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X-Authentication-Warning: slinky.cs.nyu.edu: pechtcha owned process doing -bs
Date: Tue, 10 Dec 2002 11:55:09 -0500 (EST)
From: Igor Pechtchanski <pechtcha AT cs DOT nyu DOT edu>
Reply-To: cygwin AT cygwin DOT com
To: cygwin AT cygwin DOT com
Subject: Re: cygwin 1.3.17-1 gethostbyname() leak
In-Reply-To: <20021210173645.D26891@cygbert.vinschen.de>
Message-ID: <Pine.GSO.4.44.0212101153150.12239-100000@slinky.cs.nyu.edu>
Importance: Normal
MIME-Version: 1.0
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On Tue, 10 Dec 2002, Corinna Vinschen wrote:

> On Tue, Dec 10, 2002 at 10:36:04AM -0500, Igor Pechtchanski wrote:
> > On Tue, 10 Dec 2002, Noel Gordon wrote:
> >
> > > Anyone else confirm that the following program compiled under
> > > gcc 3.2, cygwin 1.3.17-1, on Win2k leaks memory?
>
> Confirmed.  I found the missing free().
>
> > >From http://www.opengroup.org/onlinepubs/007904975/functions/gethostbyaddr.html :
> >
> >       The gethostbyaddr() and gethostbyname() functions *may* return
> >       pointers to static data, which may be overwritten by subsequent
> >       calls to any of these functions.
> >
> > The "may" above (emphasis is mine) means that the implementation is free
> > to malloc a data structure and require the user to free it.  Since you
> > don't free the returned data structure in your program, it's quite
> > possible that there's a leak.  Also, Cygwin uses the gethostbyname from
> > wsock32.dll, which may have different implementations on different
> > systems.  Thus, your best bet is to look up gethostbyname on MSDN for
> > implementation details.
>
> Ignore MSDN.  It's using an internal per-thread buffer which collides with
> the fork/exec mechanism of Cygwin so Cygwin duplicates the buffer to
> another Cygwin-thread specific allocated buffer.  The deallocation of
> the buffer is Cygwin internal so hands off please.
>
> Thanks for the report, I've checked in a patch,
> Corinna

Umm, note to self: always browse *all* of the relevant code before
expressing opinions on the cygwin list!

Apologies to all for the misinformation.  I've found the gethostbyname
entry in autoload.cc and did not look further.  Had I paid more attention,
I would have noticed the cygwin_gethostbyname() in net.cc, which is the
actual implementation and does what Corinna said.
	Igor
-- 
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     |,4-  ) )-,_. ,\ (  `'-'		Igor Pechtchanski
    '---''(_/--'  `-'\_) fL	a.k.a JaguaR-R-R-r-r-r-.-.-.  Meow!

"Water molecules expand as they grow warmer" (C) Popular Science, Oct'02, p.51


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