On Thu, 21 May 2015 15:34:56 -0400, Jacob Carlborg <d...@me.com> wrote:
On 2015-05-21 10:12, Timothee Cour via Digitalmars-d wrote:
dlopen() of a D shared library works when called from a C++ file, and
that a C++ file can call multiple D shared libraries simultaneously when
using RTLD_LAZY option.
Before waiting for a full solution with an integrated druntime, is there
at least a way to have a separate runtime in each shared library, so
that dlopen() can be called from a D file?
No, not out of the box.
I'm not sure if I remember all the details correctly, but this is
basically how it works:
The runtime uses the "_dyld_register_func_for_add_image" function
provided by the dynamic linker. This function is used to register a
callback. The callback will be called for each currently loaded image
(executable/dynamic library) in the executable. The callback will also
be called for every newly loaded image, i.e. using dlopen. You need to
keep track of which image is yourself and which are other images you
should ignore.
Then, the other problem with "_dyld_register_func_for_add_image" is that
it's not possible to unregister the callback. Which means, if you
register a callback using this function from a dynamic library loaded
with dlopen and then unload it. Next time dlopen is called it will
crash, because the callback points to an address that doesn't exist
anymore.
There's an other, undocumented, function that does basically the same
but prevents the issue with the callback by not allowing the dynamic
library to be unloaded.
So does that mean that "_dyld_register_func_for_add_image" shouldn't be
called at all from shared libs at all then? The fact that there is no
"unregister" function seems to suggest that it's meant to be called once
from the main executable to add a callbacck that survives the entire life
of the program. Can't whatever the callback does be done from the runtime
linked to the main executable?
Bit
