From: Daniel Shahaf <d.s@daniel.shahaf.name>
To: Bart Schaefer <schaefer@brasslantern.com>
Cc: "zsh-workers@zsh.org" <zsh-workers@zsh.org>,
Martin Tournoij <martin@arp242.net>
Subject: Re: Any way to allow clobbering empty files when noclobber is set?
Date: Sat, 6 Jun 2020 08:03:03 +0000 [thread overview]
Message-ID: <20200606080303.0ab42262@tarpaulin.shahaf.local2> (raw)
In-Reply-To: <CAH+w=7YqAiOdd4sAbSRxghp3RD_qQjfR5V8jT-KhhOOppysv1A@mail.gmail.com>
Bart Schaefer wrote on Sat, 06 Jun 2020 00:08 -0700:
> On Fri, Jun 5, 2020 at 9:55 PM Daniel Shahaf <d.s@daniel.shahaf.name> wrote:
> >
> > Bart Schaefer wrote on Fri, 05 Jun 2020 18:41 -0700:
> > >
> > > I don't think that's the intended typical usage of noclobber. It's
> > > not set by default, and it can't have any effect outside the local
> > > shell.
> >
> > NO_CLOBBER causes open() to be called with the O_EXCL bit, which does
> > affect other processes as well.
>
> ?? All that O_EXCL guarantees is that no other process is able to
> create the file. Once it exists, another file can open it and
> truncate it and write to it, unless prevented by umask.
But in Roman's example, _both_ backgrouned processes use O_EXCL, so
whichever process loses the race will get an error when it calls
open(2). Yes, attempts to open() the file without O_EXCL will succeed,
but when a file is used as a mutex, everyone who tries to open the file
will try to use O_EXCL.
Makes sense?
Cheers,
Daniel
next prev parent reply other threads:[~2020-06-06 8:03 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20200603020919eucas1p13e26ebcbb335784d14bfb97b137f385a@eucas1p1.samsung.com>
2020-06-03 2:08 ` Martin Tournoij
2020-06-03 12:04 ` Peter Stephenson
2020-06-04 1:48 ` Daniel Shahaf
2020-06-04 2:43 ` Bart Schaefer
2020-06-04 4:06 ` Daniel Shahaf
2020-06-04 5:00 ` Bart Schaefer
2020-06-05 3:10 ` Daniel Shahaf
2020-06-05 3:18 ` Daniel Shahaf
2020-06-06 1:07 ` Bart Schaefer
2020-06-06 4:48 ` Daniel Shahaf
2020-06-06 7:04 ` Bart Schaefer
2020-06-04 6:31 ` Martin Tournoij
2020-06-05 2:22 ` Daniel Shahaf
2020-06-04 2:13 ` Vin Shelton
2020-06-04 2:35 ` Bart Schaefer
2020-06-04 2:36 ` Daniel Shahaf
2020-06-04 11:57 ` Vin Shelton
2020-06-04 5:06 ` Bart Schaefer
2020-06-04 5:41 ` Roman Perepelitsa
2020-06-05 2:07 ` Daniel Shahaf
2020-06-05 4:38 ` Roman Perepelitsa
2020-06-06 1:41 ` Bart Schaefer
2020-06-06 4:55 ` Daniel Shahaf
2020-06-06 6:25 ` Roman Perepelitsa
2020-06-06 7:08 ` Bart Schaefer
2020-06-06 8:03 ` Daniel Shahaf [this message]
[not found] ` <1941572212.466119.1591360860372@mail2.virginmedia.com>
[not found] ` <e7f7dfe2-eb4a-457b-85fb-091935a74c0e@www.fastmail.com>
2020-06-06 11:57 ` Peter Stephenson
2020-06-06 12:48 ` Roman Perepelitsa
2020-06-06 15:24 ` Bart Schaefer
2020-06-06 16:24 ` Peter Stephenson
2020-06-07 11:55 ` Daniel Shahaf
2020-06-07 17:00 ` Peter Stephenson
2020-06-08 3:27 ` Daniel Shahaf
2020-06-08 9:30 ` Peter Stephenson
2020-06-07 17:20 ` Bart Schaefer
2020-06-06 15:09 ` Bart Schaefer
2020-06-04 6:47 ` Martin Tournoij
2020-06-04 9:42 ` Peter Stephenson
2020-06-04 12:20 ` Roman Perepelitsa
2020-06-04 12:26 ` Peter Stephenson
2020-06-04 12:15 ` Peter Stephenson
2020-06-04 20:35 ` Bart Schaefer
2020-06-05 1:59 ` Daniel Shahaf
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