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# Objective There's a repeating pattern of `ThreadLocal<Cell<Vec<T>>>` which is very useful for low overhead, low contention multithreaded queues that have cropped up in a few places in the engine. This pattern is surprisingly useful when building deferred mutation across multiple threads, as noted by it's use in `ParallelCommands`. However, `ThreadLocal<Cell<Vec<T>>>` is not only a mouthful, it's also hard to ensure the thread-local queue is replaced after it's been temporarily removed from the `Cell`. ## Solution Wrap the pattern into `bevy_utils::Parallel<T>` which codifies the entire pattern and ensures the user follows the contract. Instead of fetching indivdual cells, removing the value, mutating it, and replacing it, `Parallel::get` returns a `ParRef<'a, T>` which contains the temporarily removed value and a reference back to the cell, and will write the mutated value back to the cell upon being dropped. I would like to use this to simplify the remaining part of #4899 that has not been adopted/merged. --- ## Changelog TODO --------- Co-authored-by: Joseph <21144246+JoJoJet@users.noreply.github.com> |
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