Improve handling of LinkageErrors during LMAX Disruptor initializatio…

[ramanathan1504]

FIxes #2250

Reference URLs

• https://logging.apache.org/log4j/2.x/manual/async.html
• https://github.com/LMAX-Exchange/disruptor
• https://lists.apache.org/thread/ynxrn9vsmdqs31jrml71xb582o7m74qf

What was done

• Added defensive LinkageError handling in DisruptorUtil when creating async logger exception handlers.
• Added a shared error log helper to emit a clear classpath/version mismatch message for Disruptor linkage problems.
• Guarded sequenceCallback.set(sequence) with a null check in RingBufferLogEventHandler4 to prevent NPE when callback is not initialized.

[vy]

Simplify logging

[vy]

Added defensive LinkageError handling in DisruptorUtil when creating async logger exception handlers.

I don't see that.

Guarded sequenceCallback.set(sequence) with a null check in RingBufferLogEventHandler4 to prevent NPE when callback is not initialized.

I don't see that either.

[vy]

Suggested change

	final int version;
	try {
	Class.forName(
	"com.lmax.disruptor.SequenceReportingEventHandler", true, DisruptorUtil.class.getClassLoader());
	"com.lmax.disruptor.SequenceReportingEventHandler", false, DisruptorUtil.class.getClassLoader());
	version = 3;
	return 3;
	} catch (final ClassNotFoundException e) {
	return 4;
	} catch (final ClassNotFoundException ignored) {
	version = 4;
	}
	int version = 4;
	try {
	Class.forName(
	"com.lmax.disruptor.SequenceReportingEventHandler", false, DisruptorUtil.class.getClassLoader());
	version = 3;
	return 3;
	} catch (final ClassNotFoundException ignored) {
	// Do nothing
	}

[ramanathan1504]

Added defensive LinkageError handling in DisruptorUtil when creating async logger exception handlers.

I don't see that.

Guarded sequenceCallback.set(sequence) with a null check in RingBufferLogEventHandler4 to prevent NPE when callback is not initialized.

I don't see that either.

Forgot to mention this earlier @vy — for this PR, @ppkarwasz suggested that we do not need additional LinkageError handling here, since Log4j is already designed to handle it during the initialization stage. The main goal is just to provide better visibility to the user about what is happening.

That’s why I reverted the extra LinkageError handling from the earlier commit and only kept the logging message improvement.

dc9f81f