Fix quadratic performance issue in AsyncQueue<Serial>
#1840
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Adding an item to `AsyncQueue` was linear in the number of pending queue items, thus adding n items to an `AsyncQueue` before any can execute is in O(n^2). This decision was made intentionally because the primary use case for `AsyncQueue` was to track pending LSP requests, of which we don’t expect to have too many pending requests at any given time. While we can't fix the quadratic performance issue in general, we can resolve the quadratic issue of `AsyncQueue<Serial>` by making a new task only depend on the last item in the queue, which then transitively depends on all the previous items. `AsyncQueue<Serial>` are the queues that are most likely to contain many items. Fixes swiftlang#1725 rdar://137886469
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@swift-ci Please test |
hamishknight
approved these changes
Nov 22, 2024
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| /// Whether the task described by `self` needs to finish executing before | ||
| /// `other` can start executing. | ||
| func isDependency(of other: Self) -> Bool |
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Could keep both requirements and add a default implementation of dependencies(in:) that does the filtering. Don't really mind though
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I think it’s good to make adopters a little more aware of the potentially quadratic issue.
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Adding an item to
AsyncQueuewas linear in the number of pending queue items, thus adding n items to anAsyncQueuebefore any can execute is in O(n^2). This decision was made intentionally because the primary use case forAsyncQueuewas to track pending LSP requests, of which we don’t expect to have too many pending requests at any given time.While we can't fix the quadratic performance issue in general, we can resolve the quadratic issue of
AsyncQueue<Serial>by making a new task only depend on the last item in the queue, which then transitively depends on all the previous items.AsyncQueue<Serial>are the queues that are most likely to contain many items.Fixes #1725
rdar://137886469