anderslanglands / bbl-usd-rs Goto Github PK

I've started to use the crate in a multithreaded way and it's proving to be a little bit of a pain. According to https://openusd.org/dev/api/_usd__page__multi_threading.html, the USD threading model is essentially the same as Rusts: multiple readers or a single writer. It should be valid to unsafe impl both Send and Sync for everything.

Currently, essentially all methods take &self, e.g.

pub fn prim_at_path<P: Into<sdf::Path>>(&self, path: P) -> Result<Prim, Error>;

This is problematic when modifying a prims attributes comes into consideration, as currently this will allow writing to the stage from two seperate threads which (usually) results in a segfault.

you could have two seperate methods for read/write vs read-only prims:

pub fn prim_at_path_<P: Into<sdf::Path>>(&self, path: P) -> Result<Prim, Error>;
pub fn prim_mut_at_path<P: Into<sdf::Path>>(&mut self, path: P) -> Result<PrimMut, Error>;

But this doesn't properly reflect the fact that both prim types are effectively borrowing the stage they exist within, meaning that you could keep a PrimMut around after the write-access to the stage has ended. Adding lifetime annotations is probably a no-go as well.

A better solution is to wrap the whole stage in an Arc'd RwLock of some kind, and clone that when accessing any prim or attribute, locking it for either read or write depending on what's being read out. Implementing this would be a massive pain though and you'd probably want two implementations for both blocking and async locks.