Some backends (e.g kqueue, epoll) need to be told about closing a file +descriptor (either by calling close explicitly or by any other means, +such as dup). The reason is that you register interest in some file +descriptor, but when it goes away, the operating system will silently drop +this interest. If another file descriptor with the same number then is +registered with libev, there is no efficient way to see that this is, in +fact, a different file descriptor.

To avoid having to explicitly tell libev about such cases, libev follows +the following policy: Each time ev_io_set is being called, libev +will assume that this is potentially a new file descriptor, otherwise +it is assumed that the file descriptor stays the same. That means that +you have to call ev_io_set (or ev_io_init) when you change the +descriptor even if the file descriptor number itself did not change.

This is how one would do it normally anyway, the important point is that +the libev application should not optimise around libev but should leave +optimisations to libev.

+ + + +

ev_io_init (ev_io *, callback, int fd, int events)
ev_io_set (ev_io *, int fd, int events)

The special problem of disappearing file descriptors