Fix WeakConcurrentMap memory leak

[ozoz03]

We noticed that opentelemetry javaagent produces a memory leak and root class for this is io.opentelemetry.javaagent.tooling.muzzle.AgentCachingPoolStrategy as you can see from heap dump analysis:

From what can see in the code AgentCachingPoolStrategy uses WeakLockFreeCache

opentelemetry-java-instrumentation/muzzle/src/main/java/io/opentelemetry/javaagent/tooling/muzzle/AgentCachingPoolStrategy.java

Line 52 in f6bcd76

final Cache<ClassLoader, WeakReference<ClassLoader>> loaderRefCache = Cache.weak();

and it only calls the method computeIfAbsent() on it

opentelemetry-java-instrumentation/muzzle/src/main/java/io/opentelemetry/javaagent/tooling/muzzle/AgentCachingPoolStrategy.java

Line 71 in f6bcd76

loaderRefCache.computeIfAbsent(classLoader, WeakReference::new);

computeIfAbsent() makes calls to only two methods of the underlying WeekConcurrentMap.WithInlinedExpunction delegate object: getIfPresent() and putIfAbsent()

• opentelemetry-java-instrumentation/instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/cache/WeakLockFreeCache.java

  Line 21 in f6bcd76

  V value = get(key);

• opentelemetry-java-instrumentation/instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/cache/WeakLockFreeCache.java

  Line 46 in f6bcd76

  return delegate.getIfPresent(key);

• opentelemetry-java-instrumentation/instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/cache/WeakLockFreeCache.java

  Line 36 in f6bcd76

  V previous = delegate.putIfAbsent(key, value);

But WeekConcurrentMap.WithInlinedExpunction doesn't override those two methods and, thus, the expungeStaleEntries() method is not called and the weak keys are not removed from the map.

We think the described issue is the root cause of the observed memory leak and this pull request should fix it.

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Related to #5265

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Oleg Zasymenko (ebf787d)

[trask]

thanks!

[vinaya-devopsnow]

thanks