From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <4B72EA44.2090706@domain.hid>
Date: Wed, 10 Feb 2010 18:17:56 +0100
From: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
MIME-Version: 1.0
References: <4B72DB97.1020203@domain.hid> <4B72DF9F.9090103@domain.hid>
	<4B72E0D3.50004@domain.hid> <4B72E428.6000606@domain.hid>
	<4B72E7E8.2050603@domain.hid>
In-Reply-To: <4B72E7E8.2050603@domain.hid>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Subject: Re: [Xenomai-core] xnselect_destroy fails to wake up waiters
List-Id: Xenomai life and development <xenomai.xenomai.org>
List-Unsubscribe: <https://mail.gna.org/listinfo/xenomai-core>,
	<mailto:xenomai-core-request@domain.hid>
List-Archive: </public/xenomai-core>
List-Post: <mailto:xenomai@xenomai.org>
List-Help: <mailto:xenomai-core-request@domain.hid>
List-Subscribe: <https://mail.gna.org/listinfo/xenomai-core>,
	<mailto:xenomai-core-request@domain.hid>
To: Jan Kiszka <jan.kiszka@domain.hid>
Cc: xenomai-core <xenomai@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 b=
lock
>>>>> on select until some other event arrives. That's unfortunately not
>>>>> standard conforming.
>>>> Ok. Got it, I was mixing xnselect_destroy and xnselector_destroy. Ye=
s,
>>>> 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.
>=20
> "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 th=
e
> 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 na=C3=AFv=
e
implementation would result in the closed fd being constantly signaled
and select no longer blocking.

--=20
					    Gilles.