4) Thread local / global memory
A callback into the runtime needs to happen in the following cases:
- a __gshared variable is assigned
- a reference / pointer is casted to immutable
- a reference / pointer is casted to shared
void _d_castToGlobalMem(void* ptr);
This can be used by the GC to keep thread local pools of memory and move
a memory block to a global memory pool as soon as it is needed there.
If we'd want per-thread mark/sweeping then shared memory must never own
unshared memory. I think this could be done using a separate allocator for
shared/immutable data. For casts this would require a transitive move of
the
data or it'd need to be prohibited.
