code: synchronized void refreshAcls(Configuration conf) throws IOException {
      try {
        HashMap<String, AccessControlList> newAclsMap = 
          getQueueAcls(conf);
        aclsMap = newAclsMap;
      } catch (Throwable t) {
        String exceptionString = StringUtils.stringifyException(t);
        LOG.warn("Queue ACLs could not be refreshed because there was an " +
        		"exception in parsing the configuration: "+ exceptionString +
        		". Existing ACLs are retained.");
        throw new IOException(exceptionString);
      }
  
    }
docs: Refresh the acls for the configured queues in the system by reading
  it from mapred-queue-acls.xml.
  
  The previous acls are removed. Previously configured queues and
  if or not acl is disabled is retained.
  
  @throws IOException when queue ACL configuration file is invalid.