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Cannot initialize Polygot Sampler in --module-path mode #657

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Cannot initialize Polygot Sampler in --module-path mode#657
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thurka

Description

@JaroslavTulach
JaroslavTulach
opened on Mar 14, 2026
  • There is a problem initializing VisualVM 2.2 Polyglot Sampler with Truffle 25.0.0 when the application is running in module path mode.
  • this is caused by GR-54300 changes that modified the ENGINES field from Map to Set which remained unnoticed for a while

Reproduce

  • I've created a sample project https://github.com/jtulach/graaljs/tree/GraalJsDemo
  • when executed in module path mode: mvn -Pmodulepath package exec:exec the VisualVM Polyglot Sampler can't connect
    • everything works in classpath mode
    • everything also works when one --add-opens access for the access to findActiveEngines method...

Fix

CCing @thurka, @tzezula

Activity

  1. Imagethurka
    self-assigned this
    on Mar 15, 2026

  2. thurka commented on Mar 20, 2026

    @thurka
    thurka
    on Mar 20, 2026
    Member

    Thanks for the test-case. I am able to reproduce the issue.

    java.lang.reflect.InvocationTargetException
	at java.base/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:67)
	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:483)
	at org.graalvm.visualvm.sampler.truffle.stagent.TruffleJMX.getTruffleInstance(TruffleJMX.java:158)
	at org.graalvm.visualvm.sampler.truffle.stagent.TruffleJMX.agentmain(TruffleJMX.java:71)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
	at java.base/java.lang.reflect.Method.invoke(Method.java:565)
	at java.instrument@25.0.2/sun.instrument.InstrumentationImpl.loadClassAndStartAgent(InstrumentationImpl.java:544)
	at java.instrument@25.0.2/sun.instrument.InstrumentationImpl.loadClassAndCallAgentmain(InstrumentationImpl.java:566)
Caused by: java.lang.ClassCastException: class java.util.Collections$SynchronizedSet cannot be cast to class java.util.Map (java.util.Collections$SynchronizedSet and java.util.Map are in module java.base of loader 'bootstrap')
	at org.graalvm.visualvm.sampler.truffle.stagent.Truffle.getEnginesFromField(Truffle.java:199)
	at org.graalvm.visualvm.sampler.truffle.stagent.Truffle.getEnginesFromClass(Truffle.java:187)
	at org.graalvm.visualvm.sampler.truffle.stagent.Truffle.getEngines(Truffle.java:171)
	at org.graalvm.visualvm.sampler.truffle.stagent.Truffle.<init>(Truffle.java:68)
	at java.base/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:62)
  3. Imagethurka
    added a commit that references this issue on Mar 28, 2026

    GH-657 adapt to a new version of GraalVM - 'ENGINES' field can also c…

    cd18f81
  4. Imagethurka
    added the
    Bug
    issue type on Apr 3, 2026

  5. thurka commented on Apr 3, 2026

    @thurka
    thurka
    on Apr 3, 2026
    Member

    FIxed in master.

  6. Imagethurka
    closed this as completedon Apr 3, 2026
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