Fix two eviction bugs in segcache#18
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compare_fifo sorted by newest-first (LIFO) due to a spurious .reverse() on the timestamp comparison. sort_by is ascending and index 0 is evicted first, so the correct sort is ascending by age — oldest segment first. can_evict() blocked eviction of any segment whose remaining TTL was less than 20 s (the former SEG_MATURE_TIME constant). For items stored with Duration::ZERO or any TTL under 20 s the cache would refuse to evict, returning NoFreeSegments on every insert once full. The fix is to remove the maturity condition entirely: a segment is evictable when it is Active and has a next-segment pointer (i.e. is not the current write target). Adds integration_eviction.rs with two new tests, one per bug. The FIFO test sleeps 1.1 s between fills to produce distinguishable timestamps at clocksource::coarse 1-second resolution. Co-Authored-By: Claude Sonnet 4.6 <[email protected]>
Co-Authored-By: Claude Sonnet 4.6 <[email protected]>
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Summary
compare_fifowas LIFO, not FIFO (eviction/mod.rs): the comparator called.reverse()on the timestamp sort, causingsort_by(ascending) to place the newest segment at index 0 — the slot evicted first. Removing.reverse()restores oldest-first ordering.can_evict()permanently blocked short-TTL segments (segments/header.rs): the previous condition(create_at + ttl) >= (now + SEG_MATURE_TIME)is equivalent to remaining TTL ≥ 20 s. Any segment holding items with TTL < 20 s could never be explicitly evicted, causingNoFreeSegmentswhen such a cache was full. The fix removes the maturity condition entirely — a segment is evictable when it isActiveand has anext_seg(i.e. is not the current write target).Test plan
cargo test -p segcache— 57 tests pass (40 unit, 2 integration_basic, 2 integration_eviction, 13 doc-tests)integration_eviction::random_evicts_short_ttl_segment_when_full— fills a 2-segment cache with 10 s-TTL items, asserts the next insert evicts successfullyintegration_eviction::fifo_evicts_oldest_segment_first— fills two generations of segments (1.1 s sleep for clocksource::coarse 1-second resolution), asserts the older generation is evicted and the newer survivescargo clippy --all-targets --all-features -- -D warnings— clean🤖 Generated with Claude Code