Date: Sat, 7 Jul 2007 21:03:59 -0500 (CDT)
From: "Sean C. Farley" <scf@FreeBSD.org>
To: Andrey Chernov <ache@nagual.pp.ru>
Cc: freebsd-current <freebsd-current@FreeBSD.org>, Robert Watson <rwatson@FreeBSD.org>, Michal Mertl <mime@traveller.cz>
Subject: Re: Environment handling broken in /bin/sh with changes to {get,set,put}env()
Message-ID: <20070707205410.B14065@thor.farley.org>
In-Reply-To: <20070707191835.GA4368@nagual.pp.ru>
References: <20070704180000.GA34042@nagual.pp.ru> <20070704144159.X77978@thor.farley.org> <20070704195939.GA35302@nagual.pp.ru> <20070704235630.GA42227@nagual.pp.ru> <20070704215154.O77978@thor.farley.org> <20070705115816.GA50506@nagual.pp.ru> <20070705105922.F98700@thor.farley.org> <20070707130859.GA96605@nagual.pp.ru> <20070707131359.GB96605@nagual.pp.ru> <20070707133102.C14065@thor.farley.org> <20070707191835.GA4368@nagual.pp.ru>
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On Sat, 7 Jul 2007, Andrey Chernov wrote:
> On Sat, Jul 07, 2007 at 01:51:11PM -0500, Sean C. Farley wrote:
>> I agree that it would be faster for a subset of an existing environ.
>> On the other hand, in the case of emptying the environment, my method
>> would be faster since no deallocation, allocation nor setenv() calls
>> would be called assuming putenv() was not used. I could try a few
>> tests to see what is faster in which case, but I do not think environ
>> changes happen often enough to make speed a factor.
>
> Well, lets go with that.
I ran the tests out of curiosity. All code is here[1]. The dropping
was effectively freeing envVars and the environ that getenv.c creates
for the program. All other counters were set to zero.
The first test (timing-clear.c) cleared the environment by swapping two
char ** arrays containing a single NULL pointer. 500000 iterations.
x drop/clear-timings.txt
+ keep/clear-timings.txt
N Min Max Median Avg Stddev
x 50 1.634899 1.672082 1.656838 1.6567984 0.0093033009
+ 50 1.326203 1.348855 1.3296575 1.3323876 0.0062632107
Difference at 95.0% confidence
-0.324411 +/- 0.00314674
-19.5806% +/- 0.189929%
(Student's t, pooled s = 0.0079303)
The second test (timing-merge.c) swapped two duplicates of my
environment over 5000 iterations.
x drop/merge-timings.txt
+ keep/merge-timings.txt
N Min Max Median Avg Stddev
x 50 1.337052 1.406142 1.3663635 1.3634524 0.015210835
+ 50 0.889559 0.913354 0.8943785 0.89644634 0.0056274351
Difference at 95.0% confidence
-0.467006 +/- 0.00455057
-34.2517% +/- 0.333753%
(Student's t, pooled s = 0.0114682)
Surprisingly, keeping the pointers saved time even if calling setenv().
Sean
1. http://www.farley.org/freebsd/tmp/setenv/clearenv/
--
scf@FreeBSD.org
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