Merge pull request #593 from dawgfoto/dynamicLoading

[Benjamin Thaut]

Am 07.09.2013 19:09, schrieb Martin Nowak:
> We just merged the low-level implementation for full shared library
> support. There should be an article or some tutorial but I simply lack
> the time for that. So if you want to experiment with it you should read
> this and have a look at the test cases
> (https://github.com/D-Programming-Language/druntime/tree/master/test/shared).
>
> I'd be thankful for every bug report, please add the keyword dll
> (http://d.puremagic.com/issues/buglist.cgi?keywords=dll&resolution=---).
>
>
> Just a repost of the github comment
> (https://github.com/D-Programming-Language/druntime/pull/593#issuecomment-23913789).
>
>
> I updated and finished the low-level implementation.
> This now supports almost all shared library scenarios merely automatically.
> It is also tested pretty thoroughly.
> Here are the main gotchas for experimenting.
>
> There is an extra layer of thread local reference accounting over the
> global one in the runtime linker which has some implications on how to
> use shared libraries.
>
> Loading libraries should only be done through
> Runtime.loadLibrary/Runtime.unloadLibrary
> (or rt_loadLibrary/rt_unloadLibrary for C), so that the thread local
> accounting doesn't
> miss anything.
> The recommended pattern to load a D library from a pure C program is to
> dlopen
> phobos/druntime first and to use rt_loadLibrary/rt_unloadLibrary hereafter.
>
> Loading a library only initializes it and it's linked dependencies for
> the current
> thread.
>
> Threads where a library is not initialize will not see the library's
> modules, nor the EH
> tables and the GC will miss to scan the library's TLS memory.
>
> A spawned thread (core.thread.Thread) will initialize the same libraries
> as it's parent
> thread. There is an implicit dlopen call for every dynamically loaded
> library so to
> prevent the parent thread from unloading. When a thread finishes it will
> drop/unload all
> remaining references to loaded libraries.
> The high-level implementation of the shared libraries support will
> provide a method to
> iterate over all loaded libraries, thus it will be possible to
> explicitly unload unused
> inherited libraries.
>
> Finding the dependencies of a library is somewhat expensive so it is
> only performed for D libraries and non-recursively.
>
> Because all dependencies are loaded before the library itself we do know
> the recursive dependencies. In case of loading a C library that depends
> on D libraries or for D->C->D dependency chains we will miss the
> recursive dependency.
> This might possibly lead to uninitialized threads when loading such a
> library in more than one thread.
> I will try to fix any arising bugs ASAP but I don't have much time left
> currently.
> Please tag bugzilla entries with the dll keyword.
>
> Work on the high-level interface will start around the end of next week.

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