OpenEuphoria

Re: Multitasking: active waiting!?

• Posted by Jason Gade <jaygade at yahoo.com> Apr 19, 2006
• 475 views

Ryan W. Johnson wrote:
> 
> Robert Craig wrote:
>  
> > The way it works at the moment, the Euphoria task scheduler 
> > calls sleep() only when there is a gap of at least 1 second
> > until the next task is due to resume. That's because sleep() only
> > has a resolution of 1 second (that's the worst case 
> > across all platforms). For smaller gaps it just spins its 
> > wheels in a loop. 
> 
> That's what i thought was happening.
> 
> > It might be wasteful to sleep for a tiny fraction of a second, 
> > giving up control, and hoping the O/S will give it back in time. 
> > Also, other than DOS, the O/S should be able to grab control 
> > pre-emptively whenever it wants to run another process, 
> > regardless of whether you are sleeping or not.
> 
> The problem I have with that is the program is hogging all the available CPU
> instead of letting the CPU idle. It's true that the OS can still give other
> processes a chance to run, but the point is it's not letting the CPU idle like
> it should be when it's not "doing" anything.
> 
> I'm wondering how well it would work if the scheduler tried to sleep for short
> intervals (perhaps 0.01 s).
> 
> Here's an idea: if you made the sleep() procedure more precise, then the
> programmer could easily create an
> idle task. 
> 
> }}}
<eucode>
> global procedure idle(atom idletime)
>    while 1 do
>       sleep(idletime)
>       task_yield()
>    end while
> end procedure
> 
> task_idle = task_create(routine_id("idle"), {0.01}) --create task to idle for
> 0.01 seconds.
> task_schedule(task_idle, {1}) --time-shared task
> </eucode>
{{{

> 
> "Real-time tasks have a higher priority. Time-shared tasks are run when no
> real-time
> task is ready to execute."
> If i understand this correctly, the above code would call the task_idle() only
> when real-time tasks are not scheduled to run, right?
> 
> If you think it's a good idea, perhaps idle() could even be a built-in
> routine.
> What do you think about all this, Rob?
> 
> ~Ryan W. Johnson
> 
> Fluid Application Environment
> <a href="http://www.fluidae.com/">http://www.fluidae.com/</a>
> 
> [cool quote here, if i ever think of one...]

I think the tasking would work best for programs that always needed to be doing
something.

If a program needed to do nothing for awhile, then call task_clock_stop() for as
long as it needs to wait. Then restart tasking when it needs to.

--
"Any programming problem can be solved by adding a level of indirection."
--anonymous
"Any performance problem can be solved by removing a level of indirection."
--M. Haertel
"Premature optimization is the root of all evil in programming."
--C.A.R. Hoare
j.