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

[Brian Gesiak <modocache@gmail.com>]

> Currently the linked list of lockfiles only grows, never shrinks.  Once
> an object has been linked into the list, there is no way to remove it
> again even after the lock has been released.  So if a lock needs to be
> created dynamically at a random place in the code, its memory is
> unavoidably leaked.

Ah yes, I see. I think a good example is
config.git_config_set_multivar_in_file, which even contains a comment
detailing the problem: "Since lockfile.c keeps a linked list of all
created lock_file structures, it isn't safe to free(lock).  It's
better to just leave it hanging around."

> But I have a feeling that if we want to use a similar mechanism to
> handle all temporary files (of which there can be more), then it would
> be a good idea to lift this limitation.  It will require some care,
> though, to make sure that record removal is done in a way that is
> threadsafe and safe in the event of all expected kinds of process death.

It sounds like a threadsafe linked-list with an interface to manually
remove elements from the list is the solution here; does that sound
reasonable? Ensuring thread safety without sacrificing readability is
probably more difficult than it sounds, but I don't think it's
impossible.

I'll add some more details on this to my proposal[1]. Thank you!

- Brian Gesiak

[1] https://www.google-melange.com/gsoc/proposal/review/student/google/gsoc2014/modocache/5629499534213120