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Date: Wed, 10 Feb 2010 18:07:52 +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:
>> 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.
>>> Ok. Got it, I was mixing xnselect_destroy and xnselector_destroy. Yes,
>>> right, something should be done. What is supposed to happen? Is it
>>> supposed to be signaled as an exceptional condition?
>>>
>> It should be signaled so that the caller tries to read/write/whatever
>> and then gets the information that the fd is down.
> 
> Looks to me like you get a wakeup for nothing... From the spec:
> http://www.opengroup.org/onlinepubs/009695399/functions/select.html
> 
> I do not see anything specified for the fds closure.

"A descriptor shall be considered ready for reading when a call to an
input function with O_NONBLOCK clear would not block, whether or not the
function would transfer data successfully. (The function might return
data, an end-of-file indication, or an error other than one indicating
that it is blocked, and in each of these cases the descriptor shall be
considered ready for reading.)"

Jan

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