fix: 25225 Fix race condition in EntityIdUniquenessValidator

[imalygin]

Problem

EntityIdUniquenessValidator#checkEntityUniqueness is invoked concurrently by multiple ProcessorTask threads. Every 100,000 entities, one thread calls StateUtils.resetStateCache() (to prevent OOM), which clears the readCache of every ReadableKVState while sibling threads are mid-get(). Since ReadableKVStateBase.get() writes to the cache and then re-reads it to produce its return value, a reset between those two steps causes get() to return null for an entity that actually exists. The result: counter ends up at 0 and the validator reports a spurious "No entity found for Entity ID X" failure.

This manifested as intermittent failures on different entity IDs across runs.

Fix

Guard state access with a ReentrantReadWriteLock:

• Reads (state.get(...)) acquire the read lock — concurrency preserved.
• resetStateCache() acquires the write lock — waits for in-flight reads to drain before clearing caches.

Fixes #25225

Notes for reviewer:

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

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[lfdt-bot]

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[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Coverage ∅ diff coverage · +0.00% coverage variation

Metric	Results
Coverage variation	✅ +0.00% coverage variation (-1.00%)
Diff coverage	✅ ∅ diff coverage

View coverage diff in Codacy

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (198285b)	100192	78875	78.72%
Head commit (0b92f7f)	100192 (+0)	78875 (+0)	78.72% (+0.00%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#25226)	0	0	∅ (not applicable)

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@            Coverage Diff            @@
##               main   #25226   +/-   ##
=========================================
  Coverage     74.90%   74.90%           
  Complexity    11524    11524           
=========================================
  Files          2586     2586           
  Lines        100289   100289           
  Branches      11087    11087           
=========================================
  Hits          75119    75119           
  Misses        21364    21364           
  Partials       3806     3806           

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[github-actions]

Flaky Test(s) Detected

One or more flaky tests were detected in this run. These tests have been reported before.

Test	Ticket
com.hedera.services.bdd.suites.freeze.JumpstartFileSuite#jumpstartsCorrectLiveWrappedRecordBlockHashes	#24927
com.hedera.services.bdd.suites.validation.LogValidationTest#logsContainNoUnexpectedProblems	#25154