static ctors in shared libs

[Johannes Pfau via Digitalmars-d]

Am Thu, 17 Mar 2016 20:27:39 +0000
schrieb bitwise <bitwise.pvt at gmail.com>:

> I've been doing some work on shared libraries for OSX, and have 
> come across a potential problem, which I'm not sure what to do 
> with.
> 
> Currently, when a thread is spawned, that thread calls all the 
> TLS ctors, then runs the thread entry point function, and finally 
> calls the TLS dtors before the thread terminates.
> 
> Example, for windows:
> 
> https://github.com/D-Programming-Language/druntime/blob/15a227477a344583c4748d95492703901417f4f8/src/core/thread.d#L236
> 
> So, the question is, how do dynamic libraries interact here?
> 
> Example: A dynamic library contains D modules with TLS ctors. If 
> I start a few threads, and then load a dynamic library, shouldn't 
> the TLS ctors in the dynamic library be called for each running 
> thread? If my assumption is correct, the next question is, how do 
> you do this?
> 
> I don't think you can hijack each thread and have it run the TLS 
> ctors, and you can run them all from the thread loading the 
> shared library because of synchronization issues. So what's the 
> solution? Should TLS ctors in dynamic libraries simply be 
> specified not to run, or could they somehow be run lazily at the 
> first TLS access in a dynamic library?
> 
> Any thoughts on this would be appreciated.
> 
> Thanks,
>     Bit
> 

It's been some time since I looked at that code, but IIRC TLS ctors for
newly loaded libraries are not run in old threads. There's nothing we
can do about this without help from the C runtime.


As TLS ctors are meant to initialize TLS storage the correct time to
run these is after the per-thread TLS storage allocation. (The C
runtime can actually allocate TLS memory lazily, on the first access to
a TLS variable in a module). The C runtimes of course know when TLS
storage is allocated, but they do not provide hooks we could use.