What's the current status of dynamic loading (and/or linking) for D libraries?

I've been playing with this a bit in hopes of calling a D shared library from R through the C ABI, and noticed that on Windows it seems fine, but on Linux dmd won't build my library unless it includes main(), and it segfaults if I call writeln().

I've seen this thread:
http://forum.dlang.org/thread/hmhaldyfziejrplgzazt@forum.dlang.org

And also this one:
http://forum.dlang.org/thread/k3vfm9$1tq$1@digitalmars.com

What I gather is that right now, DLLs work on Windows, but on *nix, shared libraries cannot yet use anything from Phobos.

Am I correct that it's safe to dynamically load a D library on Windows? How out-of-date is the information in the tutorial for making DLLs on dlang?

Is supporting dynamically loadable libraries a priority for the developers, or something that might not happen for a while?

> Is supporting dynamically loadable libraries a priority for the developers, or something that might not happen for a while?

Judging by this thread:

http://forum.dlang.org/thread/kf1223$oo8$1@digitalmars.com

It has just become a priority.

On Sunday, 10 February 2013 at 22:11:52 UTC, Nick Ulle wrote:
> What's the current status of dynamic loading (and/or linking) for D libraries?
>
> I've been playing with this a bit in hopes of calling a D shared library from R through the C ABI, and noticed that on Windows it seems fine, but on Linux dmd won't build my library unless it includes main(), and it segfaults if I call writeln().
>
> I've seen this thread:
> http://forum.dlang.org/thread/hmhaldyfziejrplgzazt@forum.dlang.org
>
> And also this one:
> http://forum.dlang.org/thread/k3vfm9$1tq$1@digitalmars.com
>
> What I gather is that right now, DLLs work on Windows, but on *nix, shared libraries cannot yet use anything from Phobos.
> 
> Am I correct that it's safe to dynamically load a D library on Windows? How out-of-date is the information in the tutorial for making DLLs on dlang?
>
> Is supporting dynamically loadable libraries a priority for the developers, or something that might not happen for a while

For shared libraries (linux) I'd use ldc . It's just works.

On Sunday, 10 February 2013 at 23:41:54 UTC, John Colvin wrote:
> For shared libraries (linux) I'd use ldc . It's just works.

Not quite. Using
  ldc2 -shared -relocation-model=pic mylib.d
Compiles and links, but on loading there are undefined symbols (_Dmain). Including a main() function gets me a loadable library, but much like the case with dmd, it segfaults if I call writeln.

On Sunday, 10 February 2013 at 22:46:29 UTC, jerro wrote:
>
> Judging by this thread:
>
> http://forum.dlang.org/thread/kf1223$oo8$1@digitalmars.com
>
> It has just become a priority.

Thanks! This is great to hear. I didn't come across that thread while searching the forums before.

On Sunday, 10 February 2013 at 23:41:54 UTC, John Colvin wrote:
> For shared libraries (linux) I'd use ldc . It's just works.

You are living a dangerous life. ;)

It appears to work at first, but the test suite is known to segfault in random places with druntime/Phobos being built as a shared library, most probably because the GC/threading code doesn't really handle dynamic libraries at all.

David

You can arrange to have d's runtime initialized when dlopen loads
the shared lib by adding a small shim that uses gcc attributes,
as follows:

// shim.c

__attribute__((constructor))
static void dinit() {
     rt_init();
}
__attribute__((destructor))
static void dfini() {
     rt_term();
}

// end of shim.c

Compile this to a .o with gcc, then include the .o in the build.
Note that I've only tried this trick with a simple "hello world"
shared lib, so I apologize in advance if it doesn't work for
real-world uses.

On Sunday, 10 February 2013 at 22:11:52 UTC, Nick Ulle wrote:
> What's the current status of dynamic loading (and/or linking) for D libraries?
>
> I've been playing with this a bit in hopes of calling a D shared library from R through the C ABI, and noticed that on Windows it seems fine, but on Linux dmd won't build my library unless it includes main(), and it segfaults if I call writeln().

Dynamic linking works in linux (at least observed features work, see example http://forum.dlang.org/thread/k3vfm9$1tq$1@digitalmars.com?page=2). Dynamic loading does not work.

> Is supporting dynamically loadable libraries a priority for the developers, or something that might not happen for a while?

Yes, couple of days ago Walter announced that shared libraries is priority and he will get into this after releasing new dmd version.

On 02/10/2013 11:11 PM, Nick Ulle wrote:
> What's the current status of dynamic loading (and/or linking) for D
> libraries?
>
No dynamic loading in sight yet. We need to extend the GC, find semantics/techniques for TLS initialization, provide tools to load symbols ...
What is on the way but will take some more weeks is link-time support for shared libraries.
https://github.com/D-Programming-Language/druntime/pull/395

> I've been playing with this a bit in hopes of calling a D shared library
> from R through the C ABI, and noticed that on Windows it seems fine, but
> on Linux dmd won't build my library unless it includes main(), and it
> segfaults if I call writeln().
>
The reasons for your crashes are missing initialization.
You could experiment with calling rt_init/rt_term which are exported from your shared library, but only if you're not threaded.

> What I gather is that right now, DLLs work on Windows, but on *nix,
> shared libraries cannot yet use anything from Phobos.
>
Yes, there is rudimentary support on Windows, but you'll inevitably run into ODR issues.
http://d.puremagic.com/issues/show_bug.cgi?id=7020#c4

> Am I correct that it's safe to dynamically load a D library on Windows?
> How out-of-date is the information in the tutorial for making DLLs on
> dlang?
>
AFAIK it should work.

> Is supporting dynamically loadable libraries a priority for the
> developers, or something that might not happen for a while?

It's a huge priority but also a huge undertaking.

On Sunday, 10 February 2013 at 23:52:30 UTC, David Nadlinger wrote:
> On Sunday, 10 February 2013 at 23:41:54 UTC, John Colvin wrote:
>> For shared libraries (linux) I'd use ldc . It's just works.
>
> You are living a dangerous life. ;)
>
> It appears to work at first, but the test suite is known to segfault in random places with druntime/Phobos being built as a shared library, most probably because the GC/threading code doesn't really handle dynamic libraries at all.
>
> David

Does this pretty much completely invalidate projects like this: https://bitbucket.org/ariovistus/pyd ?

I've had success using it, as well as loading d shared libraries from C/IDL, with the appropriate rt_init calls etc.