Mailing-List: contact cygwin-help AT sourceware DOT cygnus DOT com; run by ezmlm
List-Subscribe: <mailto:cygwin-subscribe AT sources DOT redhat DOT com>
List-Archive: <http://sources.redhat.com/ml/cygwin/>
List-Post: <mailto:cygwin AT sources DOT redhat DOT com>
List-Help: <mailto:cygwin-help AT sources DOT redhat DOT com>, <http://sources.redhat.com/ml/#faqs>
Sender: cygwin-owner AT sources DOT redhat DOT com
Delivered-To: mailing list cygwin AT sources DOT redhat DOT com
Message-Id: <200108211525.KAA28846@devmail.dev.tivoli.com>
X-Mailer: exmh version 2.5 07/13/2001 with nmh-1.0.4
To: cygwin AT cygwin DOT com
Reply-To: jheyman AT dev DOT tivoli DOT com
Subject: Re: Help on posix file lock semantics 
In-reply-to: <20010820232542.A6414@ping.be> 
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Date: Tue, 21 Aug 2001 11:25:22 -0400
From: (Jerry Heyman) <jerry AT dev DOT tivoli DOT com>


I'm joining this late, and may be misunderstanding 
something, but...

On 20 August 2001 at 23:25, Kurt Roeckx <Q AT ping DOT be> wrote:
> On Mon, Aug 20, 2001 at 10:55:54PM +0200, Gunnar Andre Dalsnes wrote:
> > >On Sun, Aug 19, 2001 at 11:06:13PM +0200, Gunnar Andre Dalsnes wrote:
>> Example:
>> A file has write lock from off. 10 to 20 and read lock from off. 30 to 40.
>> A new read lock from off. 15 to 35 upgrades both existing overlapped 
regions.
>> 
>> Now we have three locks?
>> -write lock off. 10 to 15
>> -read lock off. 15 to 35
>> -read lock off. 35 to 40
>> 
>> Or maybe they merged? 
>> -write lock off. 10 to 15
>> -read lock off. 15 to 40
>> 
>> The reason i ask is that i want F_GETLK to behave correctly if called 
>> afterwards.
> 
> You got me there. :)
> 
> I don't see anything in the standard that covers it, so I guess
> it's implementation defined.
> 
> Otoh, is it really that important?

My understanding on the locks is that a Read lock is a downgrade
relative to a write lock.  A write lock is exclusive, and while a
read lock precludes others from writing, it doesn't preclude others
from reading.

With that assumption, you cannot merge and shrink the write lock,
but you would surely join the two read locks into a single lock.

jerry
-- 
Jerry Heyman   919.224.1442    | IBM SWG/Tivoli Software |"Software is the 
Build Infrastructure Architect | 3901 S Miami Blvd       | difference between
jheyman AT dev DOT tivoli DOT com         | Durham, NC  27703       | hardware and 
reality"
                          http://www.acm.org/~heymanj



--
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
Bug reporting:         http://cygwin.com/bugs.html
Documentation:         http://cygwin.com/docs.html
FAQ:                   http://cygwin.com/faq/