private void checkRunning() {
    if (isRunning()) {
      throw new IllegalStateException(
          "A cache server's configuration cannot be changed once it is running.");
    }
  }
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