@Override
  public void setNotifyBySubscription(boolean b) {
    checkRunning();
    if (CacheServerImpl.ENABLE_NOTIFY_BY_SUBSCRIPTION_FALSE) {
      notifyBySubscription = b;
    }
  }
Checks to see whether or not this cache server is running. If so, an
{@link IllegalStateException} is thrown.
geode-core/src/main/java/org/apache/geode/internal/cache/CacheServerImpl.java