From 37b3431e0079f988e2b4b5121e429bb23c02a261 Mon Sep 17 00:00:00 2001
From: Andri Yngvason <andri@yngvason.is>
Date: Wed, 29 Jun 2022 12:31:25 +0000
Subject: [PATCH] main: Add a canary ticker

This should help to notice when something is badly blocking the main loop.
---
 include/time-util.h | 46 +++++++++++++++++++++++++++++++++++++++++++++
 src/main.c          | 36 +++++++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+)
 create mode 100644 include/time-util.h

diff --git a/include/time-util.h b/include/time-util.h
new file mode 100644
index 0000000..9f9fa2b
--- /dev/null
+++ b/include/time-util.h
@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2019 - 2020 Andri Yngvason
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
+ * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#pragma once
+
+#include <time.h>
+#include <stdint.h>
+
+static inline uint64_t timespec_to_us(const struct timespec* ts)
+{
+	return (uint64_t)ts->tv_sec * UINT64_C(1000000) +
+	       (uint64_t)ts->tv_nsec / UINT64_C(1000);
+}
+
+static inline uint64_t timespec_to_ms(const struct timespec* ts)
+{
+	return (uint64_t)ts->tv_sec * UINT64_C(1000) +
+	       (uint64_t)ts->tv_nsec / UINT64_C(1000000);
+}
+
+static inline uint64_t gettime_us(void)
+{
+	struct timespec ts = { 0 };
+	clock_gettime(CLOCK_MONOTONIC, &ts);
+	return timespec_to_us(&ts);
+}
+
+static inline uint64_t gettime_ms(void)
+{
+	struct timespec ts = { 0 };
+	clock_gettime(CLOCK_MONOTONIC, &ts);
+	return timespec_to_ms(&ts);
+}
diff --git a/src/main.c b/src/main.c
index 3a47b4e..a508f63 100644
--- a/src/main.c
+++ b/src/main.c
@@ -45,6 +45,10 @@
 #include "renderer.h"
 #include "renderer-egl.h"
 #include "linux-dmabuf-unstable-v1.h"
+#include "time-util.h"
+
+#define CANARY_TICK_PERIOD INT64_C(100000) // us
+#define CANARY_LETHALITY_LEVEL INT64_C(8000) // us
 
 struct window {
 	struct wl_surface* wl_surface;
@@ -70,6 +74,7 @@ static struct wl_list seats;
 struct pointer_collection* pointers;
 struct keyboard_collection* keyboards;
 static int drm_fd = -1;
+static uint64_t last_canary_tick;
 
 static bool have_egl = false;
 
@@ -670,6 +675,35 @@ failure:
 	return -1;
 }
 
+static void on_canary_tick(void* obj)
+{
+	(void)obj;
+
+	uint64_t t = gettime_us();
+	int64_t dt = t - last_canary_tick;
+	last_canary_tick = t;
+
+	int64_t delay = dt - CANARY_TICK_PERIOD;
+
+	// Early ticks are just a result of late ticks...
+	if (delay < CANARY_LETHALITY_LEVEL)
+		return;
+
+	fprintf(stderr, "WARNING: Long delays observed (%"PRIi64"). Something is blocking the main loop\n",
+				delay);
+}
+
+static void create_canary_ticker(void)
+{
+	last_canary_tick = gettime_us();
+
+	struct aml* aml = aml_get_default();
+	struct aml_ticker* ticker = aml_ticker_new(CANARY_TICK_PERIOD / 1000ULL,
+			on_canary_tick, NULL, NULL);
+	aml_start(aml, ticker);
+	aml_unref(ticker);
+}
+
 void run_main_loop_once(void)
 {
 	struct aml* aml = aml_get_default();
@@ -862,6 +896,8 @@ int main(int argc, char* argv[])
 
 	wl_display_dispatch(wl_display);
 
+	create_canary_ticker();
+
 	while (do_run)
 		run_main_loop_once();