CASSANDRA-21037 4.1 backport of CASSANDRA-19022 - nodetool gcstats on direct memory

[smiklosovic]

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[bschoening]

@smiklosovic I don't see a PR for 5.0, only 4.1 and 4.0

[Copilot]

Pull request overview

This PR backports CASSANDRA-19022 to the 4.1 branch, adding support for tracking direct memory in nodetool gcstats across different Java versions.

Key changes:

• Separates handling of Java 8's totalCapacity (long) and Java 11's TOTAL_CAPACITY (AtomicLong) fields
• Refactors the static initialization to attempt loading both field variants
• Introduces helper methods getField() and getFieldValue() for cleaner field access

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[Copilot]

The isAtomicLong parameter should be false for the Java 8 field. In Java 8, totalCapacity is a regular long field, not an AtomicLong. Only in Java 11 was it changed to TOTAL_CAPACITY as an AtomicLong.

This will cause a ClassCastException when running on Java 8, as the code will attempt to cast a Long to AtomicLong.

Suggested fix:

long fieldValue = getFieldValue(BITS_TOTAL_CAPACITY_JAVA_8, false);

Suggested change

	long fieldValue = getFieldValue(BITS_TOTAL_CAPACITY_JAVA_8, true);
	long fieldValue = getFieldValue(BITS_TOTAL_CAPACITY_JAVA_8, false);

[smiklosovic]

bad bot! This is not true, both of them are AtomicLong, it is just in Java 8 and 11 they differ on names.