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Message-ID: <17B78BDF120BD411B70100500422FC6309E0C7@IIS000>
From: Bernard Dautrevaux <Dautrevaux AT microprocess DOT com>
To: "'Charles S. Wilson'" <cwilson AT ece DOT gatech DOT edu>,
        Robert Collins
	 <robert DOT collins AT itdomain DOT com DOT au>,
        cygwin AT sources DOT redhat DOT com
Subject: RE: DLL naming conventions
Date: Mon, 4 Sep 2000 17:27:54 +0200 
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> -----Original Message-----
> From: Charles S. Wilson [mailto:cwilson AT ece DOT gatech DOT edu]
> Sent: Monday, September 04, 2000 5:09 PM
> To: Robert Collins; cygwin AT sources DOT redhat DOT com
> Subject: Re: DLL naming conventions
> 
> 
	....

> 
> Here's the search order for DLL's when an AppPath key is set for the
> executable in the registry:
> 
> 1.The directories listed in the App Path registry key 
> 
> 2.The directory where the executable module for the current process is
> located. 
> 
> 3.The current directory. 
> 
> 4.The Windows system directory. The GetSystemDirectory function
> retrieves the path of this directory. 
> 
> 5.The Windows directory. The GetWindowsDirectory function 
> retrieves the
> path of this directory. 
> 
> 6.The directories listed in the PATH environment variable.
> 
> 
> See http://codeguru.earthweb.com/dll/AppPath.shtml
> 
> So, if all .exe's are installed using 'install.exe', and 
> install.exe is
> made smart enough to create an AppPath key for each one -- the problem
> is solved!
> 
> (sotto voce: ermmm...three minor problems:
> 
> 1. The AppPath entry must be in windows-format:
> C:\cygwin\bin;C:\cygwin\usr\local\bin  NOT /bin:/usr/local/bin.  What
> happens when you reinstall cygwin to a different location -- say
> D:\cygwin -- and change the mount points?
> 
> 2. The AppPath entry is keyed by the program name:
> 
> HKLM\Software\Microsoft\Windows\CurrentVersion\App Paths\foo.exe
>   default value is string   = "C:\cygwin\usr\local\bin\foo.exe"
>   string value named "Path" = "C:\cygwin\bin;C:\cygwin\usr\local\bin"
> 
> What if you have two foo.exe's -- one cygwin, and one mingw ?

Or cygwin find/native find ? Gonna crash the find feature of Explorer?

> 
> 3. It doesn't work if there is already a dll with the same 
> name, loaded
> into memory (for Win95, Win98, and WinNT; the following 
> analysis doesn't
> apply to Win98SE or W2K)
> 
> e.g. 
>   c:\cygwin\usr\local\bin\app1.exe
>     (app1.exe has AppPath key so that c:\cygwin\usr\bin is searched
> first)
>   c:\cygwin\usr\bin\my-dll.dll
> 
>   c:\mingw\usr\local\bin\app2.exe
>     (app2.exe has AppPath key so that c:\mingw\usr\bin is searched
> first)
>   c:\mingw\usr\bin\my-dll.dll
> 
> Run app1.exe -- fine, c:\cygwin\usr\bin\my-dll.dll gets loaded.
> Run app2.exe -- *will not load* c:\mingw\usr\bin\my-dll.dll 
> into memory.
> 
> This analysis extrapolated from description in:
> http://codeguru.earthweb.com/mfc/comments/6493.shtml
> 
> Maybe the problem isn't solved by AppPath, after all.
> 

This seems to say that DLLs are searched FIRST in memory, then on the disk
(at least on NT and 95/98)... That was what I seems to understand while
reading MSDN Library where they says that side-by-side libraries avoid this
preference given to already loaded libraries.

If this proves true, then the only solution would be to change the name of
the DLLs ;-(

Note that the in-memory problem is particularly important giving the fact
that a lot of windoze apps (cygwin or not) are usually long-lived especially
if they have a GUI. Thus if one starts a mingw GUI app that uses libpng.dll
(quite logical) then NO cygwin app using libpng will be able to run as it
will always try to use the mingw-libpng.dll in memory.

Does that mean that most ported unix apps were not interactive apps but
short-lived ones or that people are so sued to PCs crashing when trying to
do several things at once that they do not complain :-)

Cheers,

		Bernard

--------------------------------------------
Bernard Dautrevaux
Microprocess Ingenierie
97 bis, rue de Colombes
92400 COURBEVOIE
FRANCE
Tel:	+33 (0) 1 47 68 80 80
Fax:	+33 (0) 1 47 88 97 85
e-mail:	dautrevaux AT microprocess DOT com
		b DOT dautrevaux AT usa DOT net
-------------------------------------------- 

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