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From: "Tom R.Hageman" <tom@basil.icce.rug.nl>
Date: Wed, 12 Jul 95 18:50:05 +0200
To: rp2y@methi.ndim.edrc.cmu.edu
Subject: Re: putenv in postmaster.c
Cc: postgres@postgres.Berkeley.EDU,
        Shreeniwas N Sapre	<sns@asterix.cs.unipune.ernet.in>
References: <199507101710.KAA06819@nobozo.CS.Berkeley.EDU>
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Resent-Date: Thu, 13 Jul 95 09:13:17 -0700
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Robert Patrick <rp2y@methi.ndim.edrc.cmu.edu> wrote:
> [Shreeniwas N Sapre <sns@asterix.cs.unipune.ernet.in> wrote:]
> > The use of putenv in postmaster.c (sample below) has crashed
> > postmaster on our system (DGUX 5.4R2.10). The symptom is its inability
> > to find "template1" after servicing the first 2 or 3 requests. My
> > diagnosis is the use of envEntry ( which is on stack) for putenv
> > causing corrupted environment entries, as putenv keeps a pointer to
> > the string and not a copy of the string. This problem surfaced after
> > we made a few changes (unrelated to this problem) to postmaster. We
> > have made envEntry as "static" as a solution.
> >
[code sample munched]
>
> First, I'm confused by the code that you posted, this obviously isn't
> right since the memory allocated for envEntry is allocated on the
> stack when this function is called and released when the function
> returns.  I am assuming that this is the "bad" example.
>
> Second, I'm not sure where you got this code because both Postgres V4.2
> and Postgres95 actually declare envEntry as an array of pointers and
> call calloc() to allocate the memory (which is probably a cleaner
> solution that using a "static" array of character arrays).
>
> BackendStartup looks like this in Postgres V4.2:
>
> BackendStartup(packet, port)
> ...
> {
> ...
>     char	*envEntry[4];
>
>
>     for (i = 0; i < 4; ++i) {
> 	envEntry[i] = calloc(2 * ARGV_SIZE, 1);
>     }
>     sprintf(envEntry[0], "POSTPORT=%d", PostPortName);
>     putenv(envEntry[0]);
>
> ...
> }

Well, I've got the original postgres 4.2 lying around and it indeed uses the  
method as described by the first poster.  There has been a patch (I think) by  
aoki that changed this to use calloc()ed strings.

The disadvantage of the new method, at least the way it is implemented now,  
is that it introduces a memory leak.  Which is rather a nuisance in a  
potentially never-ending process like the postmaster. (but then, I'm sure it  
is not the only one... <wry grin>)

--
__/__/__/__/  Tom Hageman  <tom@basil.icce.rug.nl>  [NeXTmail/Mime OK]
  __/ __/_/         IC Group  <tom@icgned.nl> (work)
 __/__/__/          "...to baldly go where no one has gone before."
__/  _/_/                                             -- star trek TNG

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