Use kqueue to respond to more than one event type

[Eric Radman]

This is a repost from a question I posed on stackoverflow, please ignore
if this is considered off-topic for this list.
--

When an event is registered with `kqueue` an ID relating to that event
type is supplied; for example a file descriptor is used to identify a file to
watch

int kq;
struct kevent ke;

kq = kqueue();
fd = open(argv[1], O_RDONLY);
EV_SET(&ke, fd, EVFILT_VNODE, EV_ADD, NOTE_DELETE | NOTE_RENAME, 0, NULL);
kevent(kq, &ke, 1, NULL, 0, NULL);

while (1) {
kevent(kq, NULL, 0, &ke, 1, NULL);
/* respond to file system event */
}

Now if I also need to respond to other event types such signals we need a new
instance of kqueue so as to avoid a conflict with the `ident` argument of
`kevent()`.

kq_sig = kqueue();
struct kevent ke_sig;

/* set the handler and ignore SIGINT */
signal(SIGINT, SIG_IGN);
EV_SET(&ke_sig, SIGINT, EVFILT_SIGNAL, EV_ADD, 0, 0, NULL);
kevent(kq_sig, &ke_sig, 1, NULL, 0, NULL);
while (1) {
kevent(kq_sig, NULL, 0, &ke_sig, 1, NULL);
/* respond signals */
}

Watching more than one event type appears to necessitate multiple
threads that act on shared state (receiving a signal could close a file
descriptor for example).

Is there a more general mechanism for sending a message from one thread
to another using kqueue? In some cases I can conceive of enabling and
disabling a filter as a means of edge-triggering another kevent.

--
Eric Radman | http://eradman.com

[Mark Heily]

On Wed, Apr 10, 2013 at 4:03 PM, Eric Radman <eric...@eradman.com> wrote:

This is a repost from a question I posed on stackoverflow, please ignore
if this is considered off-topic for this list.
--

snip

 

Is there a more general mechanism for sending a message from one thread
to another using kqueue? In some cases I can conceive of enabling and
disabling a filter as a means of edge-triggering another kevent.

I think the EVFILT_USER filter would allow you to signal other threads that are blocked in a kevent() call. This is an Apple extension to kqueue() that is not present on NetBSD and OpenBSD, however.