Date: Fri, 7 Aug 1998 10:37:26 -0700 (PDT) From: Archie Cobbs <archie@whistle.com> To: wollman@khavrinen.lcs.mit.edu (Garrett Wollman) Cc: freebsd-current@FreeBSD.ORG, bde@zeta.org.au, dg@root.com Subject: Re: memory leaks in libc Message-ID: <199808071737.KAA29957@bubba.whistle.com> In-Reply-To: <199808071721.NAA20680@khavrinen.lcs.mit.edu> from Garrett Wollman at "Aug 7, 98 01:21:21 pm"
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Garrett Wollman writes:
> No, you've missed the point entirely. *Any program which does enough
> playing around with the environment to be harmed by this memory leak
> is using a totally inappropriate interface.*
I disagree with that statement! And I base my disagreement not on
conjecture but on experience.
Here's a REAL example.. suppose you have a program which runs
as a daemon, and it's job is to display the time on some display.
The display of the time is generated via strftime(3). The device
this daemon is running on allows the timezone to be configured.
In order to display the time in the correct timezone, every so
often (every 30 seconds or so) this deamon must make sure that
strftime() knows about the *currently set* timezone, not the timezone
that was set when the daemon started (which could be arbitrarily
long ago in the past).
How can it possibly do this? The only way to get strftime() to
acknowledge a change in timezone is to do something like this:
unsetenv("TZ");
tzset();
setenv("TZ", "/etc/localtime", 1);
tzset();
(if you don't believe me then read the source for tzset() et. al.)
Guess what? Every 30 seconds this deamon is malloc()'ing a new
malloc block. Your supposedly reliable device will crash in a matter
of days when it exhausts all available memory because of the memory leak.
There's nothing "totally inappropriate" about what the daemon is
doing -- in fact, using setenv() is the only way to do what it
wants to do, ie., get libc to acknowledge a timezone change.
My point? I agree with you that a program that implements a relational
database using setenv()/getenv() as a backend would be "totally
inappropriate". What I'm saying is that not every program which
suffers from the setenv() memory leak is doing something "totally
inappropriate".
-Archie
___________________________________________________________________________
Archie Cobbs * Whistle Communications, Inc. * http://www.whistle.com
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