Move swaybar's event loop to common directory and refactor

* The loop functions are now prefixed with `loop_`.
* It is now easy to add timers to the loop.
* Timers are implemented using pollfd and timerfd, rather than manually
checking them when any other event happens to arrive.

common/loop.c

@@ -0,0 +1,105 @@
+#include <string.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <poll.h>
+#include <sys/timerfd.h>
+#include <unistd.h>
+#include "list.h"
+#include "log.h"
+#include "loop.h"
+
+struct loop_event {
+	void (*callback)(int fd, short mask, void *data);
+	void *data;
+};
+
+struct loop {
+	struct pollfd *fds;
+	int fd_length;
+	int fd_capacity;
+
+	list_t *events; // struct loop_event
+};
+
+struct loop *loop_create(void) {
+	struct loop *loop = calloc(1, sizeof(struct loop));
+	if (!loop) {
+		wlr_log(WLR_ERROR, "Unable to allocate memory for loop");
+		return NULL;
+	}
+	loop->fd_capacity = 10;
+	loop->fds = malloc(sizeof(struct pollfd) * loop->fd_capacity);
+	loop->events = create_list();
+	return loop;
+}
+
+void loop_destroy(struct loop *loop) {
+	list_foreach(loop->events, free);
+	list_free(loop->events);
+	free(loop);
+}
+
+void loop_poll(struct loop *loop) {
+	poll(loop->fds, loop->fd_length, -1);
+
+	for (int i = 0; i < loop->fd_length; ++i) {
+		struct pollfd pfd = loop->fds[i];
+		struct loop_event *event = loop->events->items[i];
+
+		// Always send these events
+		unsigned events = pfd.events | POLLHUP | POLLERR;
+
+		if (pfd.revents & events) {
+			event->callback(pfd.fd, pfd.revents, event->data);
+		}
+	}
+}
+
+struct loop_event *loop_add_fd(struct loop *loop, int fd, short mask,
+		void (*callback)(int fd, short mask, void *data), void *data) {
+	struct pollfd pfd = {fd, mask, 0};
+
+	if (loop->fd_length == loop->fd_capacity) {
+		loop->fd_capacity += 10;
+		loop->fds = realloc(loop->fds, sizeof(struct pollfd) * loop->fd_capacity);
+	}
+
+	loop->fds[loop->fd_length++] = pfd;
+
+	struct loop_event *event = calloc(1, sizeof(struct loop_event));
+	event->callback = callback;
+	event->data = data;
+
+	list_add(loop->events, event);
+
+	return event;
+}
+
+struct loop_event *loop_add_timer(struct loop *loop, int ms,
+		void (*callback)(int fd, short mask, void *data), void *data) {
+	int fd = timerfd_create(CLOCK_MONOTONIC, 0);
+	struct itimerspec its;
+	its.it_interval.tv_sec = 0;
+	its.it_interval.tv_nsec = 0;
+	its.it_value.tv_sec = ms / 1000000000;
+	its.it_value.tv_nsec = (ms * 1000000) % 1000000000;
+	timerfd_settime(fd, 0, &its, NULL);
+
+	return loop_add_fd(loop, fd, POLLIN, callback, data);
+}
+
+bool loop_remove_event(struct loop *loop, struct loop_event *event) {
+	for (int i = 0; i < loop->events->length; ++i) {
+		if (loop->events->items[i] == event) {
+			list_del(loop->events, i);
+
+			loop->fd_length--;
+			memmove(&loop->fds[i], &loop->fds[i + 1], sizeof(void*) * (loop->fd_length - i));
+
+			free(event);
+			return true;
+		}
+	}
+	return false;
+}

common/meson.build

@@ -5,6 +5,7 @@ lib_sway_common = static_library(
 		'cairo.c',
 		'ipc-client.c',
 		'log.c',
+		'loop.c',
 		'list.c',
 		'pango.c',
 		'readline.c',