From e410ecc9957ddf27201fa67a9fe7705270d54c1a Mon Sep 17 00:00:00 2001
From: Norman Feske <norman.feske@genode-labs.com>
Date: Wed, 12 Aug 2015 09:58:58 +0200
Subject: [PATCH] timer test: trigger timeout-masking bug

Issue #1646
---
 repos/os/src/test/timer/main.cc | 47 ++++++++++++++++++++++++++++++---
 1 file changed, 43 insertions(+), 4 deletions(-)

diff --git a/repos/os/src/test/timer/main.cc b/repos/os/src/test/timer/main.cc
index 38ff43c92..899c78a56 100644
--- a/repos/os/src/test/timer/main.cc
+++ b/repos/os/src/test/timer/main.cc
@@ -75,6 +75,37 @@ class Timer_client : public Genode::List<Timer_client>::Element,
 };
 
 
+/**
+ * Timer client that continuously reprograms timeouts
+ */
+struct Timer_stressful_client : Timer::Connection, Genode::Thread<STACK_SIZE>
+{
+	unsigned long us;
+
+	/*
+	 * In principle, we could constantly execute 'trigger_once' in a busy loop.
+	 * This however would significantly skew the precision of the timer on
+	 * platforms w/o priority support. The behaviour would highly depend on the
+	 * kernel's scheduling and its parameters such as the time-slice length. To
+	 * even out those kernel-specific peculiarities, we let the stressful
+	 * client delay its execution after each iteration instead of keeping it
+	 * busy all the time. The delay must be smaller than scheduled 'us' to
+	 * trigger the edge case of constantly reprogramming timeouts that never
+	 * trigger.
+	 */
+	Timer::Connection delayer;
+
+	void entry() { for (;;) { trigger_once(us); delayer.usleep(us/2); } }
+
+	Timer_stressful_client(unsigned long us)
+	:
+		Thread("timer_stressful_client"), us(us)
+	{
+		Genode::Thread<STACK_SIZE>::start();
+	}
+};
+
+
 using namespace Genode;
 
 extern "C" int usleep(unsigned long usec);
@@ -87,10 +118,18 @@ int main(int argc, char **argv)
 	static Genode::List<Timer_client> timer_clients;
 	static Timer::Connection main_timer;
 
-	/* check long single timeout */
-	printf("register two-seconds timeout...\n");
-	main_timer.msleep(2000);
-	printf("timeout fired\n");
+	/*
+	 * Check long single timeout in the presence of another client that
+	 * reprograms timeouts all the time.
+	 */
+	{
+		/* will get destructed at the end of the current scope */
+		Timer_stressful_client stressful_client(250*1000);
+
+		printf("register two-seconds timeout...\n");
+		main_timer.msleep(2000);
+		printf("timeout fired\n");
+	}
 
 	/* check periodic timeouts */
 	Signal_receiver           sig_rcv;