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From: Ben Gamari <ben@smart-cactus.org>
To: emacs-devel@gnu.org
Cc: Ben Gamari <ben@smart-cactus.org>,
	21559@debbugs.gnu.org, michael.albinus@gmx.de
Subject: bug#21559: [PATCH] autorevert: Wait a while before calling vc-find-file-hook
Date: Mon, 26 Oct 2015 19:43:38 +0100	[thread overview]
Message-ID: <1445885018-17451-2-git-send-email-ben__31073.4246545055$1445885089$gmane$org@smart-cactus.org> (raw)
In-Reply-To: <1445885018-17451-1-git-send-email-ben@smart-cactus.org>

This provides a resolution for Bug #21559.

emacs running with `auto-revert-mode` enabled breaks `git rebase` in
repositories where files are open. The problem appears to be that
`auto-revert-mode` attempts to refresh version control information with
`vc-find-file-hook` on revert events. `vc-find-file-hook` calls out to
`git`, taking the repository's index lock.

This interferes badly with `git rebase`, which performs many git
commands in quick succession. When `auto-revert-mode` is enabled there
is a very high chance that the following race will occur,

    git                                  emacs
    ----------------------               -----------------------------
    1. git rebase checks out
       a commit, releases
       `index.lock`
                                         2. `auto-revert-mode` notices
                                            change, firing off a `git`
                                            process and taking
`index.lock`.

    3. git rebase applies patch
       and attempts to commit.
       Notices that `index.lock`
       is taken and fails.

                                         4. emacs' `git` process
                                            finishes, releasing lock

In the end the user is left with a badly broken rebase process and an
error message complaining that `index.lock` exists, which he then goes
to confirm and finds no such file as emacs has already released the
lock.

We work around this by scheduling a worker to call `vc-fine-file-hook`
at some point in the future when the repository is more likely to be
idle (for instance, when there have been no change events for a second
or so).

Signed-Off-By: Ben Gamari <ben@smart-cactus.org>
---
 lisp/autorevert.el | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/lisp/autorevert.el b/lisp/autorevert.el
index 37ee8ee..0c25ac3 100644
--- a/lisp/autorevert.el
+++ b/lisp/autorevert.el
@@ -136,6 +136,11 @@ auto-revert-tail-mode
 (defvar auto-revert-timer nil
   "Timer used by Auto-Revert Mode.")
 
+(defvar auto-revert-vc-check-timer nil
+  "Timer used by Auto-Revert Mode to schedule
+checks of version control information. See
+`auto-revert-schedule-vc-check' for details.")
+
 (defcustom auto-revert-interval 5
   "Time, in seconds, between Auto-Revert Mode file checks.
 The value may be an integer or floating point number.
@@ -260,6 +265,13 @@ auto-revert-check-vc-info
   :type 'boolean
   :version "22.1")
 
+(defcustom auto-revert-vc-check-idle-time 2
+  "How much time to wait after noticing a changed file before calling
+`vc-find-file-hook' or nil to check immediately."
+  :group 'auto-revert
+  :type 'number
+  :version "25.1")
+
 (defvar-local global-auto-revert-ignore-buffer nil
   "When non-nil, Global Auto-Revert Mode will not revert this buffer.
 This variable becomes buffer local when set in any fashion.")
@@ -671,7 +683,28 @@ auto-revert-handler
     ;; `preserve-modes' avoids changing the (minor) modes.  But we do
     ;; want to reset the mode for VC, so we do it manually.
     (when (or revert auto-revert-check-vc-info)
-      (vc-find-file-hook))))
+      (auto-revert-schedule-vc-check))))
+
+(defun auto-revert-schedule-vc-check ()
+  "Schedule a call to `vc-find-file-hook'.
+
+We need to be careful when calling `vc-find-file-hook' after file changes
+as some version control utilities (e.g. git rebase) have a tendency
+to do many successive calls and will fail ungracefully if they find
+we have taken the repository lock.
+
+For this reason we wait for the repository to be idle for at least
+`auto-revert-vc-check-idle-time' seconds before calling
+`vc-find-file-hook'."
+  (if auto-revert-vc-check-idle-time
+      (progn
+        (when (timerp auto-revert-vc-check-timer)
+          (cancel-timer auto-revert-vc-check-timer))
+        (setq auto-revert-vc-check-idle-timer
+              (run-at-time auto-revert-vc-check-idle-time nil
+                           'vc-find-file-hook))
+        )
+    (vc-find-file-hook)))
 
 (defun auto-revert-tail-handler (size)
   (let ((modified (buffer-modified-p))
-- 
2.6.1






  reply	other threads:[~2015-10-26 18:43 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-09-25 12:45 bug#21559: 25.0.50; auto-revert-mode breaks git rebase Ben Gamari
2015-09-26  7:41 ` Eli Zaretskii
2015-09-28 14:11   ` Ben Gamari
2015-09-28 14:35     ` Eli Zaretskii
2015-09-28 15:05       ` Ben Gamari
2015-09-29  8:47     ` Michael Albinus
2015-10-26 18:43 ` bug#21559: [PATCH] autorevert: Wait for repository to become idle before calling vc-find-file-hook Ben Gamari
2015-10-26 18:43   ` Ben Gamari [this message]
2015-10-27  8:25     ` bug#21559: [PATCH] autorevert: Wait a while " Michael Albinus
2015-10-28 11:59       ` Ben Gamari
2015-10-28 14:45         ` Michael Albinus
2015-10-28 17:05           ` Ben Gamari
2015-10-29  8:20             ` Michael Albinus
2016-02-06  0:01 ` bug#21559: 25.0.50; auto-revert-mode breaks git rebase Mitchel Humpherys
2016-02-06 12:34   ` Ben Gamari
2016-02-07  1:34     ` Mitchel Humpherys
2016-02-07  5:03       ` Mitchel Humpherys
2016-02-07  5:21         ` Mitchel Humpherys
2016-02-07 10:22           ` Ben Gamari
2016-02-07 10:55             ` Ben Gamari
2016-02-07 17:06               ` Mitchel Humpherys
2016-02-07 17:22                 ` Ben Gamari
2016-02-08 21:19               ` Daniel Colascione
2016-09-09 20:56 ` Jason Merrill
2018-02-14 10:08 ` Alexei Khlebnikov
2018-02-15 19:08   ` Alexei Khlebnikov
2018-02-15 22:32     ` Alexei Khlebnikov
2018-02-19 23:41     ` Dmitry Gutov
2018-02-20  0:06       ` Alexei Khlebnikov
2018-02-20  0:17         ` Dmitry Gutov
2018-02-20  4:07           ` Eli Zaretskii
2018-02-20  7:40       ` Michael Albinus
2018-02-20 11:37         ` Dmitry Gutov
2018-02-20 11:53           ` Michael Albinus
2018-02-20 22:28             ` Dmitry Gutov
2018-02-21 22:07               ` Alexei Khlebnikov
2018-02-22 11:24                 ` Michael Albinus
2018-02-22 11:45                   ` Dmitry Gutov
2018-02-19 10:24 ` bug#21559: PATCH review needed: lisp/vc/vc-git.el (vc-git-state, vc-git-conflicted-files) Alexei Khlebnikov
2018-02-19 12:39   ` Michael Albinus
2018-02-19 15:29   ` Eli Zaretskii
2018-02-19 18:39     ` Alexei Khlebnikov
2018-02-19 18:50       ` Michael Albinus
2018-02-19 19:05         ` Alexei Khlebnikov
2018-02-19 23:35         ` Dmitry Gutov
2018-09-25 12:23 ` bug#21559: additional patch needed to set GIT_OPTIONAL_LOCKS=0 in all cases Andrew Ruder
2018-09-26  3:16   ` Phil Sainty
2018-09-26  9:45     ` Michael Albinus
2018-09-29 11:16       ` Michael Albinus

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