Move wakeup into the main thread to remove complexity. Looks like CLOCK_MONOTONIC_COARSE doesn't need a syscall.

adsbus/wakeup.c

@@ -9,29 +9,19 @@
 #include <time.h>
 #include <string.h>
 #include <sys/epoll.h>
-#include <pthread.h>
 
 #include "common.h"
 
 #include "wakeup.h"
 
-struct wakeup_peer {
-	struct peer peer;
-	struct peer *inner_peer;
-};
-
-struct wakeup_request {
+struct wakeup_entry {
 	int fd;
 	uint64_t absolute_time_ms;
-};
-
-struct wakeup_entry {
-	struct wakeup_request request;
+	struct peer *peer;
 	struct wakeup_entry *next;
 };
 
-static pthread_t wakeup_thread;
-static int wakeup_write_fd;
+struct wakeup_entry *head = NULL;
 
 static uint64_t wakeup_get_time_ms() {
 	struct timespec tp;
@@ -41,13 +31,44 @@ static uint64_t wakeup_get_time_ms() {
 	return (tp.tv_sec * MS_PER_S) + (tp.tv_nsec / NS_PER_MS);
 }
 
-static void wakeup_request_add(struct wakeup_entry **head, struct wakeup_request *request) {
-	struct wakeup_entry *entry = malloc(sizeof(*entry));
-	memcpy(&entry->request, request, sizeof(entry->request));
+void wakeup_init() {
+}
 
-	struct wakeup_entry *prev = NULL, *iter = *head;
+void wakeup_cleanup() {
+	while (head) {
+		struct wakeup_entry *next = head->next;
+		free(head);
+		head = next;
+	}
+}
+
+int wakeup_get_delay() {
+	if (!head) {
+		return -1;
+	}
+	int delay = head->absolute_time_ms - wakeup_get_time_ms();
+	return delay < 0 ? 0 : delay;
+}
+
+void wakeup_dispatch() {
+	uint64_t now = wakeup_get_time_ms();
+	while (head && head->absolute_time_ms <= now) {
+		struct peer *peer = head->peer;
+		struct wakeup_entry *next = head->next;
+		free(head);
+		head = next;
+		peer->event_handler(peer);
+	}
+}
+
+void wakeup_add(struct peer *peer, uint32_t delay_ms) {
+	struct wakeup_entry *entry = malloc(sizeof(*entry));
+	entry->absolute_time_ms = wakeup_get_time_ms() + delay_ms;
+	entry->peer = peer;
+
+	struct wakeup_entry *prev = NULL, *iter = head;
 	while (iter) {
-		if (iter->request.absolute_time_ms > entry->request.absolute_time_ms) {
+		if (iter->absolute_time_ms > entry->absolute_time_ms) {
 			break;
 		}
 		prev = iter;
@@ -58,112 +79,7 @@ static void wakeup_request_add(struct wakeup_entry **head, struct wakeup_request
 		entry->next = prev->next;
 		prev->next = entry;
 	} else {
-		entry->next = *head;
-		*head = entry;
+		entry->next = head;
+		head = entry;
 	}
 }
-
-static void *wakeup_main(void *arg) {
-	int read_fd = (intptr_t) arg;
-
-	int epoll_fd = epoll_create1(0);
-	assert(epoll_fd >= 0);
-
-	struct epoll_event ev = {
-		.events = EPOLLIN,
-		.data = {
-			.fd = read_fd,
-		},
-	};
-	assert(!epoll_ctl(epoll_fd, EPOLL_CTL_ADD, read_fd, &ev));
-
-	struct wakeup_entry *head = NULL;
-
-	while (1) {
-		int delay = -1;
-		if (head) {
-			// This call is the whole reason we need a separate thread: we want to avoid getting the time inside the tight main thread loop.
-			delay = head->request.absolute_time_ms - wakeup_get_time_ms();
-			delay = delay < 0 ? 0 : delay;
-		}
-
-#define MAX_EVENTS 1
-		struct epoll_event events[MAX_EVENTS];
-		int nfds = epoll_wait(epoll_fd, events, MAX_EVENTS, delay);
-		if (nfds == -1 && errno == EINTR) {
-			continue;
-		}
-
-		if (nfds == 1) {
-			assert(events[0].data.fd == read_fd);
-			struct wakeup_request request;
-			ssize_t result = read(read_fd, &request, sizeof(request));
-			if (result == 0) {
-				// Peer closed connection, shutdown thread
-				break;
-			}
-			assert(result == sizeof(request));
-			wakeup_request_add(&head, &request);
-		} else {
-			assert(nfds == 0);
-		}
-
-		uint64_t now = wakeup_get_time_ms();
-		while (head && head->request.absolute_time_ms <= now) {
-			close(head->request.fd);
-			struct wakeup_entry *next = head->next;
-			free(head);
-			head = next;
-		}
-	}
-
-	while (head) {
-		close(head->request.fd);
-		struct wakeup_entry *next = head->next;
-		free(head);
-		head = next;
-	}
-
-	assert(!close(read_fd));
-	assert(!close(epoll_fd));
-	return NULL;
-}
-
-static void wakeup_handler(struct peer *peer) {
-	struct wakeup_peer *outer_peer = (struct wakeup_peer *) peer;
-	assert(!close(outer_peer->peer.fd));
-
-	struct peer *inner_peer = outer_peer->inner_peer;
-	free(outer_peer);
-	inner_peer->event_handler(inner_peer);
-}
-
-void wakeup_init() {
-	int pipefd[2];
-	assert(!pipe2(pipefd, O_NONBLOCK));
-	assert(!pthread_create(&wakeup_thread, NULL, wakeup_main, (void *) (intptr_t) pipefd[0]));
-	wakeup_write_fd = pipefd[1];
-}
-
-void wakeup_cleanup() {
-	assert(!close(wakeup_write_fd));
-	assert(!pthread_join(wakeup_thread, NULL));
-}
-
-void wakeup_add(struct peer *peer, uint32_t delay_ms) {
-	int pipefd[2];
-	assert(!pipe2(pipefd, O_NONBLOCK));
-
-	struct wakeup_request request = { 0 };
-	request.fd = pipefd[1],
-	request.absolute_time_ms = wakeup_get_time_ms() + delay_ms;
-	assert(write(wakeup_write_fd, &request, sizeof(request)) == sizeof(request));
-
-	struct wakeup_peer *outer_peer = malloc(sizeof(*outer_peer));
-	assert(outer_peer);
-	outer_peer->peer.fd = pipefd[0];
-	outer_peer->peer.event_handler = wakeup_handler;
-	outer_peer->inner_peer = peer;
-
-	peer_epoll_add((struct peer *) outer_peer, EPOLLRDHUP);
-}