Avoid the per-request rotation copy in round-robin address selection#2230
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hyperxpro merged 8 commits intoJul 18, 2026
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RoundRobinAddressSelector.rotateBy allocated a fresh ArrayList (backing array of size n) plus two subList views on every multi-IP round-robin request whose selected index != 0 — i.e. (n-1)/n of requests for an n-IP host — just to present the resolved addresses in round-robin failover order. Return a lightweight read-only view (RotatedView, one small wrapper over the resolved list + a start index) instead of copying: element i maps to resolved.get((index + i) mod size). All consumers only read the result (get/size/iteration — NettyChannelConnector's failover loop and deprioritizeCooling), and the resolved list is not mutated after being wrapped, so no copy is needed. index == 0 and single-IP hosts still return the resolved list unchanged (no allocation), as before. Only affects the opt-in LoadBalance.ROUND_ROBIN path. Existing selector tests (rotation order/evenness/failover completeness) pass unchanged; adds tests asserting the full element-by-element rotation order and that the returned view is read-only. No API change: rotateBy and RotatedView are private; rotate()'s signature is unchanged.
hyperxpro
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Jul 18, 2026
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@pavel-ptashyts please fix merge conflicts |
…e-alloc # Conflicts: # client/src/main/java/org/asynchttpclient/netty/channel/RoundRobinAddressSelector.java
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@hyperxpro done |
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…eck (#2257) Motivation: #2230 replaced the per-request rotation copy in `RoundRobinAddressSelector` with a lightweight read-only `RotatedView`. Two follow-ups remained: the new view no longer implemented `RandomAccess`, causing consumers that optimize for indexed access to fall back to iterator-based traversal, and its bounds-checking behavior was not covered by tests. Modification: Make `RotatedView` implement `RandomAccess` and add a `rotatedViewRejectsOutOfBoundsAccess` test to verify that `get(size)` and `get(-1)` throw `IndexOutOfBoundsException`. Result: `RotatedView` now preserves the `RandomAccess` contract of the `ArrayList` it replaced, allowing consumers to retain indexed fast paths, and its bounds-checking behavior is protected by regression tests.
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RoundRobinAddressSelector.rotateBy allocated a fresh ArrayList (backing array of size n) plus two subList views on every multi-IP round-robin request whose selected index != 0 — i.e. (n-1)/n of requests for an n-IP host — just to present the resolved addresses in round-robin failover order.
Return a lightweight read-only view (RotatedView, one small wrapper over the resolved list + a start index) instead of copying: element i maps to resolved.get((index + i) mod size). All consumers only read the result (get/size/iteration — NettyChannelConnector's failover loop and deprioritizeCooling), and the resolved list is not mutated after being wrapped, so no copy is needed. index == 0 and single-IP hosts still return the resolved list unchanged (no allocation), as before.
Only affects the opt-in LoadBalance.ROUND_ROBIN path. Existing selector tests (rotation order/evenness/failover completeness) pass unchanged; adds tests asserting the full element-by-element rotation order and that the returned view is read-only.
No API change: rotateBy and RotatedView are private; rotate()'s signature is unchanged.