Re: [boost] RE: Re: DLL library (Was: Re: additional boost libraries?)

From: Florian Grafenberg (florian-grafenberg_at_[hidden])
Date: 2004-08-03 10:44:47

Hi boosters,

I developed a fairly simple prototype of a dll loader which mangles 
functions names automatically. But there are limitiations: you cannot 
call function which have template class parameters or return value, e.g. 
void test(std::string const &str) will not work. I do not get the 
mangling scheme used to decorate such a type, maybe someone knows a good 
source where I can look that up?!
For class mangling I use the string returned by type_info::name(), but 
that seems very hacky. Microsoft Visual C++ does not always return 
correct strings (e.g. typeid(int &).name() returns "int").

Sorry that I attached the source code to that mail as I know that only a 
few will look at it, but I don't have a homepage handy to upload it there.

- nico

> Vladimir Prus wrote:
>
>> Reece Dunn wrote:
>> >>I also wonder if it makes sense to sumbit just "dll" library, or some
>> >>additional plugin support need to be developed first.
>> >
>> > What sort of plugin support are you looking for? Do you mean something
>> > like COM/CORBA support or wrapper, e.g. something that can target both
>> > (and others like them) in one implementation?
>>
>> I'm not CORBA expert, but I think it's entirely different beast. To use
>> CORBA object you use stub generated from IDL, how it's related to 
>> plugins?
>> While there are some ways to find object dynamically, it's different
>> mechanism from shared libraries, isn't it?
>
>
> I am not sure how CORBA works. COM generally uses a different 
> mechanism to load COM objects via CoCreateInstance, although DirectX 
> exposes creation functions that circumvent this. I was thinking about 
> being able to use COM/CORBA as a platform for object lifetime and dll 
> lifetime management (as well as things like interface extension, etc.).
>
>> I though more about at least some kind of map<string, BasePlugin*> 
>> which is
>> updated automatically when you load new DLLs.
>
>
> So the dll implements some function:
>
>   __declspec(dllexport) BasePlugin * GetMyPlugin();
>
> so you can do something like:
>
>   void load_plugins( map< string, BasePlugin * > & pi )
>   {
>      for( map< string, BasePlugin * >::iterator i = pi.begin(); i != 
> pi.end(); ++i )
>      {
>         boost::dll plugin(( *i ).first );
>         ( *i ).second = plugin.import< ... >( "GetMyPlugin" );
>      }
>   }
>
> It is possible to keep the DLL in memory until all instances of a 
> class (or set of classes) by incrementing/decrementing a global object 
> count variable on construction/deconstruction as is done when using 
> COM. You then check this variable in the DllCanUnload function.
>
> You may need some reference counting mechanism to keep the plugin 
> alive, but this is not necessary if you load all plugins on startup 
> and release them at the end of the run.
>
> It should be possible to implement these facilities in a library, e.g.:
>
> class object_counter
> {
>   private:
>      static int objectCount = 0;
>   public:
>      inline int get_object_count(){ return( objectCount ); }
>   public:
>      inline object_counter(){ ++objectCount; } // make MT aware
>      inline ~object_counter(){ --objectCount; } // make MT aware
> };
>
> class reference_counter
> {
>   private:
>      int refCount;
>   public:
>      inline void add_ref(){ ++refCount; } // make MT aware
>      inline void dec_ref()
>      {
>         if( --refCount == 0 ) // make MT aware
>         {
>            delete this;
>         }
>      }
>   public:
>      inline reference_counter( int rc ): refCount( rc ){}
>      inline ~reference_counter(){}
> };
>
> allowing:
>
> class plugin: public object_counter, public reference_counter, public 
> BasePlugin
> {
>   // ...
> };
>
> __declspec(dllexport) BOOL DllCanUnload()
> {
>   return( object_counter::get_object_count() == 0 );
> }
>
> I'm not sure what the Linux equivalent would be.
>
> Regards,
> Reece
>
> _________________________________________________________________
> Want to block unwanted pop-ups? Download the free MSN Toolbar now!  
> http://toolbar.msn.co.uk/
>
> _______________________________________________
> Unsubscribe & other changes: 
> http://lists.boost.org/mailman/listinfo.cgi/boost
>
>

*****************************************************************************
**                                                                         **
** WARNING:  This email contains an attachment of a very suspicious type.  **
** You are urged NOT to open this attachment unless you are absolutely     **
** sure it is legitmate.  Opening this attachment may cause irreparable    **
** damage to your computer and your files.  If you have any questions      **
** about the validity of this message, PLEASE SEEK HELP BEFORE OPENING IT. **
**                                                                         **
** This warning was added by the IU Computer Science Dept. mail scanner.   **
*****************************************************************************