@Override
  public void connectionClosed(ConnectionEvent event) {
    if (isActive) {
      try {
        PooledConnection conn = (PooledConnection) event.getSource();
        provider.returnConnection(conn);
      } catch (Exception ex) {
        String exception = "GemFireConnPooledDataSource::connectionclosed:Exception =" + ex;
        if (logger.isDebugEnabled()) {
          logger.debug(exception, ex);
        }
      }
    }
  }
Implementation of call back function from ConnectionEventListener interface. This callback will
be invoked on connection close event.
geode-core/src/main/java/org/apache/geode/internal/datasource/GemFireConnPooledDataSource.java