From: Junio C Hamano <gitster@pobox•com>
To: Jeff King <peff@peff•net>
Cc: Joey Hess <joey@kitenet•net>, git@vger•kernel.org
Subject: Re: RLIMIT_NOFILE fallback
Date: Wed, 18 Dec 2013 12:18:21 -0800 [thread overview]
Message-ID: <xmqqlhzhhq0i.fsf@gitster.dls.corp.google.com> (raw)
In-Reply-To: <xmqq61qmhrb3.fsf@gitster.dls.corp.google.com> (Junio C. Hamano's message of "Wed, 18 Dec 2013 11:50:24 -0800")
Junio C Hamano <gitster@pobox•com> writes:
> Jeff King <peff@peff•net> writes:
>
>> That is, does sysconf actually work on such a system (or does it need a
>> similar run-time fallback)? And either way, we should try falling back
>> to OPEN_MAX rather than 1 if we have it.
>
> Interesting.
>
>> As far as the warning, I am not sure I see a point. The user does not
>> have any useful recourse, and git should continue to operate as normal.
>> Having every single git invocation print "by the way, RLIMIT_NOFILE does
>> not work on your system" seems like it would get annoying.
>
> Very true. That makes the resulting function look like this:
>
>
> -------------------------------- 8< ------------------------------
>
> static unsigned int get_max_fd_limit(void)
> {
> #ifdef RLIMIT_NOFILE
> struct rlimit lim;
>
> if (!getrlimit(RLIMIT_NOFILE, &lim))
> return lim.rlim_cur;
> #endif
>
> #if defined(_SC_OPEN_MAX)
> {
> long sc_open_max = sysconf(_SC_OPEN_MAX);
> if (0 < sc_open_max)
> return sc_open_max;
> }
err, here we need
#endif /* defined(_SC_OPEN_MAX) */
to truly implement the structure "try all the available functions,
and then fall back to OPEN_MAX".
>
> #if defined(OPEN_MAX)
> return OPEN_MAX;
> #else
> return 1; /* see the caller ;-) */
> #endif
> }
>
> -------------------------------- >8 ------------------------------
>
>
> But the sysconf part makes me wonder; here is what we see in
> http://pubs.opengroup.org/onlinepubs/9699919799/functions/sysconf.html
>
> If name is an invalid value, sysconf() shall return -1 and set errno
> to indicate the error. If the variable corresponding to name is
> described in <limits.h> as a maximum or minimum value and the
> variable has no limit, sysconf() shall return -1 without changing
> the value of errno. Note that indefinite limits do not imply
> infinite limits; see <limits.h>.
>
> For a broken system (like RLIMIT_NOFILE defined for the compiler,
> but the actual call returns a bogus error), the compiler may see the
> _SC_OPEN_MAX defined, while sysconf() may say "I've never heard of
> such a name" and return -1, or the system, whether broken or not,
> may want to say "Unlimited" and return -1. The caller takes
> anything unreasonable as a positive value capped to 25 or something,
> so there isn't a real harm if we returned a bogus value from here,
> but I am not sure what the safe default behaviour of this function
> should be to help such a broken system while not harming systems
> that are functioning correctly.
next prev parent reply other threads:[~2013-12-18 20:18 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-18 17:14 RLIMIT_NOFILE fallback Joey Hess
2013-12-18 18:00 ` Junio C Hamano
2013-12-18 18:41 ` Joey Hess
2013-12-18 19:17 ` Jeff King
2013-12-18 19:50 ` Junio C Hamano
2013-12-18 20:18 ` Junio C Hamano [this message]
2013-12-18 21:28 ` Jeff King
2013-12-18 21:37 ` Junio C Hamano
2013-12-18 21:40 ` Jeff King
2013-12-18 22:59 ` Junio C Hamano
2013-12-19 0:15 ` Jeff King
2013-12-19 17:30 ` Torsten Bögershausen
2013-12-19 17:39 ` Junio C Hamano
2013-12-20 9:12 ` Jeff King
2013-12-20 14:43 ` Torsten Bögershausen
2013-12-18 20:03 ` Joey Hess
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