[PATCH 0/5] Avoid file descriptor exhaustion in ref_transaction_commit()

[Michael Haggerty <mhagger@alum.mit.edu>]

In ref_transaction_commit(), close the reference lockfiles immediately
to avoid keeping too many file descriptors open at a time. This is
pretty easy, because in the first loop (where we create the locks) we
already know what, if anything, has to be written into the lockfile.
So write it and close the lockfile immediately. In the second loop,
rename the lockfiles for reference updates into place, and in the
cleanup loop, unlock any references that are still locked (i.e., those
that were only being verified or deleted).

I think this is a cleaner solution than Stefan's approach [1] of
closing and reopening fds based on an estimate of how many fds we can
afford to waste--we only need a single file descriptor at a time, and
we never have to close then reopen a lockfile. But it is a bit more
intrusive, so it might still be preferable to use Stefan's approach
for release 2.4.0, if indeed any fix for this problem is still being
considered for that release.

This patch series applies on top of Stefan's

    c1f0ca9 refs.c: remove lock_fd from struct ref_lock (2015-04-16)

and it fixes two tests that Stefan introduced earlier in that series.

It is also available from my GitHub account:

    https://github.com/mhagger/git branch close-ref-locks-promptly

Michael

[1] http://article.gmane.org/gmane.comp.version-control.git/267548

Michael Haggerty (5):
  write_ref_to_lockfile(): new function, extracted from write_ref_sha1()
  commit_ref_update(): new function, extracted from write_ref_sha1()
  write_ref_sha1(): inline function at callers
  ref_transaction_commit(): remove the local flags variables
  ref_transaction_commit(): only keep one lockfile open at a time

 refs.c                | 107 ++++++++++++++++++++++++++++++++++----------------
 t/t1400-update-ref.sh |   4 +-
 2 files changed, 75 insertions(+), 36 deletions(-)

-- 
2.1.4