Use an AtomicInt32 to count pendingUnitCount instead of using AsyncQueue
#1720
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…yncQueue` Adding an item to `AsyncQueue<Serial>` is 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. `SourceKitIndexDelegate` was also using `AsyncQueue` to track the number of pending units to be processed and eg. after indexing SourceKit-LSP, I have seen this grow up to ~20,000. With the quadratic behavior, this explodes time-wise. Turns out that we don’t actually need to use a queue here at all, an atomic is sufficient and much faster. Independently, we should consider mitigating the quadratic behavior of `AsyncQueue<Serial>` or `AsyncQueue` in general.
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hamishknight
approved these changes
Sep 27, 2024
This was referenced Oct 9, 2024
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Adding an item to
AsyncQueue<Serial>is 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.SourceKitIndexDelegatewas also usingAsyncQueueto track the number of pending units to be processed and eg. after indexing SourceKit-LSP, I have seen this grow up to ~20,000. With the quadratic behavior, this explodes time-wise.Turns out that we don’t actually need to use a queue here at all, an atomic is sufficient and much faster.
Independently, we should consider mitigating the quadratic behavior of
AsyncQueue<Serial>orAsyncQueuein general.