🚀 go-pugleaf

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  >>>>> El Wed, 07 Feb 2001 13:16:26 +0100, "Eduardo Ferro"
  >>>>> nos contaba en es.comp.os.linux.programacion:

>caso es que tengo que ahcer una driver para mi empresa y me etoy
>volviendo loco intentando implementar un timeout, a la espera de una
>interrupci�n, es decir quiero quedarme durmiendo hasta que pase una de
>las dos cosas, se produzca una interrupci�n, o se llegue al timeout.
>
>El caso es que las dos cosas por separado ya las he hecho en otros
>driver mediante schedule_timeout e interruptible_sleep_on, pero me
>estoy volviendo loco para ver como esperar las dos cosas a la vez.

    Esta semana se ha hablado de estas cosas en el kernel. He sacado
esto de LWN. Es la forma correcta(tm) de hacerlo *para un solo* evento.
Pero me imagino que es la base para hacerlo con dos o m�s...

  
Date:   Wed, 31 Jan 2001 09:14:30 +0000 (GMT)
From:   David Woodhouse <dwmw2@infradead.org>
To:     Timur Tabi <ttabi@interactivesi.com>
Subject: Re: [ANNOUNCE] Kernel Janitor's TODO list

On Tue, 30 Jan 2001, Timur Tabi wrote:

> > If you have a task that looks like:
> >
> >     loop:
> >         <do something important>
> >         sleep_on(q)
> >
> > And you do wakeup(q) hoping to get something important done, then if the
> > task isn't sleeping at the time of the wakeup it will ignore the wakeup
> > and go to sleep, which imay not be what you wanted.
>
> Ok, so how should this code have been written?

DECLARE_WAIT_QUEUE(wait, current);

while(1) {
        do_something_important()

        set_current_state(TASK_INTERRUPTIBLE);
        add_wait_queue(&q, &wait);

        /* Now if something arrives, we'll be 'woken' immediately -
           - that is; our state will be set to TASK_RUNNING */

        if (!stuff_to_do()) {
                /* If the 'stuff' arrives here, we get woken anyway,
                        so the schedule() returns immediately. You
                        can use schedule_timeout() here if you need
                        a timeout, obviously */
                schedule();
        }

        set_current_state(TASK_RUNNING);
        remove_wait_queue(&q, &wait);

        if (signal_pending(current)) {
                /* You've been signalled. Deal with it. If you don't
                        want signals to wake you, use TASK_UNINTERRUPTIBLE
                        above instead of TASK_INTERRUPTIBLE. Be aware
                        that you'll add one to the load average all the
                        time your task is sleeping then. */
                return -EINTR;
        }
}


Alternatively, you could up() a semaphore for each task that's do be done,
and down() it again each time you remove one from the queue.

 --
dwmw2


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                                       Saludos de Javier Cantero
                                    (jcantero at escomposlinux.org)


- -- 
"Yo uso Software Libre" (declaraci�n a petici�n de Richard M. Stallman)

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