[GitHub] [arrow] jorgecarleitao edited a comment on pull request #8018: ARROW-9815 [Rust] [DataFusion] Fixed deadlock caused by accessing the scalar functions' registry.

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jorgecarleitao edited a comment on pull request #8018:
URL: https://github.com/apache/arrow/pull/8018#issuecomment-678609613


   Hey both, I think I implemented what we discussed, but the devil is always in the details.
   
   The main changes are:
   
   * `ExecutionContextState::datasources` and `ExecutionContextState::scalar_functions` are now boxed, not `Arc`. This is so that when we lock `ExecutionContextState`, both get locked, which means that we only need to lock `ExecutionContextState` (but threads can't change each independently).
   * `ExecutionContextState` is no longer clonable.
   * optimizers now expect references, not `Arc<Mutex<_>>`.
   * `SqlToRel` is now lifetimed, as it is now bound to `ExecutionContextState`.
   
   I feel that we should probably have a test to demonstrate that the `ExecutionContext` is thread safe (e.g. run two queries from two different threads).


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