[9.4] [ML] Fix concurrent LFU cache count invariant under lock timeouts (#3090)#3101
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) The concurrent cache only incremented m_NumberLookups inside the read-guard lambda, which does not run when the read lock times out. The subsequent miss path can still add a count (insert/increment) or record a lost update, so under contention the surviving counts could exceed the number of accounted lookups and intermittently trip checkInvariants() (observed as a flaky failure of testConcurrentReadsAndWrites on loaded debug CI agents). Count every lookup exactly once, before taking the read lock. Also relax the count invariant for the timeout-capable cache to a one-sided bound: counts can legitimately be lost under concurrency (an item hit under the read lock may be evicted before its count is incremented, one insert can evict several items, and write updates can time out) but must never be fabricated. The exact equality is retained for the single-threaded cache, which has no timeouts. Add a regression test that drives lock timeouts via a zero maximum wait under heavy contention; it fails reliably against the previous code. --------- Co-authored-by: Cursor <cursoragent@cursor.com> Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com> (cherry picked from commit 1beb813)
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