Custom method instrumentation when running .java file "directly"

[breedx-splk]

I figured this was way too oddball/niche to bring up as an issue, but in doing some testing work today I discovered (the hard way) that the OTEL_INSTRUMENTATION_METHODS_INCLUDE setting that leverages the io.opentelemetry.methods tracer does not seem to be compatible with running .java files directly.

So in my case, something like this:

OTEL_INSTRUMENTATION_METHODS_INCLUDE="MyCoolClass[myCoolMethod]" \
java -javaagent:opentelemetry-javaagent.jar MyCoolClass.java

was failing to actually instrument the method. But if I did an explicit javac and instead run the resulting .class things work ok.

Anyway, I assume that there is a lifecycle or race condition with the classloaders, and that a screwball path happens when running java Whatever.java directly.

I would not expect many users to be impacted by this, but wanted this to be here for posterity. If folks think this is interesting or have insight, feel free to share.

[trask]

running java Whatever.java directly

what is this magic? 🛸

[breedx-splk]

I know, right!? It was supposed to be a shortcut....it was instead a find-the-problem side quest.

Anyway, I guess that came along in Java 11? I suspect nobody uses it outside of demos/talks. 🙃

[laurit]

Actually this seems to work on jdk17 and fail on jdk11. This is because there is a class resource presence check in

opentelemetry-java-instrumentation/instrumentation/methods/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/methods/MethodInstrumentation.java

Lines 38 to 40 in 8f32133

	public ElementMatcher<ClassLoader> classLoaderOptimization() {
	return hasClassesNamed(className);
	}

but the class loader used to load this class does not implement resource finders in jdk11 https://github.com/openjdk/jdk11u-dev/blob/d7a6e6ae495a780c6818dd69ae240ac092e41504/src/jdk.compiler/share/classes/com/sun/tools/javac/launcher/Main.java#L533 but does in jdk17 https://github.com/openjdk/jdk/blob/46bcc4901ea66589ec4c6904f8bab9156422312a/src/jdk.compiler/share/classes/com/sun/tools/javac/launcher/Main.java#L571

[breedx-splk]

Oh interesting for sure. I didn't try jdk17 in this case.

[trask]

wow, nice find