April 19, 2008
Robert Fraser wrote:

> Frank Benoit wrote:
>> [...]
> 
> I really wish DDL was still alive, or something similar. That had the right idea and would have solved many of the issues D has with traditional dynamic libraries.

On Windows at least - turns out *nix .so's can do most of what was ever planned for DDL in any case. Not that I think DDL is dead dead, just not gaining features at a very quick pace.

-- 
Lars Ivar Igesund
blog at http://larsivi.net
DSource, #d.tango & #D: larsivi
Dancing the Tango
April 19, 2008
Robert Fraser schrieb:
> Frank Benoit wrote:
>> [...]
> 
> I really wish DDL was still alive, or something similar. That had the right idea and would have solved many of the issues D has with traditional dynamic libraries.

I really wish, i would understand the problems (or how it works)
On windows, walter says it works.
On linux, e-t172 says it works.

Can you give an example for problems?
April 20, 2008
e-t172 schrieb:
> Frank Benoit a écrit :
>> Can "new MyClass" be called?
> 
> Yes, why not?

In my understanding, if you have an object reference, a virtual call can be done with it. The reference points you to the vtable, and that to the methods address.

What about static, non-virtual and ctor calls?
- static & ctor: no obj ref, hence no access to vtable
- final & package methods: probably not in the vtable
- public static member vars: access over global address
I don't know, this is just a guess.

If the .dll/.so is statically linked the linker does the magic.

But if you load the .so/.dll dynamically, the address needs to be loaded via dlsym() or getProcAddress()?

This is why i think the ctor might be problematic.




April 20, 2008
The problem with windows DLLs is that they don't support partial linking ( or how it was called ). That is, you can't have undefined symbols in a DLL. What does it mean for an average D program? Each DLL will have to contain all symbols that it imports (uses). So multiple std-libs, multiple ClassInfos for the same classes, multiple globals. Unless these are somehow magically matched at runtime, you'll be in serious trouble. E.g. casting an object returned from a DLL to Object will return null. The ClassInfo in DLL and the host will be different objects, thus failing at the cast. This may be worked around (to some extent), e.g. by walking the rtti manually and comparing class names, doing casting thru void* pointers...

Still, exceptions bork for the same reason. Whatever is being thrown, it's converted to the type being caught, thus exception handling will fail really badly across binary boundaries. And IIRC, really badly == instant crash at an exception being thrown inside a DLL.

More info on DLLs and D: http://dsource.org/forums/viewtopic.php?t=677 it's quite old but describes the problems and highlights why DDL was conceived.

DDL on the other hand, provides pretty much the functionality that .SO on Unix do (plus introspection of the loaded modules), thus allowing partial linking. Everything 'just works' since the undefined symbols will be taken from the host application, thus globals, typeinfo and whatnot will be shared between the host and the plugins.

DDL is not being actively maintained because Eric is currently busy with other stuff, mainly due to rand() real life events.
Last time I checked, DDL compiled with Tango and the basic examples worked.

DDL only works with DMD-win though. As for GDC on MSYS, someone might try binding EDLL: http://edll.sourceforge.net/, porting it to work with DDL's interface or helping Gregor's WinELF: http://svn.berlios.de/svnroot/repos/crosslibc/other/winelf/

Hope this info is useful :) Cheers!


-- 
Tomasz Stachowiak
http://h3.team0xf.com/
h3/h3r3tic on #D freenode
April 20, 2008
Frank Benoit wrote:
> Walter Bright schrieb:
>> Frank Benoit wrote:
>>> - Why isn't it possible to call "new MyClass" instead of "getMyClass"?
>>
>> ??
> 
> In the example a getMyClass is used. So i thought it might not be possible to call "new MyClass" directly?

The idea is to be careful which heap MyClass is allocated on - the DLL's or the caller's?
April 20, 2008
Frank Benoit wrote:
> - final & package methods: probably not in the vtable

About "package"... I noticed this too and had to change stuff o public. What does "package" have to do with the vtable; it means that the symbol is only accessible from within the package. So if a method is package-protected, any other module in the same package should be able to override it.
April 20, 2008
On Sun, 20 Apr 2008 01:50:46 +0200, Frank Benoit <keinfarbton@googlemail.com> wrote:

There is a summary of issues with DLLs posted by the DDL's creator to
the wiki long time ago:
http://www.prowiki.org/wiki4d/wiki.cgi?BestPractices/DLL
AFAIK, all those issues still remain unresolved.
April 20, 2008
Tom S schrieb:
> More info on DLLs and D: http://dsource.org/forums/viewtopic.php?t=677 it's quite old but describes the problems and highlights why DDL was conceived.

I think you did mean this one?
http://dsource.org/forums/viewtopic.php?t=959
April 20, 2008
Frank Benoit wrote:
> Tom S schrieb:
>> More info on DLLs and D: http://dsource.org/forums/viewtopic.php?t=677 it's quite old but describes the problems and highlights why DDL was conceived.
> 
> I think you did mean this one?
> http://dsource.org/forums/viewtopic.php?t=959

This one is a continuation of the other thread's DLL/DDL ramblings :>

-- 
Tomasz Stachowiak
http://h3.team0xf.com/
h3/h3r3tic on #D freenode
April 25, 2008
Tom S wrote:
> 
> DDL on the other hand, provides pretty much the functionality that .SO on Unix do (plus introspection of the loaded modules), thus allowing partial linking. Everything 'just works' since the undefined symbols will be taken from the host application, thus globals, typeinfo and whatnot will be shared between the host and the plugins.
> 
> DDL is not being actively maintained because Eric is currently busy with other stuff, mainly due to rand() real life events.
> Last time I checked, DDL compiled with Tango and the basic examples worked.
> 

Yup. Due to the nature of DLL's, D-to-D shared libraries are never going to work right (unless one restricts the API to C-level constructs only, ie, no classes, no exceptions, etc.).
That's why a project such as DDL is so important, and it's a shame that Walter does not realize how beneficial such technology would be for D. Anyone who has used libraries with Java or C# (or interpreted high-level languages) knows how comfortable it is not having to worry about any of such issues, and still have the full power of the language available across libraries.

-- 
Bruno Medeiros - Software Developer, MSc. in CS/E graduate
http://www.prowiki.org/wiki4d/wiki.cgi?BrunoMedeiros#D
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