We used to set shader->osl_surface_ref during shader compilation and then
pushed it into the shared vectors.
This worked as long as everything was serial - but after the multithreading
change, we a) compile everything and then b) build the shared vectors since
just pushing into them from multiple threads would not work.
However, if there are multiple devices, then each shader will be compiled
multiple times - so in the end, shader->osl_surface_ref etc. will be set
to the last device's value. Then, we end up pushing that value into every
device's vectors, which breaks for the earler devices.
The fix is simple - just preallocate the vectors and pass the correct index
into the compilation function. This way, each thread can safely store its
result and we can get rid of shader->osl_surface_ref entirely.
Note that while multiple shaders are compiled in parallel, the loop over
devices for a given shader is serial, so there's no concern of conflicts
over other shader internals.
Pull Request: https://projects.blender.org/blender/blender/pulls/146617
fc5c6ab374