All of lore.kernel.org
 help / color / mirror / Atom feed
From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: Duy Nguyen <pclouds@gmail.com>
Cc: David Turner <dturner@twopensource.com>,
	Git Mailing List <git@vger.kernel.org>
Subject: Re: [PATCH 18/19] index-helper: autorun
Date: Fri, 18 Mar 2016 16:57:07 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.20.1603181656160.4690@virtualbox> (raw)
In-Reply-To: <CACsJy8Bu6QyYmJpPHpEgDx5djt=9XjXzckzJKL_mx8yHeyHdCA@mail.gmail.com>

Hi Duy,

On Fri, 18 Mar 2016, Duy Nguyen wrote:

> On Fri, Mar 18, 2016 at 2:17 PM, Johannes Schindelin
> <Johannes.Schindelin@gmx.de> wrote:
> >
> > On Fri, 18 Mar 2016, Duy Nguyen wrote:
> >
> >> > Well, the way I read the code it is possible that:
> >> >
> >> > 1. Git process 1 starts, reading the index
> >> > 2. Git process 2 starts, poking the index-helper
> >> > 3. The index-helper updates the .pid file (why not set a bit in the shared
> >> >    memory?) with a prefix "W"
> >> > 4. Git process 2 reads the .pid file and waits for the "W" to go away
> >> >    (what if index-helper is not fast enough to write the "W"?)
> >> > 5. Git process 1 access the index, happily oblivious that it is being
> >> >    updated and the data is in an inconsistent state
> >>
> >> No, if process 1 reads the index file, then that file will remain
> >> consistent/unchanged all the time. index-helper is not allowed to
> >> touch that file at all.
> >>
> >> The process 2 gets the index content from shm (cached by the index
> >> helper), verifies that it's good (with the signature at the end of the
> >> shm). If watchman is used, process 2 can also read the list of
> >> modified files from another shm, combine it with the in-core index,
> >> then write it down the normal way. Only then process 1 (or process 3)
> >> can see the new index content from the file.
> >
> > So how do you deal with releasing the shared memory instances that are
> > essentially created for every index update?
> 
> When index-helper reads the index file and realizes the file has been
> updated (based on trailing SHA-1), it unlink()s the old shm and
> prepares new shm. If no process is accessing old shm, it's gone. If
> not, it stays until nobody elses uses it. shm on Windows behaves the
> same way, I believe.

Ah. On Windows, you do not even have to unlink: once the last user's gone,
the shared memory's gone, too.

Ciao,
Dscho

  reply	other threads:[~2016-03-18 15:57 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-09 18:36 [PATCH 00/19] index-helper, watchman David Turner
2016-03-09 18:36 ` [PATCH 01/19] trace.c: add GIT_TRACE_PACK_STATS for pack usage statistics David Turner
2016-03-09 22:58   ` Junio C Hamano
2016-03-10  0:05     ` David Turner
2016-03-10 10:59       ` Duy Nguyen
2016-03-09 18:36 ` [PATCH 02/19] read-cache.c: fix constness of verify_hdr() David Turner
2016-03-09 18:36 ` [PATCH 03/19] read-cache: allow to keep mmap'd memory after reading David Turner
2016-03-09 23:02   ` Junio C Hamano
2016-03-10  0:09     ` David Turner
2016-03-09 18:36 ` [PATCH 04/19] index-helper: new daemon for caching index and related stuff David Turner
2016-03-09 23:09   ` Junio C Hamano
2016-03-09 23:21     ` Junio C Hamano
2016-03-10  0:01       ` David Turner
2016-03-10 11:17       ` Duy Nguyen
2016-03-10 20:22         ` David Turner
2016-03-11  1:11           ` Duy Nguyen
2016-03-10  0:18     ` David Turner
2016-03-15 11:56     ` Duy Nguyen
2016-03-15 15:56       ` Junio C Hamano
2016-03-15 11:52   ` Duy Nguyen
2016-03-09 18:36 ` [PATCH 05/19] trace.c: add GIT_TRACE_INDEX_STATS for index statistics David Turner
2016-03-09 18:36 ` [PATCH 06/19] index-helper: add --strict David Turner
2016-03-09 18:36 ` [PATCH 07/19] daemonize(): set a flag before exiting the main process David Turner
2016-03-09 18:36 ` [PATCH 08/19] index-helper: add --detach David Turner
2016-03-09 18:36 ` [PATCH 09/19] index-helper: add Windows support David Turner
2016-03-16 11:42   ` Duy Nguyen
2016-03-17 12:18     ` Johannes Schindelin
2016-03-17 12:59       ` Duy Nguyen
2016-03-09 18:36 ` [PATCH 10/19] read-cache: add watchman 'WAMA' extension David Turner
2016-03-09 18:36 ` [PATCH 11/19] Add watchman support to reduce index refresh cost David Turner
2016-03-09 18:36 ` [PATCH 12/19] read-cache: allow index-helper to prepare shm before git reads it David Turner
2016-03-09 18:36 ` [PATCH 13/19] index-helper: use watchman to avoid refreshing index with lstat() David Turner
2016-03-09 18:36 ` [PATCH 14/19] update-index: enable/disable watchman support David Turner
2016-03-09 18:36 ` [PATCH 15/19] unpack-trees: preserve index extensions David Turner
2016-03-09 18:36 ` [PATCH 16/19] index-helper: rewrite pidfile after daemonizing David Turner
2016-03-09 18:36 ` [PATCH 17/19] index-helper: process management David Turner
2016-03-09 18:36 ` [PATCH 18/19] index-helper: autorun David Turner
2016-03-15 12:12   ` Duy Nguyen
2016-03-15 14:26     ` Johannes Schindelin
2016-03-16 11:37       ` Duy Nguyen
2016-03-16 18:11       ` David Turner
2016-03-16 18:27         ` Johannes Schindelin
2016-03-17 13:02           ` Duy Nguyen
2016-03-17 14:43             ` Johannes Schindelin
2016-03-17 18:31               ` David Turner
2016-03-18  0:50               ` Duy Nguyen
2016-03-18  7:14                 ` Johannes Schindelin
2016-03-18  7:44                   ` Duy Nguyen
2016-03-18 17:22                     ` David Turner
2016-03-18 23:09                       ` Duy Nguyen
2016-03-18  7:17                 ` Johannes Schindelin
2016-03-18  7:34                   ` Duy Nguyen
2016-03-18 15:57                     ` Johannes Schindelin [this message]
2016-03-09 18:36 ` [PATCH 19/19] hack: watchman/untracked cache mashup David Turner
2016-03-15 12:31   ` Duy Nguyen
2016-03-17  0:56     ` David Turner
2016-03-17 13:06       ` Duy Nguyen
2016-03-17 18:08         ` David Turner
2016-03-29 17:09 ` [PATCH 00/19] index-helper, watchman Torsten Bögershausen
2016-03-29 21:51   ` David Turner

Reply instructions:

You may reply publicly 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

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

  git send-email \
    --in-reply-to=alpine.DEB.2.20.1603181656160.4690@virtualbox \
    --to=johannes.schindelin@gmx.de \
    --cc=dturner@twopensource.com \
    --cc=git@vger.kernel.org \
    --cc=pclouds@gmail.com \
    /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
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.