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Re: Environment handling broken in /bin/sh with changes to {get,set,put}env()



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/
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