obs-ffmpeg: Use event for source reconnect thread

Fixes an issue where update/destroy of a media source during reconnect
would block the parent thread until the next reconnect attempt. This
would result in significant quantities of dropped frames, delayed OBS
shutdown, or frozen UI during this period.

plugins/obs-ffmpeg/obs-ffmpeg-source.c

@@ -55,8 +55,9 @@ struct ffmpeg_source {
 	bool is_stinger;
 
 	pthread_t reconnect_thread;
-	bool stop_reconnect;
+	pthread_mutex_t reconnect_mutex;
 	bool reconnect_thread_valid;
+	os_event_t *reconnect_stop_event;
 	volatile bool reconnecting;
 	int reconnect_delay_sec;
 
@@ -65,6 +66,23 @@ struct ffmpeg_source {
 	obs_hotkey_id stop_hotkey;
 };
 
+// Used to safely cancel and join any active reconnect threads
+// Use this to join any finished reconnect thread too!
+static void stop_reconnect_thread(struct ffmpeg_source *s)
+{
+	if (s->is_local_file)
+		return;
+	pthread_mutex_lock(&s->reconnect_mutex);
+	if (s->reconnect_thread_valid) {
+		os_event_signal(s->reconnect_stop_event);
+		pthread_join(s->reconnect_thread, NULL);
+		s->reconnect_thread_valid = false;
+		os_atomic_set_bool(&s->reconnecting, false);
+		os_event_reset(s->reconnect_stop_event);
+	}
+	pthread_mutex_unlock(&s->reconnect_mutex);
+}
+
 static void set_media_state(void *data, enum obs_media_state state)
 {
 	struct ffmpeg_source *s = data;
@@ -347,10 +365,11 @@ static void ffmpeg_source_start(struct ffmpeg_source *s)
 static void *ffmpeg_source_reconnect(void *data)
 {
 	struct ffmpeg_source *s = data;
-	os_sleep_ms(s->reconnect_delay_sec * 1000);
 
-	if (s->stop_reconnect || s->media)
-		goto finish;
+	int ret = os_event_timedwait(s->reconnect_stop_event,
+				     s->reconnect_delay_sec * 1000);
+	if (ret == 0 || s->media)
+		return NULL;
 
 	bool active = obs_source_active(s->source);
 	if (!s->close_when_inactive || active)
@@ -359,8 +378,6 @@ static void *ffmpeg_source_reconnect(void *data)
 	if (!s->restart_on_activate || active)
 		ffmpeg_source_start(s);
 
-finish:
-	s->reconnect_thread_valid = false;
 	return NULL;
 }
 
@@ -378,17 +395,25 @@ static void ffmpeg_source_tick(void *data, float seconds)
 		s->destroy_media = false;
 
 		if (!s->is_local_file) {
-			if (!os_atomic_set_bool(&s->reconnecting, true)) {
+			pthread_mutex_lock(&s->reconnect_mutex);
+			if (!os_atomic_set_bool(&s->reconnecting, true))
 				FF_BLOG(LOG_WARNING, "Disconnected. "
 						     "Reconnecting...");
+			if (s->reconnect_thread_valid) {
+				os_event_signal(s->reconnect_stop_event);
+				pthread_join(s->reconnect_thread, NULL);
+				s->reconnect_thread_valid = false;
+				os_event_reset(s->reconnect_stop_event);
 			}
 			if (pthread_create(&s->reconnect_thread, NULL,
 					   ffmpeg_source_reconnect, s) != 0) {
 				FF_BLOG(LOG_WARNING, "Could not create "
 						     "reconnect thread");
+				pthread_mutex_unlock(&s->reconnect_mutex);
 				return;
 			}
 			s->reconnect_thread_valid = true;
+			pthread_mutex_unlock(&s->reconnect_mutex);
 		}
 	}
 }
@@ -434,14 +459,10 @@ static void ffmpeg_source_update(void *data, obs_data_t *settings)
 						 ? 10
 						 : s->reconnect_delay_sec;
 		s->is_looping = false;
-
-		if (s->reconnect_thread_valid) {
-			s->stop_reconnect = true;
-			pthread_join(s->reconnect_thread, NULL);
-			s->stop_reconnect = false;
-		}
 	}
 
+	stop_reconnect_thread(s);
+
 	ffmpeg_options = obs_data_get_string(settings, "ffmpeg_options");
 
 	s->close_when_inactive =
@@ -594,6 +615,20 @@ static void *ffmpeg_source_create(obs_data_t *settings, obs_source_t *source)
 	struct ffmpeg_source *s = bzalloc(sizeof(struct ffmpeg_source));
 	s->source = source;
 
+	// Manual type since the event can be signalled without an active thread
+	if (os_event_init(&s->reconnect_stop_event, OS_EVENT_TYPE_MANUAL)) {
+		FF_BLOG(LOG_ERROR, "Failed to initialize reconnect stop event");
+		bfree(s);
+		return NULL;
+	}
+
+	if (pthread_mutex_init(&s->reconnect_mutex, NULL)) {
+		FF_BLOG(LOG_ERROR, "Failed to initialize reconnect mutex");
+		os_event_destroy(s->reconnect_stop_event);
+		bfree(s);
+		return NULL;
+	}
+
 	s->hotkey = obs_hotkey_register_source(source, "MediaSource.Restart",
 					       obs_module_text("RestartMedia"),
 					       restart_hotkey, s);
@@ -625,16 +660,15 @@ static void ffmpeg_source_destroy(void *data)
 {
 	struct ffmpeg_source *s = data;
 
+	stop_reconnect_thread(s);
+
 	if (s->hotkey)
 		obs_hotkey_unregister(s->hotkey);
-	if (!s->is_local_file) {
-		s->stop_reconnect = true;
-		if (s->reconnect_thread_valid)
-			pthread_join(s->reconnect_thread, NULL);
-	}
 	if (s->media)
 		media_playback_destroy(s->media);
 
+	pthread_mutex_destroy(&s->reconnect_mutex);
+	os_event_destroy(s->reconnect_stop_event);
 	bfree(s->input);
 	bfree(s->input_format);
 	bfree(s->ffmpeg_options);