Blender Git Loki

Cycles: Fix race condition happening in progress utility

This is not enough to mutex-guard modification code of integer values,
since this operation is NOT atomic. This is not even safe for a single
byte data types.

For now guarded the getter functions, similar to other functions in
this module.

Ideally we want to switch modification to an atomic operations, so we
wouldn't need any locks in the getters.