Vorbis dev - Oct 2001 - win32sdk shared memory issue -- proposed change of code

It was recently brought to my attention by "Ram'on Garc'ia
Fern'andez <ramon@jl1.quim.ucm.es>"
that there is yet an even simpler solution to the issue of cross-DLL access of
variables in the data segment.

Although a variable may be exported either from the module definition file, or
explicitly
via _cdeclspec(dllexport) -- unlike procedures (functions), it is mandatory for
a DLL
client to access that variable via _cdeclspec(dllimport).

It is unnecessary to allocate dynamic memory and then copy pointers 
to that allocated memory, as is done with the vorbis/win32/src/shmmap.h and 
vorbis/win32/src/shmmap_c.h stuff.

In otherwords, we've come full circle -- it looks like the linking paradigm
in Windows
is closer to what would be expected when developing under UNIX, after all...

...well -- almost, as mentioned, the "_cdeclspec(dllimport)" attribute
is required, such that
a modification of "vorbis/lib/registry.h" is required which would look
like:

#if defined(_MSC_VER) && defined(DLL_IMPORT)
# define EXTERN _declspec(dllimport) extern
#else
# define EXTERN extern
#endif

EXTERN vorbis_func_time      *_time_P[];
EXTERN vorbis_func_floor     *_floor_P[];
EXTERN vorbis_func_residue   *_residue_P[];
EXTERN vorbis_func_mapping   *_mapping_P[];

I realize the aesthetics of having "EXTERN" instead of
"extern" may be an issue on
non-win32 platforms, (although in this case it would still preprocess out to
"extern")
so I thought I'd present the proposed change to the list before commiting to
CVS...

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On 17 Oct 2001, you wrote in internal.mail.vorbis-dev:
> I realize the aesthetics of having "EXTERN" instead of
"extern" may be
> an issue on non-win32 platforms, (although in this case it would still
> preprocess out to "extern") so I thought I'd present the
proposed
> change to the list before commiting to CVS... 
BTW, some remarks about the win32 batch files:

You should replace "exit"s by a "goto" to the end of the
file, because
using "exit" closes the console - it does *not* return to the calling
batch
file (as you expect in mkmak.bat when calling mfmacro.bat). One also 
doesn't get a chance of seeing the error messages before exiting when there 
are some - the console just closes without showing them. "Sleep"
doesn't
exist on my system either (Clean Win2000sp2/msvc6sp5pp install).

And before "echo Generating makefiles, please wait..." in mkmak.bat
the
user should install the macro file by opening msdev, going to Tools -> Add-
ins and Macro Files and ticking the checkbox for "oggvorbis". Then the
SDKHOME needs to be set before running the other batch files.

Hope this helps,

Matthijs

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On 2001-10-17 at 20:00:38 Chris Wolf wrote:

CW> #if defined(_MSC_VER) && defined(DLL_IMPORT)
CW> # define EXTERN _declspec(dllimport) extern
CW> #else
CW> # define EXTERN extern
CW> #endif

CW> EXTERN vorbis_func_time      *_time_P[];
CW> EXTERN vorbis_func_floor     *_floor_P[];
CW> EXTERN vorbis_func_residue   *_residue_P[];
CW> EXTERN vorbis_func_mapping   *_mapping_P[];

I propose changing that to:

#if defined(_WIN32) && defined(VORBISDLL_IMPORT)
# define EXTERN __declspec(dllimport) extern
#else
# define EXTERN extern
#endif

EXTERN vorbis_func_time      *_time_P[];
EXTERN vorbis_func_floor     *_floor_P[];
EXTERN vorbis_func_residue   *_residue_P[];
EXTERN vorbis_func_mapping   *_mapping_P[];

The defined(_WIN32) is because MSVC is not the only Win32 compiler,
and almost all other Win32 compilers grok the __declspec stuff anyway,
for compatibility reasons. (Btw, according to the Microsoft docs, it's
__declspec, not _declspec.)

The defined(VORBISDLL_IMPORT) is because DLL_IMPORT is simply too
generic. There might be more imported DLLs in a Win32 project. ;-)

Cheers,
- --
Dimitry Andric <dim@xs4all.nl>
PGP Key: http://www.xs4all.nl/~dim/dim.asc
Fingerprint: 7AB462D2CE35FC6D42394FCDB05EA30A2E2096A3
Lbh ner abj va ivbyngvba bs gur QZPN

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