Fix NPE

[roberttoyonaga]

Summary

Fixes a NPE encountered when attempting to connect with a non-hotspot VM.

Problem Description

See error stack trace here.

NPE occurs because FlightRecorderServiceV2.connection is not initialized before use. This can happen in the FlightRecorderServiceV2 constructor when isDynamicFlightRecorderSupported(IConnectionHandle) returns false because it calls ConnectionToolkit.isHotSpot(IConnectionHandle) which returns false for native images. This allows isFlightRecorderDisabled(IConnectionHandle) to be evaluated which results in the stack trace linked above.

Solution

Initialize FlightRecorderServiceV2.connection earlier.

[andrewazores]

That's occurring in the forked JMC code that we're carrying for downstream build purposes, so this means that at some point JMC itself was impacted by the same bug too. Could you verify if the same NPE occurs when you try to connect to your NI JMX server using JMC?

If JMC is affected then the best flow would be to work with them to fix it upstream, and then we pull that commit back down here, possibly as part of #95. If JMC is not affected (ie this bug is already fixed upstream) then we can accept this minor patch for now, but it would be superseded by the upstream fix when #95 is finished.

[roberttoyonaga]

That's occurring in the forked JMC code that we're carrying for downstream build purposes, so this means that at some point JMC itself was impacted by the same bug too. Could you verify if the same NPE occurs when you try to connect to your NI JMX server using JMC?

If JMC is affected then the best flow would be to work with them to fix it upstream, and then we pull that commit back down here, possibly as part of #95. If JMC is not affected (ie this bug is already fixed upstream) then we can accept this minor patch for now, but it would be superseded by the upstream fix when #95 is finished.

Ok I see. Yup I'll give it a try with JMC too!

[roberttoyonaga]

It seems as though I can connect to the NI mbean server and invoke operations on the FlightRecorderMXBean with JMC 8.01. So maybe the problem has been fixed upstream already.

[roberttoyonaga]

Yup, it looks like the problem has been fixed: https://github.com/openjdk/jmc/blob/master/application/org.openjdk.jmc.rjmx.services.jfr/src/main/java/org/openjdk/jmc/rjmx/services/jfr/internal/FlightRecorderServiceV2.java#L114

[andrewazores]

#155