It's not just efficiency, it can actually cause errors.

I found , very similar.

On Mon, Dec 16, 2013 at 12:01 PM, Greg Hudson via RT <> wrote:
The OPENCLOSE flag is intended to be a matter of optimization, not
correctness.  Another thread using the already-open file shouldn't
generally be a problem; it will just be a little faster.  Are you seeing
a more severe issue than this?

(I can think of a scenario where there are two overlapping
krb5_cc_retrieve_cred_seqs running in different threads, and when the
first one finishes, it turns the OPENCLOSE flag back on, causing the
other thread to run less efficiently.  But I still don't see that causing
a user-visible problem, just an efficiency issue.)