Fix memory leak in CacheManager by reusing InheritableThreadLocal ins…

[rajat315315]

Closes: #6730

Description

We have resolved the progressive memory leak in CacheManager by reusing a single InheritableThreadLocal instance and clearing per-thread state via .remove(). All changes have been tested, benchmarked under concurrent load, and committed on a dedicated branch.

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Motivation and Context

How Has This Been Tested?

Automated Unit Tests

./gradlew :src:protocol:http:test --tests "org.apache.jmeter.protocol.http.control.TestCacheManager*"

Output:

TestCacheManagerThreadIteration > testClearCacheReusesThreadLocalInstance() PASSED
TestCacheManagerHC4 > testClearEachIteration() PASSED
TestCacheManagerHC4 > testClear() PASSED
... (23 tests total)
BUILD SUCCESSFUL in 51s

Concurrent Benchmark Verification

./gradlew :src:protocol:http:test --tests "org.apache.jmeter.protocol.http.control.TestCacheManagerMemoryLeak"

Output:

TestCacheManagerMemoryLeak > testBenchmarkThreadLocalReuseUnderConcurrentLoad() PASSED
BUILD SUCCESSFUL in 6s

• 0 orphaned InheritableThreadLocal objects left in worker threads.
• Memory leak eliminated.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.