The JShell regression test support class AbstractStopExecutionTest.java provides code that starts a JShell evaluation in one thread and then invokes JShell.stop() to interrupt that evaluation from another thread.

This class uses a boolean field to synchronize the action between threads. However, this field is not marked volatile and so the communication is unreliable. As a result, in rare cases, the test can fail due to a timeout.

The simple fix is to make the field volatile. This has been verified in testing.