private void endThread() {
   if (softRefReleaseThread != null) {
     softRefReleaseThread.requestEnd = true;
     softRefReleaseThread.interrupt();
     softRefReleaseThread = null;
   }
 }
  private void startThread() {
    if (softRefReleaseThread != null) {
      throw new IllegalStateException(
          Messages.getString("vfs.impl/SoftRefReleaseThread-already-running.warn"));
    }

    softRefReleaseThread = new SoftRefReleaseThread();
    softRefReleaseThread.start();
  }