Re: File Locking Question

From:
Nigel Wade <nmw@ion.le.ac.uk>
Newsgroups:
comp.lang.java.programmer
Date:
Tue, 17 Jul 2007 09:28:51 +0100
Message-ID:
<f7huk2$qei$1@south.jnrs.ja.net>
alejandrina wrote:

On Jul 14, 10:08 pm, Arne Vajh??j <a...@vajhoej.dk> wrote:

Lew wrote:

Arne Vajh??j wrote:

#Whether or not a lock actually prevents another program from
#accessing the content of the locked region is system-dependent and
#therefore unspecified. The native file-locking facilities of some
#systems are merely advisory, meaning that programs must cooperatively
#observe a known locking protocol in order to guarantee data integrity.
#On other systems native file locks are mandatory, meaning that if one
#program locks a region of a file then other programs are actually
#prevented from accessing that region in a way that would violate the
#lock. On yet other systems, whether native file locks are advisory or
#mandatory is configurable on a per-file basis. To ensure consistent and
#correct behavior across platforms, it is strongly recommended that the
#locks provided by this API be used as if they were advisory locks.


Hey, that's the exact same quote that Oliver Wong cited when he answered
the OP's OP!


No surprise in that.

I guess Oliver believe in the Java Doc too.

Arne


I'll try to summarize what we know so far:

(a) FileLock seems to work across JVMs within a single client, but not
within a single JVM.
(b) "Across JVMs" in my problem means "across clients". The code I
posted
works in Windows (I think because the Windows file system can
enforce a file lock request) and also in Unix "where Unix advisory
locking works, which
apparently generally *doesn't* include NFS" .

We'll do some admin work on the Linux server and report back.

Thanks all!


This is purely a suggestion for you to research, it's not something I've ever
done myself. I have no idea if it will work any better or reliably than NFS
locking.

How about using SMB/Samba rather than NFS to export/mount your filesystems?
Cursory reading suggests that Samba supports the same file locking mechanisms
which Windows does.
http://samba.org/samba/docs/man/Samba-HOWTO-Collection/locking.html

--
Nigel Wade, System Administrator, Space Plasma Physics Group,
            University of Leicester, Leicester, LE1 7RH, UK
E-mail : nmw@ion.le.ac.uk
Phone : +44 (0)116 2523548, Fax : +44 (0)116 2523555

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