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From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: Jeff King <peff@peff.net>
Cc: git@vger.kernel.org, "Junio C Hamano" <gitster@pobox.com>,
	"Thomas Rast" <tr@thomasrast.ch>,
	"Phil Haack" <haacked@gmail.com>,
	"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"Stefan Beller" <sbeller@google.com>,
	"Jason Frey" <jfrey@redhat.com>,
	"Philip Oakley" <philipoakley@iee.org>
Subject: Re: [PATCH 8/9] git_config_set: use do_config_from_file() directly
Date: Fri, 30 Mar 2018 16:01:56 +0200 (DST)	[thread overview]
Message-ID: <nycvar.QRO.7.76.6.1803301558360.5026@qfpub.tvgsbejvaqbjf.bet> (raw)
In-Reply-To: <20180330131456.GB29568@sigill.intra.peff.net>

Hi Peff,

On Fri, 30 Mar 2018, Jeff King wrote:

> On Fri, Mar 30, 2018 at 03:02:00PM +0200, Johannes Schindelin wrote:
> 
> > > I'm not sure I understand that last paragraph. What does flockfile() have
> > > to do with stdin/stdout?
> > > 
> > > The point of those calls is that we're locking the FILE handle, so that
> > > it's safe for the lower-level config code to run getc_unlocked(), which
> > > is faster.
> > > 
> > > So without those, we're calling getc_unlocked() without holding the
> > > lock. I think it probably works in practice because we know that we're
> > > single-threaded, but it seems a bit sketchy.
> > 
> > Oops. I misunderstood the purpose of flockfile(), then. I thought it was
> > only about multiple users of stdin/stdout.
> > 
> > Will have a look whether flockfile()/funlockfile() can be moved into
> > do_config_from_file() instead.
> 
> In a sense stdin/stdout are much more susceptible to this because
> they're global variables, and any thread may touch them. For the config
> code, we open our own handle that we don't expose elsewhere. So probably
> it would be fine just to use the unlocked variants even without locking.
> 
> But IMHO it's good practice to always flockfile() before using the
> unlocked variants. My reading of POSIX is that it's OK to use the
> unlocked variants without holding the lock (if you know there won't be
> contention), but if it's not hard to err on the side of safety, I'd
> prefer it.

You know what is *really* funny?

-- snip --
static int git_config_from_stdin(config_fn_t fn, void *data)
{
        return do_config_from_file(fn, CONFIG_ORIGIN_STDIN, "", NULL, stdin, data, 0);
}

int git_config_from_file(config_fn_t fn, const char *filename, void *data)
{
        int ret = -1;
        FILE *f;

        f = fopen_or_warn(filename, "r");
        if (f) {
                flockfile(f);
                ret = do_config_from_file(fn, CONFIG_ORIGIN_FILE, filename, filename, f, data, 0);
                funlockfile(f);
                fclose(f);
        }
        return ret;
}
-- snap --

So the _stdin variant *goes out of its way not to flockfile()*...

But I guess all this will become moot when I start handing down the config
options. It does mean that I have to change the signatures in header
files, oh well ;-)

But then I can drop this here patch and we can stop musing about
flockfile()  ;-)

Ciao,
Dscho

  reply	other threads:[~2018-03-30 14:02 UTC|newest]

Thread overview: 103+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-29 15:18 [PATCH 0/9] Assorted fixes for `git config` (including the "empty sections" bug) Johannes Schindelin
2018-03-29 15:18 ` [PATCH 1/9] git_config_set: fix off-by-two Johannes Schindelin
2018-03-29 18:15   ` Stefan Beller
2018-03-29 19:41     ` Jeff King
2018-03-30 12:32       ` Johannes Schindelin
2018-03-30 14:15         ` Ævar Arnfjörð Bjarmason
2018-03-30 16:24           ` Junio C Hamano
2018-03-30 18:44             ` Johannes Schindelin
2018-03-30 19:00               ` Junio C Hamano
2018-04-03  9:31                 ` Johannes Schindelin
2018-04-03 15:29                   ` Duy Nguyen
2018-04-03 15:47                     ` Johannes Schindelin
2018-04-08 23:12                   ` Junio C Hamano
2018-03-30 16:36         ` Duy Nguyen
2018-03-30 18:53           ` Johannes Schindelin
2018-03-30 19:16             ` Duy Nguyen
2018-03-30 18:45         ` A potential approach to making tests faster on Windows Ævar Arnfjörð Bjarmason
2018-03-30 18:58           ` Junio C Hamano
2018-03-30 19:16           ` Jeff King
2018-04-03  9:49             ` Johannes Schindelin
2018-04-03 11:28               ` Ævar Arnfjörð Bjarmason
2018-04-03 15:55                 ` Johannes Schindelin
2018-04-03 21:36               ` Eric Sunshine
2018-04-03 11:43           ` Johannes Schindelin
2018-04-03 13:27             ` Jeff King
2018-04-03 16:00               ` Johannes Schindelin
2018-04-06 21:40                 ` Jeff King
2018-04-06 21:57                   ` Stefan Beller
2018-03-29 15:18 ` [PATCH 2/9] t1300: rename it to reflect that `repo-config` was deprecated Johannes Schindelin
2018-03-29 19:42   ` Jeff King
2018-03-30 12:37     ` Johannes Schindelin
2018-03-29 15:18 ` [PATCH 3/9] t1300: avoid relying on a bug Johannes Schindelin
2018-03-29 19:43   ` Jeff King
2018-03-30 12:38     ` Johannes Schindelin
2018-03-29 15:18 ` [PATCH 4/9] t1300: remove unreasonable expectation from TODO Johannes Schindelin
2018-03-29 19:52   ` Jeff King
2018-03-29 20:45     ` Junio C Hamano
2018-03-30 12:42     ` Johannes Schindelin
2018-03-29 15:18 ` [PATCH 5/9] t1300: `--unset-all` can leave an empty section behind (bug) Johannes Schindelin
2018-03-29 19:54   ` Jeff King
2018-03-29 15:18 ` [PATCH 6/9] git_config_set: simplify the way the section name is remembered Johannes Schindelin
2018-03-29 15:19 ` [PATCH 7/9] git config --unset: remove empty sections (in normal situations) Johannes Schindelin
2018-03-29 21:32   ` Jeff King
2018-03-30 13:00     ` Johannes Schindelin
2018-03-30 13:09       ` Jeff King
2018-03-29 15:19 ` [PATCH 8/9] git_config_set: use do_config_from_file() directly Johannes Schindelin
2018-03-29 21:38   ` Jeff King
2018-03-30 13:02     ` Johannes Schindelin
2018-03-30 13:14       ` Jeff King
2018-03-30 14:01         ` Johannes Schindelin [this message]
2018-03-30 14:08           ` Jeff King
2018-03-30 19:04             ` Johannes Schindelin
2018-03-29 15:19 ` [PATCH 9/9] git_config_set: reuse empty sections Johannes Schindelin
2018-03-29 21:50   ` Jeff King
2018-03-30 13:15     ` Johannes Schindelin
2018-03-29 17:58 ` [PATCH 0/9] Assorted fixes for `git config` (including the "empty sections" bug) Stefan Beller
2018-03-30 12:14   ` Johannes Schindelin
2018-03-29 19:39 ` Jeff King
2018-03-30 12:35   ` Johannes Schindelin
2018-03-30 14:17 ` Ævar Arnfjörð Bjarmason
2018-03-30 18:46   ` Johannes Schindelin
2018-04-03 16:27 ` [PATCH v2 00/15] " Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 01/15] git_config_set: fix off-by-two Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 02/15] t1300: rename it to reflect that `repo-config` was deprecated Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 03/15] t1300: demonstrate that --replace-all can "invent" newlines Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 04/15] config --replace-all: avoid extra line breaks Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 05/15] t1300: avoid relying on a bug Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 06/15] t1300: remove unreasonable expectation from TODO Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 07/15] t1300: `--unset-all` can leave an empty section behind (bug) Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 08/15] config: introduce an optional event stream while parsing Johannes Schindelin
2018-04-06 21:22     ` Jeff King
2018-04-09  7:35       ` Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 09/15] config: avoid using the global variable `store` Johannes Schindelin
2018-04-06 21:23     ` Jeff King
2018-04-09  7:36       ` Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 10/15] config_set_store: rename some fields for consistency Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 11/15] git_config_set: do not use a state machine Johannes Schindelin
2018-04-06 21:28     ` Jeff King
2018-04-09  7:50       ` Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 12/15] git_config_set: make use of the config parser's event stream Johannes Schindelin
2018-04-03 16:28   ` [PATCH v2 13/15] git config --unset: remove empty sections (in the common case) Johannes Schindelin
2018-04-03 16:29   ` [PATCH v2 14/15] git_config_set: reuse empty sections Johannes Schindelin
2018-04-03 16:30   ` [PATCH v2 00/15] Assorted fixes for `git config` (including the "empty sections" bug) Johannes Schindelin
2018-04-06 21:33   ` Jeff King
2018-04-09  8:19     ` Johannes Schindelin
2018-04-09  8:31   ` [PATCH v3 " Johannes Schindelin
2018-04-09  8:31     ` [PATCH v3 01/15] git_config_set: fix off-by-two Johannes Schindelin
2018-04-09  8:31     ` [PATCH v3 02/15] t1300: rename it to reflect that `repo-config` was deprecated Johannes Schindelin
2018-04-09  8:31     ` [PATCH v3 03/15] t1300: demonstrate that --replace-all can "invent" newlines Johannes Schindelin
2018-04-09  8:31     ` [PATCH v3 04/15] config --replace-all: avoid extra line breaks Johannes Schindelin
2018-04-09  8:31     ` [PATCH v3 05/15] t1300: avoid relying on a bug Johannes Schindelin
2018-04-09  8:31     ` [PATCH v3 06/15] t1300: remove unreasonable expectation from TODO Johannes Schindelin
2018-04-09  8:31     ` [PATCH v3 07/15] t1300: add a few more hairy examples of sections becoming empty Johannes Schindelin
2018-04-09  8:32     ` [PATCH v3 08/15] t1300: `--unset-all` can leave an empty section behind (bug) Johannes Schindelin
2018-04-09  8:32     ` [PATCH v3 09/15] config: introduce an optional event stream while parsing Johannes Schindelin
2018-04-09  8:32     ` [PATCH v3 10/15] config: avoid using the global variable `store` Johannes Schindelin
2018-04-09  8:32     ` [PATCH v3 11/15] config_set_store: rename some fields for consistency Johannes Schindelin
2018-04-09  8:32     ` [PATCH v3 12/15] git_config_set: do not use a state machine Johannes Schindelin
2018-04-09  8:32     ` [PATCH v3 13/15] git_config_set: make use of the config parser's event stream Johannes Schindelin
2018-05-08 13:42       ` Jeff King
2018-05-08 14:00         ` Jeff King
2018-04-09  8:32     ` [PATCH v3 14/15] git config --unset: remove empty sections (in the common case) Johannes Schindelin
2018-04-09  8:32     ` [PATCH v3 15/15] git_config_set: reuse empty sections Johannes Schindelin

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