Hourglass - how is it started and ended?

[Lennart Borgman]

I got a bit irritated that Emacs did not stop to show an hourglass after an
operation ended so I looked into the code. However while trying to find the
code for this I first stumbled on some other problems. I have some
difficulties to understand the code for starting the hourglass cursor:

1) There is a function start_hourglass. This starts a timer that turns on
the hourglass. The function start_hourglass begins with cancel_hourglass
which cancels the timer if it is already active and removes the hourglass if
it is shown. Why is it useful to begin with this? I would expect
start_hourglass to just do nothing if the hourglass was already shown (and
perhaps also if the timer was active). Can anyone please explain this?

2) In w32fns.c start_hourglass has a "#if 0" around the whole body part. Is
this actually run?? (The hourglass is shown on w32.)