_pickle_{read,write} functions but take out the lockfile
      stuff.

Feedback please.

Thx,

Skip

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