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Fix computeIfAbsent resetting expireAfterWrite for existing entries - #8828
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agammann
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Nov 5, 2026
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Re-adding e at the tail of writeQueue while retaining its old write time breaks the queue's timestamp order. expireEntries() only removes expired entries from the head, so an older entry can sit behind a newer, unexpired one. For example, with concurrencyLevel(1) and expireAfterWrite(10 minutes): put A at t=0, B at t=5, then computeIfAbsent(A, ...) at t=6. At t=11, cleanUp() sees B at the head and leaves expired A counted in size(). Could this preserve A's write-queue position, and add a two-entry FakeTicker test for cleanup order?
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Fixes #3700
Calling
cache.asMap().computeIfAbsent()for a key that is already presentreset the entry's write timestamp, so with
expireAfterWritethe entryeffectively never expired as long as
computeIfAbsentkept being called.That contradicts the
Mapcontract forcomputeIfAbsent, which leaves anexisting mapping untouched, and it made an
expireAfterWritecache behavelike an
expireAfterAccessone for those keys.The cause is in
Segment.compute: when the remapping function returns thevery same value that is already stored, the code restored the old value
reference but still recorded a write, which updates the write timestamp.
This change records a read instead, which refreshes the access time but
leaves the write time alone, and re-adds the entry to the write queue so
it can still expire. The same branch covers
compute,computeIfPresentand
mergereturning the unchanged value, which get the same treatment.Repro, before the fix (a manual
Ticker,expireAfterWriteof 10minutes):
putat t=0,computeIfAbsenton the existing key at t=9,then
getIfPresentat t=11 returned the value. After the fix it returnsnull. A second check confirms
computeIfAbsentstill refreshes theaccess time for
expireAfterAccesscaches.Tests: added
testComputeIfAbsentDoesNotRefreshWriteTimeandtestComputeIfAbsentStillRefreshesAccessTimetoLocalCacheMapComputeTest.Ran
LocalCacheMapComputeTest,CacheExpirationTest,LocalCacheTestand
CacheEvictionTest: 10,370 tests, all passing.