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Subject:	Re: How efficient is 'sleep'?
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To:	Backwoods BC <completely DOT and DOT totally DOT trash AT gmail DOT com>, cygwin AT cygwin DOT com
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From:	Eliot Moss via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	Eliot Moss <moss AT cs DOT umass DOT edu>
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On 12/15/2023 4:55 PM, Backwoods BC via Cygwin wrote:
> I have quite a few "service-like" scripts that I put into the
> background and then have them wake up on a regular basis to do
> something. I use 'sleep' for the timing of the wakeup periods.
> 
> My question is: How efficient is 'sleep'? I know of other OSes that
> just set a timer flag and the process isn't allocated any CPU time
> until the timer expires.
> 
> I know that creating a service or even using Task Scheduler are more
> "proper" ways of doing this, but they are also much more work and
> would require a significant learning curve as my background is
> embedded systems, not Windows. I know that my lazy way probably has a
> penalty, but just how bad is it?
> 
> Thanks

You could strace on it to see what system calls it makes, but I am
pretty sure it sets up a timer interrupt and then waits for an event.
Very efficient.  It does not, for example, continually read the clock
until the requested amount of time has passed.

The more interesting question is this.  If you coded something like:

while true; do x; sleep 60; done

are you ok with x starting more than 60 seconds apart, because the time
to execute x itself, to fork and wait for the processes, etc., gets added
into each iteration?  If you prefer the invocations of x start at the start
of each minute, then you need to calculate, on each iteration, how long to
sleep.  There's loads of info on this stackoverflow page:

https://stackoverflow.com/questions/645992/sleep-until-a-specific-time-date

Cheers - Eliot Moss

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