Class RealClock

Initializes the real clock.

Arguments:
manager -- the resource manager
quantum -- interval between clock wakeups
fastforward -- if True, the clock won't actually sleep
               for the duration of the quantum.

Overrides: object.__init__

See docstring in base Clock class.

Overrides: Clock.get_time

See docstring in base Clock class.

Overrides: Clock.get_start_time

See docstring in base Clock class.

Overrides: Clock.get_next_schedulable_time

Runs the real clock through time.

The clock starts when run() is called. In each iteration of the main loop
it will do the following:
- Wake up the resource manager
- Determine if there will be anything to do before the next
  time the clock will wake up (after the quantum has passed). Note
  that this information is readily available on the slot table.
  If so, set next-wakeup-time to (now + time until slot table
  event). Otherwise, set it to (now + quantum)
- Sleep until next-wake-up-time

The clock keeps on tickin' until a SIGINT signal (Ctrl-C if running in the
foreground) or a SIGTERM signal is received.

Overrides: Clock.run

Handler for SIGTERM and SIGINT. Allows Haizea to stop gracefully.