git@vger.kernel.org mailing list mirror (one of many)
 help / Atom feed
From: Jeff King <peff@peff.net>
To: Michael Haggerty <mhagger@alum.mit.edu>
Cc: Brandon Williams <bmwill@google.com>,
	Lars Schneider <larsxschneider@gmail.com>,
	Martin Ågren <martin.agren@gmail.com>,
	Git Users <git@vger.kernel.org>
Subject: Re: [PATCH] config: use a static lock_file struct
Date: Sat, 2 Sep 2017 04:44:51 -0400
Message-ID: <20170902084451.h5pmbtolqcl2j3w4@sigill.intra.peff.net> (raw)
In-Reply-To: <8e09e4e1-984c-78d1-7b87-0bafe5346621@alum.mit.edu>

On Wed, Aug 30, 2017 at 09:07:53AM +0200, Michael Haggerty wrote:

> > So it's probably safer to just let tempfile.c handle the whole lifetime,
> > and have it put all live tempfiles on the heap, and free them when
> > they're deactivated. That means our creation signature becomes more
> > like:
> > 
> >   struct tempfile *create_tempfile(const char *path);
> > 
> > and delete_tempfile() actually calls free() on it (though we'd probably
> > want to skip the free() from a signal handler for the usual reasons).
> 
> I agree that the latter would be a nice, and relatively safe, design. It
> would involve some fairly intrusive changes to client code, though.
>
> I think it would be possible to implement the new API while leaving the
> old one intact, to avoid having to rewrite all clients at once, and
> potentially to allow clients to avoid a malloc if they already have a
> convenient place to embed a `struct tempfile` (except that now they'd be
> able to free it when done). For example, `create_tempfile(tempfile,
> path)` and its friends could accept NULL as the first argument, in which
> case it would malloc a `struct tempfile` itself, and mark it as being
> owned by the tempfile module. Such objects would be freed when
> deactivated. But if the caller passes in a non-NULL `tempfile` argument,
> the old behavior would be retained.

There are actually very few callers of create_tempfile (I count two).
Everybody just uses lock_file(). So I think we could get away with just
modifying the internals of the lock struct to hold a pointer, and then
teaching commit_lock_file() et al to reset it to NULL after performing
an operation that frees the tempfile. We could even modify
rename_tempfile() and friends to take a pointer-to-pointer and NULL it
itself. That would make it harder to get wrong.

In the long term I don't think there's a huge value to being able to
place a "struct tempfile" inside another struct, as opposed to holding a
pointer. It saves a malloc, but at the cost of opening up confusion
about lifetimes.

-Peff

  reply index

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-27  7:37 [PATCH] pkt-line: re-'static'-ify buffer in packet_write_fmt_1() Martin Ågren
2017-08-27 15:41 ` Jeff King
2017-08-27 18:25   ` Jeff King
2017-08-27 18:21 ` Lars Schneider
2017-08-27 19:09   ` Martin Ågren
2017-08-27 19:15     ` Jeff King
2017-08-27 20:04     ` Lars Schneider
2017-08-27 23:23       ` Jeff King
2017-08-28  4:11         ` Martin Ågren
2017-08-28 17:52           ` Stefan Beller
2017-08-28 17:58             ` Jeff King
2017-09-05 10:03               ` Junio C Hamano
2017-08-29 17:51           ` Lars Schneider
2017-08-29 18:53             ` Jeff King
2017-08-29 18:58               ` [PATCH] config: use a static lock_file struct Jeff King
2017-08-29 19:09                 ` Brandon Williams
2017-08-29 19:10                   ` Brandon Williams
2017-08-29 19:12                   ` Jeff King
2017-08-30  3:25                     ` Michael Haggerty
2017-08-30  4:31                       ` Jeff King
2017-08-30  4:55                         ` Michael Haggerty
2017-08-30  4:55                         ` Jeff King
2017-08-30  5:55                           ` Jeff King
2017-08-30  7:07                             ` Michael Haggerty
2017-09-02  8:44                               ` Jeff King [this message]
2017-09-02 13:50                                 ` Jeff King
2017-08-30  6:55                           ` Michael Haggerty
2017-08-30 19:53                             ` Jeff King
2017-08-30 19:57                               ` Brandon Williams
2017-08-30 20:11                                 ` Jeff King
2017-08-30 21:06                                   ` Brandon Williams
2017-08-31  4:09                                     ` Jeff King
2017-09-06  3:59                 ` Junio C Hamano
2017-09-06 12:41                   ` Jeff King
2017-08-29 19:22               ` [PATCH] pkt-line: re-'static'-ify buffer in packet_write_fmt_1() Martin Ågren
2017-08-29 21:48                 ` Jeff King
2017-08-30  5:31                   ` Jeff King
2017-09-05 10:03                     ` Junio C Hamano
2017-10-10  4:06                       ` [PATCH 0/2] Do not call cmd_*() as a subroutine Junio C Hamano
2017-10-10  4:06                         ` [PATCH 1/2] describe: do not use " Junio C Hamano
2017-10-10 13:43                           ` SZEDER Gábor
2017-10-11  6:00                             ` Junio C Hamano
2017-10-10  4:06                         ` [PATCH 2/2] merge-ours: " Junio C Hamano

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: http://vger.kernel.org/majordomo-info.html

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20170902084451.h5pmbtolqcl2j3w4@sigill.intra.peff.net \
    --to=peff@peff.net \
    --cc=bmwill@google.com \
    --cc=git@vger.kernel.org \
    --cc=larsxschneider@gmail.com \
    --cc=martin.agren@gmail.com \
    --cc=mhagger@alum.mit.edu \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

git@vger.kernel.org mailing list mirror (one of many)

Archives are clonable:
	git clone --mirror https://public-inbox.org/git
	git clone --mirror http://ou63pmih66umazou.onion/git
	git clone --mirror http://czquwvybam4bgbro.onion/git
	git clone --mirror http://hjrcffqmbrq6wope.onion/git

Newsgroups are available over NNTP:
	nntp://news.public-inbox.org/inbox.comp.version-control.git
	nntp://ou63pmih66umazou.onion/inbox.comp.version-control.git
	nntp://czquwvybam4bgbro.onion/inbox.comp.version-control.git
	nntp://hjrcffqmbrq6wope.onion/inbox.comp.version-control.git
	nntp://news.gmane.org/gmane.comp.version-control.git

 note: .onion URLs require Tor: https://www.torproject.org/
       or Tor2web: https://www.tor2web.org/

AGPL code for this site: git clone https://public-inbox.org/ public-inbox