X-Recipient: archive-cygwin AT delorie DOT com
X-SWARE-Spam-Status: No, hits=-1.3 required=5.0 	tests=AWL,BAYES_00,SARE_MSGID_LONG40,SPF_PASS
X-Spam-Check-By: sourceware.org
MIME-Version: 1.0
In-Reply-To: <20090312221723.GA9322@calimero.vinschen.de>
References: <9e3fd2c80903120740u5fa06d62t372cd67212fad1e AT mail DOT gmail DOT com> 	 <20090312155236 DOT GX9322 AT calimero DOT vinschen DOT de> 	 <9e3fd2c80903120944h5aebc094y7e461eee580e4eeb AT mail DOT gmail DOT com> 	 <20090312221723 DOT GA9322 AT calimero DOT vinschen DOT de>
Date: Fri, 13 Mar 2009 08:36:03 +0100
Message-ID: <9e3fd2c80903130036v7898622fuca6f83d8c0080837@mail.gmail.com>
Subject: Re: Problem getting flock with timeout to work
From: Robert Klemme <shortcutter AT googlemail DOT com>
To: cygwin AT cygwin DOT com
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
X-IsSubscribed: yes
Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm
Precedence: bulk
List-Id: <cygwin.cygwin.com>
List-Unsubscribe: <mailto:cygwin-unsubscribe-archive-cygwin=delorie DOT com AT cygwin DOT com>
List-Subscribe: <mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive: <http://sourceware.org/ml/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-help AT cygwin DOT com>, <http://sourceware.org/ml/#faqs>
Sender: cygwin-owner AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com
Delivered-To: mailing list cygwin AT cygwin DOT com

Corinna,

thanks for your feedback!

2009/3/12 Corinna Vinschen <corinna-cygwin AT cygwin DOT com>:
> On Mar 12 17:44, Robert Klemme wrote:
>> The second flock does not start the command as I expect it to be.
>>
>> I am referring to the man page of flock which says this about option -w:
>>
>> Fail =A0(with an exit code of 1) if the lock cannot be acquired within
>> seconds seconds. =A0Decimal fractional values are allowed.
>>
>> So, since the second flock obviously cannot obtain the lock in time, I
>> would have expected it to fail and not execute the command given.
>> This is at least a documentation issue as flock's behavior and
>> documentation do not match IMHO.
>
> This scenario (your first testcase) works fine with Cygwin 1.7 with my
> fix from a couple of hours ago. =A0I missed the fact that BSD flock lock
> semantic allows to set both lock types (LOCK_SH/LOCK_EX) regardless of
> the read/write mode in which the file has been opened, in contrast
> to POSIX lock semantic. =A0That's fixed now and other than that glitch,
> it worked.

Hey, that's good news!

> However...

> Cygwin won't be able to support the scenario from your second testcase
> for the time being. =A0The reason is that in this scenario
>
> =A0(
> =A0 =A0flock -s 200
> =A0 =A0...
> =A0) 200> lockfile
>
> the lock will end when the flock process exits. =A0The lock can only
> persist as long as the process which created the lock, or any of the
> child applications which inherited the file descriptor, still runs. =A0We
> can't maintain a global file descriptor table with lock information like
> the OS or what a master process could do if Cygwin would be designed so.

Thank you for the explanation!

> I know that's bad news, it certainly is for me since I thought I had
> implemented flock with full BSD semantics, but we just can't do that
> for now.

For me this is good enough - I find the variant "flock -c" better anyway. :=
-)

Thank you for looking into this!  Sorry for the intermediate confusion
about your "wrong" Linux.

Kind regards

robert

--
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
Problem reports:       http://cygwin.com/problems.html
Documentation:         http://cygwin.com/docs.html
FAQ:                   http://cygwin.com/faq/