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, 80 insertions, 0 deletions

diff --git a/uloop-epoll.c b/uloop-epoll.c
index 70e45e4..cf5733f 100644
--- a/uloop-epoll.c
+++ b/uloop-epoll.c
@@ -104,3 +104,83 @@ static int uloop_fetch_events(int timeout)
 
 	return nfds;
 }
+
+static void dispatch_timer(struct uloop_fd *u, unsigned int events)
+{
+	if (!(events & ULOOP_READ))
+		return;
+
+	uint64_t fired;
+
+	if (read(u->fd, &fired, sizeof(fired)) != sizeof(fired))
+		return;
+
+	struct uloop_interval *tm = container_of(u, struct uloop_interval, private.ufd);
+
+	tm->expirations += fired;
+	tm->cb(tm);
+}
+
+static int timer_register(struct uloop_interval *tm, unsigned int msecs)
+{
+	if (!tm->private.ufd.registered) {
+		int fd = timerfd_create(CLOCK_MONOTONIC, TFD_CLOEXEC|TFD_NONBLOCK);
+
+		if (fd == -1)
+			return -1;
+
+		tm->private.ufd.fd = fd;
+		tm->private.ufd.cb = dispatch_timer;
+	}
+
+	struct itimerspec spec = {
+		.it_value = {
+			.tv_sec = msecs / 1000,
+			.tv_nsec = (msecs % 1000) * 1000000
+		},
+		.it_interval = {
+			.tv_sec = msecs / 1000,
+			.tv_nsec = (msecs % 1000) * 1000000
+		}
+	};
+
+	if (timerfd_settime(tm->private.ufd.fd, 0, &spec, NULL) == -1)
+		goto err;
+
+	if (uloop_fd_add(&tm->private.ufd, ULOOP_READ) == -1)
+		goto err;
+
+	return 0;
+
+err:
+	uloop_fd_delete(&tm->private.ufd);
+	close(tm->private.ufd.fd);
+	memset(&tm->private.ufd, 0, sizeof(tm->private.ufd));
+
+	return -1;
+}
+
+static int timer_remove(struct uloop_interval *tm)
+{
+	int ret = __uloop_fd_delete(&tm->private.ufd);
+
+	if (ret == 0) {
+		close(tm->private.ufd.fd);
+		memset(&tm->private.ufd, 0, sizeof(tm->private.ufd));
+	}
+
+	return ret;
+}
+
+static int64_t timer_next(struct uloop_interval *tm)
+{
+	struct itimerspec spec;
+
+	if (!tm->private.ufd.registered)
+		return -1;
+
+	if (timerfd_gettime(tm->private.ufd.fd, &spec) == -1)
+		return -1;
+
+	return spec.it_value.tv_sec * 1000 + spec.it_value.tv_nsec / 1000000;
+}