A DESCRIPTION OF THE PROBLEM :
Once the ContextClassLoader is changed on a thread in ForkJoinPool.commonPool() to a custom ClassLoader, it cannot be manually reset to the original value (ClassLoader.getSystemClassLoader()).

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile and start the supplied java program.
The program executes a task by using the ForkJoinPool.commonPool() which first changes the ContextClassLoader to a custom ClassLoader and then changes it back to the original ClassLoader.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The ContextClassCloader can be reset to its original value.
ACTUAL -
The ContextClassLoader remains the custom ClassLoader.

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public class ContextClassLoaderInForkJoinPoolCommonPool {
    public static void main(String[] args) throws InterruptedException, ExecutionException {

        CountDownLatch latch = new CountDownLatch(1);

        ForkJoinPool.commonPool().execute(() -> {
            Thread thread = Thread.currentThread();

            ClassLoader originalCCL = thread.getContextClassLoader();

            // Set a custom ContextClassLoader and verify that it has been set
            ClassLoader customCCL = new URLClassLoader(new URL[0]);
            thread.setContextClassLoader(customCCL);
            if (thread.getContextClassLoader() != customCCL) {
                throw new RuntimeException("ERROR: cannot set custom ContextClassLoader");
            }

            // Restore the original ContextClassLoader and verify that it has been set
            thread.setContextClassLoader(originalCCL);
            if (thread.getContextClassLoader() != originalCCL) {
                throw new RuntimeException("ERROR: cannot reset to original ContextClassLoader");
            }

            latch.countDown();
        });

        latch.await();
    }
}
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