On Friday, 18 March 2016 at 18:52:25 UTC, Jacob Carlborg wrote:
On 17/03/16 21:27, bitwise wrote:
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.
How does it behave on Linux? It already supports dynamic
libraries.
After looking at the elf implementation, Johannes's explanation
seems to be correct. I don't think it's the best solution though.
I'm wondering if the _exact_ behavior of the current solution was
intentional. It seems like everything will work fine as long as
you only use statically linked shared libs, so I'm wondering if
dynamic linking was fully considered at the time the current
solution was written. As far as dynamic linking goes, I don't
like how the current solution works. It can lead to very
confusing problems, and I think it would be better to do an
all-or-nothing approach:
-statically linked shared libs always have shared static ctors
called
-statically linked shared libs always have TLS static ctors
called for all new threads
-dynamically linked shared libs always have shared static ctors
called
-dynamically linked shared libs NEVER have TLS static ctors
called for ANY thread
I can see how one could argue for benefits of the current
approach, but I don't think it's worth exposing people to that
kind of confusion, to have partially working TLS static ctors.
Thoughts?
Bit
