public synchronized void close() {
    resetPoolManager();
    is_closed = true;

    C3P0Registry.markClosed(this);

    if (Debug.DEBUG && Debug.TRACE == Debug.TRACE_MAX && logger.isLoggable(MLevel.FINEST)) {
      logger.log(
          MLevel.FINEST,
          this.getClass().getName()
              + '@'
              + Integer.toHexString(System.identityHashCode(this))
              + " has been closed. ",
          new Exception("DEBUG STACK TRACE for PoolBackedDataSource.close()."));
    }
  }