/** fds that should be watched for readability. */
fd_set rfds;
/** fds that should be watched for writability. */
fd_set wfds;
/** Highest numbered file descriptor in any of the above fd sets. */
int max_fileno;
/** fds that should be watched for readability. */
fd_set rfds;
/** fds that should be watched for writability. */
fd_set wfds;
/** Highest numbered file descriptor in any of the above fd sets. */
int max_fileno;