[Bug] ClassLoaderUtils.runAsClassLoader restores a stale context classloader captured at class-init time

[88fantasy]

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• I had searched in the issues and found no similar issues referencing ClassLoaderUtils / runAsClassLoader.

Java Version

Temurin 21.0.11 (console), built with Microsoft OpenJDK 11.0.28

Scala Version

2.12.x

StreamPark Version

3.0.0-SNAPSHOT (dev branch, commit 9ddda84c9)

Flink Version

1.20.4 and 2.2.1 (official binary distributions, standalone/remote cluster)

Deploy mode

remote

What happened

ClassLoaderUtils.runAsClassLoader(target, supplier) is meant to run a block under a given classloader and then put the calling thread back the way it found it. It does not: the finally restores ORIGINAL_CLASS_LOADER, a static final field initialised to Thread.currentThread().getContextClassLoader() at class-initialisation time — i.e. the context classloader of whichever thread first touched this class.

private static final ClassLoader ORIGINAL_CLASS_LOADER = Thread.currentThread().getContextClassLoader();

public static <R> R runAsClassLoader(ClassLoader targetClassLoader, Supplier<R> supplier) {
    try {
        Thread.currentThread().setContextClassLoader(targetClassLoader);
        return supplier.get();
    } finally {
        Thread.currentThread().setContextClassLoader(ORIGINAL_CLASS_LOADER);   // <-- not the caller's
    }
}

The method is called from shared thread-pool threads, so for any caller whose context classloader was not that same value on entry, the "restore" silently installs a different classloader on that thread and leaves it there. Nothing fails at the call site; the damage lands on whatever runs on that pooled thread next.

The correct behaviour is to capture the calling thread's own value on entry and restore that. ORIGINAL_CLASS_LOADER is still needed by cloneClassLoader() and stays.

This is not a regression from the recent Scala-to-Java migration — git log -p shows the Scala version had the same shape.

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