2fe0981fad
Now modifier stack wouldn't modify original curve's nurbs and will operate on a copy of nurbs. This makes it possible to process curve object update with shared curve datablocks from multiple threads. There's no big overhead for creating a copy of nurbs comparing to old behavior which was allocating original vertex array and apply coordinates on curve after all modifier are applied. The only remained issue with curves is curve's bounding box and texture space. It's not thread-safe, but it wouldn't lead to crashes -- it just could lead to either memory leak or wrong texture coordinates due to difference in modifiers stacks of objects which shares the same curve.