From f21eeefb37d05e1be993ef7adabf38a37a57240b Mon Sep 17 00:00:00 2001
From: Derek Foreman <derek.foreman@collabora.com>
Date: Mon, 22 Apr 2024 08:54:48 -0500
Subject: [PATCH] client: print a warning for undispatched queues when
 debugging

Forgetting to dispatch a queue can be very hard to debug, so let's try
to make that a little easier by printing a warning if any queue has
undispatched events for more than 3 seconds.

We can only check this when we're in libwayland for some reason, so let's
check when marshalling a request or when dispatching events on any queue.

Signed-off-by: Derek Foreman <derek.foreman@collabora.com>
---
 src/wayland-client.c | 52 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/src/wayland-client.c b/src/wayland-client.c
index cb5342e9..638807ff 100644
--- a/src/wayland-client.c
+++ b/src/wayland-client.c
@@ -78,6 +78,8 @@ struct wl_event_queue {
 	struct wl_list proxy_list; /**< struct wl_proxy::queue_link */
 	struct wl_display *display;
 	char *name;
+	uint64_t last_dispatch;
+	bool logged_stale_dispatch_warning;
 	struct wl_list link; /**< struct wl_display::queue_list */
 };
 
@@ -118,6 +120,36 @@ struct wl_display {
 
 static int debug_client = 0;
 
+static void
+wl_display_debug_dispatch(struct wl_display *display)
+{
+	struct wl_event_queue *queue;
+	struct timespec tp;
+	uint64_t now;
+
+	clock_gettime(CLOCK_MONOTONIC, &tp);
+	now = timespec_to_msec(&tp);
+
+	wl_list_for_each(queue, &display->queue_list, link) {
+		if (wl_list_empty(&queue->event_list) ||
+		    queue->logged_stale_dispatch_warning)
+			continue;
+
+		if (now > queue->last_dispatch + 3000) {
+			struct timespec tp;
+			unsigned int realtime;
+
+			clock_gettime(CLOCK_REALTIME, &tp);
+			realtime = (tp.tv_sec * 1000000L) + (tp.tv_nsec / 1000);
+			fprintf(stderr, "[%7u.%03u] {%s} has undispatched"
+                                        " events for more than 3 seconds\n",
+                                        realtime / 1000, realtime % 1000,
+                                        queue->name ? queue->name : "Unnamed queue");
+			queue->logged_stale_dispatch_warning = true;
+		}
+	}
+}
+
 /**
  * This helper function wakes up all threads that are
  * waiting for display->reader_cond (i. e. when reading is done,
@@ -233,6 +265,14 @@ wl_event_queue_init(struct wl_event_queue *queue,
 	if (name)
 		queue->name = strdup(name);
 
+	if (debug_client) {
+		struct timespec tp;
+
+		clock_gettime(CLOCK_MONOTONIC, &tp);
+		queue->last_dispatch = timespec_to_msec(&tp);
+		queue->logged_stale_dispatch_warning = false;
+	}
+
 	wl_list_insert(&display->queue_list, &queue->link);
 }
 
@@ -908,6 +948,9 @@ wl_proxy_marshal_array_flags(struct wl_proxy *proxy, uint32_t opcode,
 
 	pthread_mutex_lock(&disp->mutex);
 
+	if (debug_client)
+		wl_display_debug_dispatch(disp);
+
 	message = &proxy->object.interface->methods[opcode];
 	if (interface) {
 		new_proxy = create_outgoing_proxy(proxy, message,
@@ -2171,6 +2214,15 @@ wl_display_dispatch_queue_pending(struct wl_display *display,
 
 	ret = dispatch_queue(display, queue);
 
+	if (debug_client) {
+		struct timespec tp;
+
+		clock_gettime(CLOCK_MONOTONIC, &tp);
+		queue->last_dispatch = timespec_to_msec(&tp);
+		queue->logged_stale_dispatch_warning = false;
+		wl_display_debug_dispatch(display);
+	}
+
 	pthread_mutex_unlock(&display->mutex);
 
 	return ret;