Would it make sense to add to Default exporters JVM's Safepoint metrics?

[mr-git]

Would it make sense to add to Default exporters JVM's Safepoint metrics?

HotspotRuntimeMBean exposes:

• getSafepointCount()
• getSafepointSyncTime()
• getTotalSafepointTIme()

In applications with many threads and long computations, these metrics can manifest how much time is spent before GC to get all threads to Safepoint and pause it.

[brian-brazil]

This sounds reasonable to add, though we'd need to check that they work on the various JVM implementations.

[darkl0rd]

Any idea when this functionality is going to be added? In the interim, is there a way to manually add these to the JMX exporter?

[dhoard]

I have some test code that calls sun.management.HotspotRuntimeMBean via reflection and support is not great.

For Java 6 OpenJDK-based VMs...

• fails

For Java 8 OpenJDK-based VMs...

• works

For Java 11 OpenJDK-based VMs...

• works with a warning

WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by io.prometheus.jmx.collector.HotSpotCollector (file:/temp/jmx_prometheus_javaagent.jar) to method sun.management.ManagementFactoryHelper.getHotspotRuntimeMBean()
WARNING: Please consider reporting this to the maintainers of io.prometheus.jmx.collector.HotSpotCollector
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

For Java 17 OpenJDK-based VMs...

• fails

java.lang.IllegalAccessException: class io.prometheus.jmx.collector.HotSpotCollector cannot access class sun.management.ManagementFactoryHelper (in module java.management) because module java.management does not export sun.management to unnamed module @7cf10a6f
	at java.base/jdk.internal.reflect.Reflection.newIllegalAccessException(Reflection.java:392)
	at java.base/java.lang.reflect.AccessibleObject.checkAccess(AccessibleObject.java:674)
	at java.base/java.lang.reflect.Method.invoke(Method.java:560)
	at io.prometheus.jmx.collector.HotSpotCollector.accessHotspotRuntimeMBean(HotSpotCollector.java:68)
	at io.prometheus.jmx.collector.HotSpotCollector.<init>(HotSpotCollector.java:48)
	at io.prometheus.jmx.exporter.Exporter.registerDefaultExports(Exporter.java:266)
	at io.prometheus.jmx.exporter.Exporter.start(Exporter.java:132)
	at io.prometheus.jmx.JavaAgent.premain(JavaAgent.java:50)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at java.instrument/sun.instrument.InstrumentationImpl.loadClassAndStartAgent(InstrumentationImpl.java:491)
	at java.instrument/sun.instrument.InstrumentationImpl.loadClassAndCallPremain(InstrumentationImpl.java:503)

For non OpenJDK-based VMs (IBM)

• fails