+/*
+ * general notes about epoll:
+ *
+ * a) epoll silently removes fds from the fd set. as nothing tells us
+ * that an fd has been removed otherwise, we have to continually
+ * "rearm" fds that we suspect *might* have changed (same
+ * problem with kqueue, but much less costly there).
+ * b) the fact that ADD != MOD creates a lot of extra syscalls due to a)
+ * and seems not to have any advantage.
+ * c) the inability to handle fork or file descriptors (think dup)
+ * limits the applicability over poll, so this is not a generic
+ * poll replacement.
+ *
+ * lots of "weird code" and complication handling in this file is due
+ * to these design problems with epoll, as we try very hard to avoid
+ * epoll_ctl syscalls for common usage patterns.
+ */