Daniel Keep wrote:
grauzone wrote:
John Reimer wrote:
ddl does not work for memory sharing like normal dll's, where multiple
applications have access to a single dll at runtime. It appears that
such support would be quite difficult to implement and moves in the
direction of operating system features.
Couldn't this be achieved by simply mmap()-ing the file contents into
memory? mmap() normally shared the memory pages with other processes.
I'm sure users of DDL would love for you to submit a patch. :)
Of course, this wouldn't work if the code both isn't position
independent, and needs to be relocated to a different base address. But
that's also the case with operating system supported dynamic shared
objects.
It does do runtime linking, however, which is extremely useful for
certain situations... specifically any sort of application that needs
a plugin architecture for D (ie.. it can link with libraries and
object files at runtime) that is gc and exception friendly.
I never understood why this is needed. Can't they simply compile the
plugins into the main program?
A plugin architecture, by definition, is to let third parties add code
to your application. This rather precludes being able to simply link it in.
But why go through the trouble of doing dynamic linking? You still can
have a plugin architecture without dynamic linking.
When it's a commercial program, the DLL plugin approach probably
wouldn't work anyway: in order to enable others to compile plugins, you
would need to expose your internal "headers" (D modules). Note that
unlike in languages like C/C++, this would cause internal modules to be
exposed too, even if they are not strictly needed. What would you do to
avoid this? Maintain a separate set of import modules?
As Alexander Pánek said; you can just use .di files, which the compiler
can create from existing .d modules.
See my reply to his posting.
Heck, you can just use regular .d modules and stub out the
implementations. There's no reason why you'd need to release your code
to third parties.
Sure, if you like tedious work. And you have to be extremely careful.
Writing an extern(C) based interface will be not much more work, but the
result will be much more robust, and give you some extra advantages,
like enabling other languages to link to it.
Templates are a different matter, but then C++ has the same problem.
Whether or not you want to release your templates as part of the SDK
really depends on what they are. Templates + interfaces make a good pair.
Sure. Bytecode based languages like C# still can export compiled
generics, though. Of course, they are not as flexible as D or C++ templates.
I think a purely extern(C) based interface would be better in these cases.
In fact, if you rely on the D ABI for dynamic linking, you'll probably
have the same trouble as with C++ dynamic linking. For example, BeOS had
to go through this to make sure their C++ based API maintains ABI
compatibility:
http://homepage.corbina.net/~maloff/holy-wars/fbc.html
I'm not sure if the D ABI improves the situation. At any rate, it
doesn't sound like a good idea.
There's some interesting problems at that article that maybe we should
ask Walter about. For one, being able to control virtual function
ordering is an interesting idea.
But by and large, these are the same problems you'll get with ANY ABI.
If the size of a struct changes in a C ABI, you're hosed just as bad as
if the size of a struct in D, or the fields of a class.
I'm not sure, but I think you could solve many of these problems by
using linker symbols instead of compile time constants for sizes and
field offsets. Still doesn't work in D, because CTFE still needs them as
real compile time constants. And it'd probably be less efficient.
-- Daniel
