[vorbis-dev] Problems trying to run the examples in windows v orbis sdk

[Chris Wolf]

On 9/5/2001 at 9:45 AM Chris Parsons wrote:

>> On 9/4/2001 at 6:00 PM Pablos-Sanchez, Rolando wrote:
>> 
>> >I have compiled the example 'encoder_example.c' just to start, and it
>> >compiles, but I got a error in the following line just at the
>beginning: 
>> >vorbis_encode_init(&vi,2,44100, -1, 128000, -1);
>> >The error is more or less: The instruction at '0xaddresss' referenced
>> >memory at '0xaddress'. The memory could not be "read".
>> 
>> The work around for this problem is to include vorbisenc.c in the vorbis
>DLL and not have a
>> separate, stand alone vorbisenc.dll.  If you do this, then this problem
>disappears.  Obviously,
>> since the vorbisenc code is quite large, and a lot of applications will
>only be decoding, this
>> is not a permenent solution.
>> 
>> This may have to do with how global data is treated in DLLs, which is
>that
>each client gets a 
>> fresh instance of the global data.  The problem seems to be accessing
>_time_P accross DLLs
>> (vorbisenc.dll accessing _time_P in vorbis.dll)  I'm thinking of trying a
>named data segment.
>
>
>That is exactly what the case is.  There is only a couple of ways to savely
>access global data across DLL's in Windows, probably the safest is to use
>CreateFileMapping() with a named memory space.  This way if the space was
>already created by a previous instance of the DLL it will open that space
>and not create a new one.  It used to be possible to pass global pointers
>across DLL's in Windows 3.x and to some extent with Win 9x, but it's more
>or
>less down right illegal in Win NT x.  It is legal however for a memory
>space
>allocated with GlobalAlloc to be passed to the calling application (or DLL)
>by handle.

Isn't it true that if you bracket global definitions with
#pragma data_seg(".some_name")
...
#pragma data_seg()

...that those globals become sharable a' la 3.x DLL's?  In any case, I tried it and it didn't help.

>From the debugger, I can access the address of _time_P, which is a global
inside vorbis.dll (I also have it exported in the module definition file)  I can even access the first element
of this pointer array, but when a try to dereference one of the function pointers, it blows up. 

Here's what I tried  (vorbisenc.c):

  /* time backend settings */
  for(i=0;i<ci->times;i++)
  {
      int vit = ci->time_type[i];
      vorbis_func_time *data = _time_P[vit];                                  // this succeeds

 //    void *(*copy_info)(vorbis_info_time *) = _time_P[vit];              // access violation
 //    void *(*copy_info)(vorbis_info_time *) = data->copy_info;        // access violation
//     void *(*copy_info)(vorbis_info_time *) = time0_copy_info;       // this succeeds
//     void *(*copy_info)(vorbis_info_time *) = time0_exportbundle.copy_info; // this succeeds

      ci->time_param[i] = copy_info(cs->time_param[i]);
    /*
    ci->time_param[i]=_time_P[ci->time_type[i]]->
      copy_info(cs->time_param[i]);
      */
  }

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