In ThreadsRunner.java, the following `run` method is responsible for coordinating all testing threads.

public void run() {
        ...
  try {
    start();,
    join();
    successful = dumpFailures() == 0;
                                      <--- the result is recorded and all memory for stressing can be released
  } catch ...
    ...
}

In the denoted line, we don't explicitly clean up test-running related data structures, making the test more vulnurable to OOM after the testing is effectively over.

    private List<Runnable> runnables = new ArrayList<Runnable>();
    private List<ManagedThread> threads = new ArrayList<ManagedThread>();

These two data structures are no longer needed after `successful = dumpFailures() == 0;`, so we can clear them.