HDFS-17813. NameCache promotes wrong object reference on threshold crossing#8313
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balodesecurity wants to merge 1 commit intoapache:trunkfrom
Open
HDFS-17813. NameCache promotes wrong object reference on threshold crossing#8313balodesecurity wants to merge 1 commit intoapache:trunkfrom
balodesecurity wants to merge 1 commit intoapache:trunkfrom
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…ossing. In NameCache.promote(), cache.put(name, name) stored the caller's argument as the cached value instead of useCount.value (the original object captured when the entry was first inserted into the transient map). This caused two distinct heap objects to exist for the same logical name, defeating the purpose of the cache (memory deduplication / object identity reuse). Fix: pass UseCount to promote() and store useCount.value as the cache value. Added testPromotionPreservesObjectIdentity to TestNameCache to assert that the object returned after promotion is the same reference (assertSame) as the one originally inserted.
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Problem
In
NameCache.put(), when a name's use count crosses the promotion threshold, the cache was populated with the caller'snameargument rather than the originaluseCount.valuethat was stored in the transient map:This means after promotion the cache holds a different object reference than what was stored before promotion. Any caller that held a reference to the pre-promotion value now has a stale reference, and two distinct
Stringobjects exist for what should be a single cached identity — wasting memory and breaking reference equality.Fix
Pass
useCountinto thepromote()helper and storeuseCount.valueinstead:This preserves the original object reference across the promotion boundary.
Testing
TestNameCache#testPromotionPreservesObjectIdentity: creates aNameCachewith threshold 2, inserts a non-internedString, triggers promotion, and usesassertSameto verify the returned reference is identical before and after promotion.