On Thu, Jan 22, 2015 at 11:54:49AM +0100, Michael Haggerty wrote:
> > +run_with_limited_open_files () {
> > + (ulimit -n 32 && "$@")
> > +}
>
> Regarding the choice of "32", I wonder what is the worst-case number of
> open file descriptors that are needed *before* counting the ones that
> are currently wasted on open loose-reference locks. On Linux it seems to
> be only 4 with my setup:
>
> $ (ulimit -n 3 && git update-ref --stdin </dev/null)
> bash: /dev/null: Too many open files
> $ (ulimit -n 4 && git update-ref --stdin </dev/null)
> $
>
> This number might depend a little bit on details of the repository, like
> whether config files import other config files. But as long as the
> "background" number of fds required is at least a few less than 32, then
> your number should be safe.
>
> Does anybody know of a platform where file descriptors are eaten up
> gluttonously by, for example, each shared library that is in use or
> something? That's the only think I can think of that could potentially
> make your choice of 32 problematic.
It's not just choice of platform. There could be inherited descriptors
in the environment (e.g., the test suite is being run by a shell that
keeps a pipe to CI server open, or something). And the test suite itself
uses several extra descriptors for hiding and showing output.
I think this is the sort of thing that we have to determine with a mix
of guessing and empiricism. 4 is almost certainly too low. 32 looks
"pretty big" in practice but not so big that it will make the test slow.
I think our best bet is probably to ship it and see if anybody reports
problems while the patch cooks. Then we can bump the number (or find a
new approach) as necessary.
-Peff
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