* net/tramp-adb.el: Spell author name correctly.
[emacs.git] / lisp / userlock.el
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1 ;;; userlock.el --- handle file access contention between multiple users
3 ;; Copyright (C) 1985-1986, 2001-2014 Free Software Foundation, Inc.
5 ;; Author: Richard King
6 ;; (according to authors.el)
7 ;; Maintainer: emacs-devel@gnu.org
8 ;; Keywords: internal
9 ;; Package: emacs
11 ;; This file is part of GNU Emacs.
13 ;; GNU Emacs is free software: you can redistribute it and/or modify
14 ;; it under the terms of the GNU General Public License as published by
15 ;; the Free Software Foundation, either version 3 of the License, or
16 ;; (at your option) any later version.
18 ;; GNU Emacs is distributed in the hope that it will be useful,
19 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
20 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
21 ;; GNU General Public License for more details.
23 ;; You should have received a copy of the GNU General Public License
24 ;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>.
26 ;;; Commentary:
28 ;; This file is autoloaded to handle certain conditions
29 ;; detected by the file-locking code within Emacs.
30 ;; The two entry points are `ask-user-about-lock' and
31 ;; `ask-user-about-supersession-threat'.
33 ;;; Code:
35 (define-error 'file-locked "File is locked" 'file-error)
37 ;;;###autoload
38 (defun ask-user-about-lock (file opponent)
39 "Ask user what to do when he wants to edit FILE but it is locked by OPPONENT.
40 This function has a choice of three things to do:
41 do (signal 'file-locked (list FILE OPPONENT))
42 to refrain from editing the file
43 return t (grab the lock on the file)
44 return nil (edit the file even though it is locked).
45 You can redefine this function to choose among those three alternatives
46 in any way you like."
47 (discard-input)
48 (save-window-excursion
49 (let (answer short-opponent short-file)
50 (setq short-file
51 (if (> (length file) 22)
52 (concat "..." (substring file (- (length file) 22)))
53 file))
54 (setq short-opponent
55 (if (> (length opponent) 25)
56 (save-match-data
57 (string-match " (pid [0-9]+)" opponent)
58 (concat (substring opponent 0 13) "..."
59 (match-string 0 opponent)))
60 opponent))
61 (while (null answer)
62 (message "%s locked by %s: (s, q, p, ?)? "
63 short-file short-opponent)
64 (let ((tem (let ((inhibit-quit t)
65 (cursor-in-echo-area t))
66 (prog1 (downcase (read-char))
67 (setq quit-flag nil)))))
68 (if (= tem help-char)
69 (ask-user-about-lock-help)
70 (setq answer (assoc tem '((?s . t)
71 (?q . yield)
72 (?\C-g . yield)
73 (?p . nil)
74 (?? . help))))
75 (cond ((null answer)
76 (beep)
77 (message "Please type q, s, or p; or ? for help")
78 (sit-for 3))
79 ((eq (cdr answer) 'help)
80 (ask-user-about-lock-help)
81 (setq answer nil))
82 ((eq (cdr answer) 'yield)
83 (signal 'file-locked (list file opponent)))))))
84 (cdr answer))))
86 (defun ask-user-about-lock-help ()
87 (with-output-to-temp-buffer "*Help*"
88 (princ "It has been detected that you want to modify a file that someone else has
89 already started modifying in Emacs.
91 You can <s>teal the file; the other user becomes the
92 intruder if (s)he ever unmodifies the file and then changes it again.
93 You can <p>roceed; you edit at your own (and the other user's) risk.
94 You can <q>uit; don't modify this file.")
95 (with-current-buffer standard-output
96 (help-mode))))
98 (define-error 'file-supersession nil 'file-error)
100 ;;;###autoload
101 (defun ask-user-about-supersession-threat (fn)
102 "Ask a user who is about to modify an obsolete buffer what to do.
103 This function has two choices: it can return, in which case the modification
104 of the buffer will proceed, or it can (signal 'file-supersession (file)),
105 in which case the proposed buffer modification will not be made.
107 You can rewrite this to use any criterion you like to choose which one to do.
108 The buffer in question is current when this function is called."
109 (discard-input)
110 (save-window-excursion
111 (let ((prompt
112 (format "%s changed on disk; \
113 really edit the buffer? (y, n, r or C-h) "
114 (file-name-nondirectory fn)))
115 (choices '(?y ?n ?r ?? ?\C-h))
116 answer)
117 (while (null answer)
118 (setq answer (read-char-choice prompt choices))
119 (cond ((memq answer '(?? ?\C-h))
120 (ask-user-about-supersession-help)
121 (setq answer nil))
122 ((eq answer ?r)
123 ;; Ask for confirmation if buffer modified
124 (revert-buffer nil (not (buffer-modified-p)))
125 (signal 'file-supersession
126 (list "File reverted" fn)))
127 ((eq answer ?n)
128 (signal 'file-supersession
129 (list "File changed on disk" fn)))))
130 (message
131 "File on disk now will become a backup file if you save these changes.")
132 (setq buffer-backed-up nil))))
134 (defun ask-user-about-supersession-help ()
135 (with-output-to-temp-buffer "*Help*"
136 (princ "You want to modify a buffer whose disk file has changed
137 since you last read it in or saved it with this buffer.
139 If you say `y' to go ahead and modify this buffer,
140 you risk ruining the work of whoever rewrote the file.
141 If you say `r' to revert, the contents of the buffer are refreshed
142 from the file on disk.
143 If you say `n', the change you started to make will be aborted.
145 Usually, you should type `n' and then `M-x revert-buffer',
146 to get the latest version of the file, then make the change again.")
147 (with-current-buffer standard-output
148 (help-mode))))
150 ;;; userlock.el ends here