+/**
+ *
+ * add file descriptors to fd_sets
+ *
+ * The pre_select function of the activated selector gets called just before
+ * para_server enters its main select loop. The selector may add its own file
+ * descriptors to the \a rfds or the \a wfds set.
+ *
+ * \return The highest-numbered file descriptor which was added to either of
+ * the two fd sets (or -1 if no file descriptors were added).
+ *
+ * \sa select(2)
+ */
+int (*pre_select)(fd_set *rfds, fd_set *wfds);
+/**
+ * handle the file descriptors which are ready for I/O
+ *
+ * If the pre_select hook added one ore more file descriptors to the read or write
+ * set, this is the hook to check the result and do any I/O on those descriptors
+ * which are ready for reading/writing.
+ */
+void (*post_select)(fd_set *rfds, fd_set *wfds);
+/**
+ * each selector has its private data pointer */
+void *private_data;