Intercept on Thread

[waihangcheung]

Hi,

I've been trying to intercept on Thread on application startup, and got no luck. I know that there are similar samples provided in the project but is there any specific config i should set? Or am i missing anything?

-javaagent:${BTRACE_HOME}/btrace-agent.jar=script=Test.class,noServer=true,scriptOutputFile=stdout.log

My btrace script

@BTrace
public class Test
{
    @OnMethod(clazz = "java.lang.Thread", method = "start")
    public static void onNewThread()
    {
        println("New thread spawned");
    }
}

My sample application

public class Main
{
    public static void main(String[] args) throws InterruptedException
    {
        Thread thread = new Thread()
        {
            public void run()
            {
                System.out.println("Thread Running");
            }
        };

        thread.start();
        thread.join();
        System.out.println("Thread done");
    }
}

[jbachorik]

BTrace needs to exclude any classes it requires to run the core functionality from the instrumentation candidates to prevent possible circularity errors during the invokedynamic bootstrap :(

Currently, the filter is a bit overzealous because I didn't have the time to fine-tune the excludes and as such all java.lang.* classes will not be instrumented.

Can you intercept a Runnable instead?

[waihangcheung]

I guess it's the same restriction for java.util.concurrent.*?

[waihangcheung]

No luck, Runnable is under java.lang.Runnable

[jbachorik]

It's also an interface :)
You would need something like clazz = "+java.lang.Runnable" to instrument all implementations.
That might be actually quite a lot of classes.

[waihangcheung]

clazz = "+java.lang.Runnable" does work.

I want to narrow it down to Kind.CALL, doesn't seem to work

    @OnMethod(clazz = "TargetClass", method = "targetMethod",
              location = @Location(value = Kind.CALL, clazz = "+java.lang.Runnable", method = "run"))

[jbachorik]

You could try patching

btrace/btrace-instr/src/main/java/org/openjdk/btrace/instr/ClassFilter.java

Line 189 in 46cf07f

return SENSITIVE_CLASSES.contains(name);

to exclude java.lang.Thread and test whether the agent starts normally and the method is properly traced.

I am away from my computer for next 5 days so there is no chance I might try this on my own.

[waihangcheung]

commented out java/lang/ & java/util/ , it seems to work fine. Thanks

Need to also enable startupRetransform=true

[jbachorik]

Modifications to the sensitive classes list will take more effort.
The problem is with invoke dynamic that is necessary for BTrace runnning on JDK 15 and newer - the linking of a dynamic call involves quite a lot of JDK classes and if any of them happen to be instrumented as well the whole JVM deadlocks.