Re: [Xenomai-core] xnselect_destroy fails to wake up waiters

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Jan Kiszka wrote:
> 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.)"

Ok. But I need to think a bit for a correct implementation. The naïve
implementation would result in the closed fd being constantly signaled
and select no longer blocking.

-- 
					    Gilles.