From: Ben Harris <bjh21@bjh21.me.uk>
Date: Sun, 18 Nov 2018 10:47:36 +0000 (+0000)
Subject: Create a timer to catch CLOCK_REALTIME going backwards.
X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~bjharris/git?a=commitdiff_plain;h=48352981d095de1592069147d4f2c9f546d313aa;p=clunk.git

Create a timer to catch CLOCK_REALTIME going backwards.

Not used yet: I've spotted a couple of other problems to fix first.
---

diff --git a/clunk.c b/clunk.c
index 70c767e..5a54f61 100644
--- a/clunk.c
+++ b/clunk.c
@@ -32,6 +32,13 @@ static int statefd = -1;
 
 static sigset_t signals_to_block;
 
+/*
+ * The fallback timer protects us from occasions when CLOCK_REALTIME
+ * goes backwards so our nice absolute clock_nanosleep() end up
+ * sleeping far too long.
+ */
+static timer_t fallback_timer;
+
 static void
 dummy_out(bool state)
 {
@@ -118,12 +125,17 @@ static void
 init(int argc, char **argv)
 {
 	struct timespec ts;
+	struct sigevent sev;
 	int opt;
 
 	tzset();
 	sigemptyset(&signals_to_block);
 	sigaddset(&signals_to_block, SIGINT);
 	sigaddset(&signals_to_block, SIGTERM);
+	sev.sigev_notify = SIGEV_SIGNAL;
+	sev.sigev_signo = SIGALRM;
+	if (timer_create(CLOCK_MONOTONIC, &sev, &fallback_timer) != 0)
+		err(1, "timer_create");
 	if (clock_gettime(CLOCK_REALTIME, &ts) != 0)
 		err (1, "clock_gettime");
 	if (localtime_r(&ts.tv_sec, &displayed) == NULL)