Re: repeat a function after fixed time period

[linux-os]

On Wed, 23 Mar 2005, Arjan van de Ven wrote:

> > This kernel code should do just fine.
> >
> >
> >
> > struct INFO {
> >      struct timer_list timer;            // For test timer
> >      atomic_t running;                   // Timer is running
> >      };
> >
> > //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> > //
> > //   This stops the timer. This must NOT be called with a spin-lock
> > //   held.
> > //
> > static void stop_timer()
> > {
> >      if(atomic_read(&info->running))
> >      {
> >          atomic_dec(&info->running);
>
> this is a race.

No, never. stop_timer() can be called at any time, even from
interrupt context. The last guy to touch info->running wins.
The logic works just perfectly.

> >          if(info->timer.function)
> >              del_timer(&info->timer);
>
> you probably want del_timer_sync() here.
>
>
> > static void start_timer(void)
> > {
> >      if(!atomic_read(&info->running))
> >      {
> >          atomic_inc(&info->running);
>
> same race.

No such race at all.


>

Cheers,
Dick Johnson
Penguin : Linux version 2.6.11 on an i686 machine (5537.79 BogoMips).
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