This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: [RFC] Make getenv O(1)
- From: OndÅej BÃlka <neleai at seznam dot cz>
- To: Alexander Monakov <amonakov at ispras dot ru>
- Cc: Florian Weimer <fweimer at redhat dot com>, Rich Felker <dalias at aerifal dot cx>, libc-alpha at sourceware dot org
- Date: Fri, 18 Oct 2013 16:07:05 +0200
- Subject: Re: [RFC] Make getenv O(1)
- Authentication-results: sourceware.org; auth=none
- References: <20131014155229 dot GA25159 at domone dot podge> <20131014165411 dot GZ20515 at brightrain dot aerifal dot cx> <20131014172852 dot GA26005 at domone dot podge> <52611F60 dot 3080700 at redhat dot com> <20131018124013 dot GA15803 at domone dot podge> <alpine dot LNX dot 2 dot 00 dot 1310181656380 dot 3212 at monopod dot intra dot ispras dot ru> <20131018132604 dot GA16445 at domone dot podge> <alpine dot LNX dot 2 dot 00 dot 1310181744060 dot 3212 at monopod dot intra dot ispras dot ru>
On Fri, Oct 18, 2013 at 05:46:57PM +0400, Alexander Monakov wrote:
> On Fri, 18 Oct 2013, OndÅej BÃlka wrote:
> > You could argue that this does not help when likely case is that
> > variable is not defined. For that I would need posix say that changing
> > variable name via environ pointers is illegal.
>
> Indeed; I would also ask if such functions are allowed to query interesting
> environment variables once on first call and then cache the result (similar to
> how the dynamic linker stashes initial LD_LIBRARY_PATH on the side and calls
> to dlopen do not check the environment again).
>
> Alexander
This could be done by following macro with global renaming of
getenv->GETENV.
Also do we support in libc setenv to change behaviour?
#define GETENV(x) ({ \
static char *__ret; \
static int __cached; \
if (__builtin_constant_p (x) && !__cached) \
{ \
__ret = getenv (x); \
__cached = 1; \
} \
__builtin_constant_p (x) ? __ret : getenv (x);})