From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Wed, 10 Feb 2010 19:26:59 +0100
From: Jan Kiszka <jan.kiszka@domain.hid>
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Subject: Re: [Xenomai-core] xnselect_destroy fails to wake up waiters
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To: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
Cc: xenomai-core <xenomai@xenomai.org>

Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
>> Hi Gilles,
>>
>> I tend to think that xnselect_destroy should signal an event on the
>> dying fd instead of just clearing the binding. The task blocking on
>> select currently does not get a hint that the fd is dead and will block
>> on select until some other event arrives. That's unfortunately not
>> standard conforming.
> 
> Could you test the following patch? The fd will be in the "pending" set
> until the fd is reused, but that should be harmless as long as the fd is
> not in the "expected" set.
> 
> diff --git a/ksrc/nucleus/select.c b/ksrc/nucleus/select.c
> index fd56bfb..17c5e0b 100644
> --- a/ksrc/nucleus/select.c
> +++ b/ksrc/nucleus/select.c
> @@ -131,7 +131,8 @@ int xnselect_bind(struct xnselect *select_block,
>  		__FD_SET(index, &selector->fds[type].pending);
>  		if (xnselect_wakeup(selector))
>  			xnpod_schedule();
> -	}
> +	} else
> +		__FD_CLR(index, &selector->fds[type].pending);
>  
>  	return 0;
>  }
> @@ -178,6 +179,7 @@ EXPORT_SYMBOL_GPL(__xnselect_signal);
>  void xnselect_destroy(struct xnselect *select_block)
>  {
>  	xnholder_t *holder;
> +	int resched;
>  	spl_t s;
>  
>  	xnlock_get_irqsave(&nklock, s);
> @@ -190,11 +192,18 @@ void xnselect_destroy(struct xnselect *select_block)
>  
>  		__FD_CLR(binding->bit_index,
>  			 &selector->fds[binding->type].expected);
> -		__FD_CLR(binding->bit_index,
> -			 &selector->fds[binding->type].pending);
> +		if (!__FD_ISSET(binding->bit_index,
> +				&selector->fds[binding->type].pending)) {
> +			__FD_SET(binding->bit_index,
> +				 &selector->fds[binding->type].pending);
> +			if (xnselect_wakeup(selector))
> +				resched = 1;
> +		}
>  		removeq(&selector->bindings, &binding->slink);
>  		xnlock_put_irqrestore(&nklock, s);
>  
> +		if (resched)
> +			xnpod_schedule();
>  		xnfree(binding);
>  		
>  		xnlock_get_irqsave(&nklock, s);
> 

Works perfectly! You may test yourself using the RT-TCP examples from
latest RTnet git. :)

Thanks,
Jan

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