jvm/heapAlloc/bytes not emitted when running Druid with JDK11+

[FrankChen021]

#12232 officially support JDK11.

But by staring Druid with JDK11 with the example configuration, we can see an exception message as

2022-03-06T14:29:48,890 WARN [main] org.apache.druid.java.util.metrics.AllocationMetricCollectors - Cannot initialize org.apache.druid.java.util.metrics.AllocationMetricCollector
java.lang.reflect.InaccessibleObjectException: Unable to make public long[] com.sun.management.internal.HotSpotThreadImpl.getThreadAllocatedBytes(long[]) accessible: module jdk.management does not "exports com.sun.management.internal" to unnamed module @6d0b5baf
        at java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:340) ~[?:?]
        at java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:280) ~[?:?]
        at java.lang.reflect.Method.checkCanSetAccessible(Method.java:198) ~[?:?]
        at java.lang.reflect.Method.setAccessible(Method.java:192) ~[?:?]
        at org.apache.druid.java.util.metrics.AllocationMetricCollectors.<clinit>(AllocationMetricCollectors.java:41) [druid-core-0.23.0-SNAPSHOT.jar:0.23.0-SNAPSHOT]
        at org.apache.druid.java.util.metrics.JvmMonitor.<init>(JvmMonitor.java:79) [druid-core-0.23.0-SNAPSHOT.jar:0.23.0-SNAPSHOT]
        at org.apache.druid.java.util.metrics.JvmMonitor.<init>(JvmMonitor.java:70) [druid-core-0.23.0-SNAPSHOT.jar:0.23.0-SNAPSHOT]
        at org.apache.druid.java.util.metrics.JvmMonitor.<init>(JvmMonitor.java:65) [druid-core-0.23.0-SNAPSHOT.jar:0.23.0-SNAPSHOT]

Since AllocationMetricCollector is not correctly initialized, the metric jvm/heapAlloc/bytes is not emitted.

Solution

To fix this problem, we have to add following option to the JVM parameter

--add-exports jdk.management/com.sun.management.internal=ALL-UNNAMED

I think it's better for us to detect the JDK version and automatically add above option to the JVM parameter in the shell(node.sh/run-druid) if current JDK is JDK11+