spurious NullPointerException in ArrayByteBufferPool.release()

[loetifuss]

Jetty version(s)
Jetty 12.0.15

Jetty Environment
core

Java version/vendor (use: java -version)
JDK 17.0.12

OS type/version
RedHat Linux

Description
After upgrading from Jetty 9 to 12 we're experiencing intermittent NullPointerExceptions, mostly from EventSourceSevlet.
Jetty is running embedded in an OSGI environment.

java.lang.NullPointerException: Cannot invoke "org.eclipse.jetty.io.RetainableByteBuffer.getByteBuffer()" because "buffer" is null
	at org.eclipse.jetty.io.ArrayByteBufferPool.release(ArrayByteBufferPool.java:281)
	at org.eclipse.jetty.io.ArrayByteBufferPool$Buffer.release(ArrayByteBufferPool.java:653)
	at org.eclipse.jetty.io.ArrayByteBufferPool.removeAndRelease(ArrayByteBufferPool.java:244)
	at org.eclipse.jetty.ee10.servlet.HttpOutput.lockedReleaseBuffer(HttpOutput.java:605)
	at org.eclipse.jetty.ee10.servlet.HttpOutput.onWriteComplete(HttpOutput.java:226)
	at org.eclipse.jetty.ee10.servlet.HttpOutput.flush(HttpOutput.java:690)
	at org.eclipse.jetty.ee10.servlet.ServletApiResponse.flushBuffer(ServletApiResponse.java:405)
	at org.eclipse.jetty.ee10.servlets.EventSourceServlet$EventSourceEmitter.flush(EventSourceServlet.java:223)
	at org.eclipse.jetty.ee10.servlets.EventSourceServlet$EventSourceEmitter.data(EventSourceServlet.java:169)

How to reproduce?

Not yet reproducible, seems to occur mostly during daytime under load:

[joakime]

Upgrade to Jetty 12.0.15 at least, and try again.
This is fixed already.

[loetifuss]

Upgrading to Jetty 12.0.15 didn't help. Still seeing these errors frequently.

[gregw]

@loetifuss Can you tell us anything else about the requests and responses? How are they read/generated? Are they big/small? Are they json/binary/??? Are you writing async or blocking? When it is not from the EventSourceServlet, where is it from?

[gregw]

@lorban My reading of the code is that the entry can only have a null buffer if it has not yet been enabled, or was enabled but the pool was terminated

@loetifuss Can you also tell us if you configure your buffer pool? If so then how?

[lorban]

@gregw your reading is right if the entry was a ConcurrentEntry instance, but I'm wondering if that instance wasn't a QueuedEntry?