Windows ginput function [Was: fopen doesn't return when opening a fifo!!]

[David Bateman]

John W. Eaton wrote:
> On  2-Apr-2008, David Bateman wrote:
>
> | Then we need to have O_NONBLOCK set on the output pipe and use a while
> | loop to probe for input.. This wait loop in Octave will however
> | needlessly consume CPU cycles.. I have that version of the code as well
> | if you'd prefer.
>
> It is only in this loop while ginput is active, right?  What about
> sleeping for 0.1s each time through the loop?  Would that be
> acceptable?
>   
Yes its only in the wait loop when ginput is active. For sleeping to
reduce the CPU load it needs to be much longer than a time slice of the
processor. The HZ variable in the linux kernel sets this value to
typically 10ms. Therefore yes a 100ms sleep might reduce the CPU usage.
However in octave, sleep(0.1) will ultimately call the libc usleep
function, and this is implemented with a wait loop in any case. Try

while (true), usleep(0.1); end

and check the CPU load.. So doing this won't gain you anything.
Additionally what if the user is a fast clicker, and is faster than the
arbitrary 0.1s delay. This will result in missed clicks.. I therefore
thinks its better to not sleep, or use blocking reads.

I believe the attached patch should work as you'd like it to.

D.

-- 
David Bateman                                David.Bateman at motorola.com
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Parc Les Algorithmes, Commune de St Aubin    +33 6 72 01 06 33 (Mob) 
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