uloop: add support for interval timers

So far, the only way to implement periodic interval timers was to use
one-shot uloop_timeout timers which are rearmed within their completion
callback immediately on expiration.

While simple, this approach is not very precise and interval lengths will
slowly drift over time, due to callback execution overhead, scheduling
granularity etc.

In order to make uloop provide stable and precise interval timer
capabilities, this commit introduces a new `uloop_interval` structure
along with the new related `uloop_interval_set()`, `uloop_interval_cancel()`
and `uloop_interval_remaining()` api functions.

Periodic timers are implemented using the timerfd facility an Linux and
kqueue EVFILT_TIMER events on macOS/BSD.

The Lua binding has been updated to include support for the new timer type
as well.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

1 files changed, 59 insertions, 0 deletions

diff --git a/uloop-kqueue.c b/uloop-kqueue.c
index c1275b0..a48cca0 100644
--- a/uloop-kqueue.c
+++ b/uloop-kqueue.c
@@ -103,6 +103,23 @@ static int __uloop_fd_delete(struct uloop_fd *fd)
 	return register_poll(fd, 0);
 }
 
+static int64_t get_timestamp_us(void)
+{
+#ifdef CLOCK_MONOTONIC
+	struct timespec ts = { 0, 0 };
+
+	clock_gettime(CLOCK_MONOTONIC, &ts);
+
+	return ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
+#else
+	struct timeval tv = { 0, 0 };
+
+	gettimeofday(&tv, NULL);
+
+	return tv.tv_sec * 1000000 + tv.tv_usec;
+#endif
+}
+
 static int uloop_fetch_events(int timeout)
 {
 	struct timespec ts;
@@ -115,6 +132,16 @@ static int uloop_fetch_events(int timeout)
 
 	nfds = kevent(poll_fd, NULL, 0, events, ARRAY_SIZE(events), timeout >= 0 ? &ts : NULL);
 	for (n = 0; n < nfds; n++) {
+		if (events[n].filter == EVFILT_TIMER) {
+			struct uloop_interval *tm = events[n].udata;
+
+			tm->private.time.fired = get_timestamp_us();
+			tm->expirations += events[n].data;
+			tm->cb(tm);
+
+			continue;
+		}
+
 		struct uloop_fd_event *cur = &cur_fds[n];
 		struct uloop_fd *u = events[n].udata;
 		unsigned int ev = 0;
@@ -148,3 +175,35 @@ static int uloop_fetch_events(int timeout)
 	}
 	return nfds;
 }
+
+static int timer_register(struct uloop_interval *tm, unsigned int msecs)
+{
+	struct kevent ev;
+
+	tm->private.time.msecs = msecs;
+	tm->private.time.fired = get_timestamp_us();
+
+	EV_SET(&ev, (uintptr_t)tm, EVFILT_TIMER, EV_ADD, NOTE_USECONDS, msecs * 1000, tm);
+
+	return kevent(poll_fd, &ev, 1, NULL, 0, NULL);
+}
+
+static int timer_remove(struct uloop_interval *tm)
+{
+	struct kevent ev;
+
+	EV_SET(&ev, (uintptr_t)tm, EVFILT_TIMER, EV_DELETE, 0, 0, NULL);
+
+	return kevent(poll_fd, &ev, 1, NULL, 0, NULL);
+}
+
+static int64_t timer_next(struct uloop_interval *tm)
+{
+	int64_t t1 = tm->private.time.fired;
+	int64_t t2 = get_timestamp_us();
+
+	while (t1 < t2)
+		t1 += tm->private.time.msecs * 1000;
+
+	return (t1 - t2) / 1000;
+}