[GSoC14][RFC] Proposal Draft: Refactor tempfile handling

[Brian Gesiak <modocache@gmail.com>]

Hello all,

My name is Brian Gesiak. I'm a research student at the University of
Tokyo, and I'm hoping to participate in this year's Google Summer of
Code by contributing to Git. I'm a longtime user, first-time
contributor--some of you may have noticed my "microproject"
patches.[1][2]

I'd like to gather some information on one of the GSoC ideas posted on
the ideas page. Namely, I'm interested in refactoring the way
tempfiles are cleaned up.

The ideas page points out that while lock files are closed and
unlinked[3] when the program exits[4], object pack files implement
their own brand of temp file creation and deletion. This
implementation doesn't share the same guarantees as lock files--it is
possible that the program terminates before the temp file is
unlinked.[5]

Lock file references are stored in a linked list. When the program
exits, this list is traversed and each file is closed and unlinked. It
seems to me that this mechanism is appropriate for temp files in
general, not just lock files. Thus, my proposal would be to extract
this logic into a separate module--tempfile.h, perhaps. Lock and
object files would share the tempfile implementation.

That is, both object and lock temp files would be stored in a linked
list, and all of these would be deleted at program exit.

I'm very enthused about this project--I think it has it all:

- Tangible benefits for the end-user
- Reduced complexity in the codebase
- Ambitious enough to be interesting
- Small enough to realistically be completed in a summer

Please let me know if this seems like it would make for an interesting
proposal, or if perhaps there is something I am overlooking. Any
feedback at all would be appreciated. Thank you!

- Brian Gesiak

[1] http://thread.gmane.org/gmane.comp.version-control.git/242891
[2] http://thread.gmane.org/gmane.comp.version-control.git/242893
[3] https://github.com/git/git/blob/v1.9.0/lockfile.c#L18
[4] https://github.com/git/git/blob/v1.9.0/lockfile.c#L143
[5] https://github.com/git/git/blob/v1.9.0/pack-write.c#L350