Making timeouts work with suspend

[mjg59]

A reasonably common design for applications that want to run code at a specific time is something like:

time_t wakeup_time = get_next_event_time();
time_t now = time(NULL);
sleep(wakeup_time-now);

This works absolutely fine, except that sleep() ignores time spent with a suspended system. If you sleep(3600) and then immediately suspend for 45 minutes you'll wake up after 105 minutes, not 60. Which probably isn't what you want. If you want a timer that'll expire at a specific time (or immediately after resume if that time passed during suspend), use the POSIX timer family (timer_create, timer_settime and friends) with CLOCK_REALTIME. It's a signal-driven interface rather than a blocking one, so implementation may be a little more complicated, but it has the advantage of actually working.

Comments

[(Anonymous)]

What is the argument that "realtime" should not just be the intuitive "real wall-clock time that normal people normally care about"?

[mjg59]

What's the argument that it should be? It's a spec. You're supposed to have clearly defined terms. We can argue that Linux's current behaviour is in violation, but we can't clearly demonstrate that.

[(Anonymous)]

I would think that 'realtime' in the spec says real time, not computer experienced time.