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[emacs.git] / lisp / userlock.el
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1 ;;; userlock.el --- handle file access contention between multiple users
3 ;; Copyright (C) 1985, 1986 Free Software Foundation, inc.
5 ;; Maintainer: FSF
6 ;; Keywords: internal
8 ;; This file is part of GNU Emacs.
10 ;; GNU Emacs is free software; you can redistribute it and/or modify
11 ;; it under the terms of the GNU General Public License as published by
12 ;; the Free Software Foundation; either version 2, or (at your option)
13 ;; any later version.
15 ;; GNU Emacs is distributed in the hope that it will be useful,
16 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
17 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 ;; GNU General Public License for more details.
20 ;; You should have received a copy of the GNU General Public License
21 ;; along with GNU Emacs; see the file COPYING. If not, write to the
22 ;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
23 ;; Boston, MA 02111-1307, USA.
25 ;;; Commentary:
27 ;; This file is autoloaded to handle certain conditions
28 ;; detected by the file-locking code within Emacs.
29 ;; The two entry points are `ask-user-about-lock' and
30 ;; `ask-user-about-supersession-threat'.
32 ;;; Code:
34 (put 'file-locked 'error-conditions '(file-locked file-error error))
36 ;;;###autoload
37 (defun ask-user-about-lock (fn opponent)
38 "Ask user what to do when he wants to edit FILE but it is locked by USER.
39 This function has a choice of three things to do:
40 do (signal 'buffer-file-locked (list FILE USER))
41 to refrain from editing the file
42 return t (grab the lock on the file)
43 return nil (edit the file even though it is locked).
44 You can rewrite it to use any criterion you like to choose which one to do."
45 (discard-input)
46 (save-window-excursion
47 (let (answer)
48 (while (null answer)
49 (message "%s is locking %s: action (s, q, p, ?)? " opponent fn)
50 (let ((tem (let ((inhibit-quit t)
51 (cursor-in-echo-area t))
52 (prog1 (downcase (read-char))
53 (setq quit-flag nil)))))
54 (if (= tem help-char)
55 (ask-user-about-lock-help)
56 (setq answer (assoc tem '((?s . t)
57 (?q . yield)
58 (?\C-g . yield)
59 (?p . nil)
60 (?? . help))))
61 (cond ((null answer)
62 (beep)
63 (message "Please type q, s, or p; or ? for help")
64 (sit-for 3))
65 ((eq (cdr answer) 'help)
66 (ask-user-about-lock-help)
67 (setq answer nil))
68 ((eq (cdr answer) 'yield)
69 (signal 'file-locked (list "File is locked" fn opponent)))))))
70 (cdr answer))))
72 (defun ask-user-about-lock-help ()
73 (with-output-to-temp-buffer "*Help*"
74 (princ "It has been detected that you want to modify a file that someone else has
75 already started modifying in EMACS.
77 You can <s>teal the file; The other user becomes the
78 intruder if (s)he ever unmodifies the file and then changes it again.
79 You can <p>roceed; you edit at your own (and the other user's) risk.
80 You can <q>uit; don't modify this file.")
81 (save-excursion
82 (set-buffer standard-output)
83 (help-mode))))
85 (put
86 'file-supersession 'error-conditions '(file-supersession file-error error))
88 ;;;###autoload
89 (defun ask-user-about-supersession-threat (fn)
90 "Ask a user who is about to modify an obsolete buffer what to do.
91 This function has two choices: it can return, in which case the modification
92 of the buffer will proceed, or it can (signal 'file-supersession (file)),
93 in which case the proposed buffer modification will not be made.
95 You can rewrite this to use any criterion you like to choose which one to do.
96 The buffer in question is current when this function is called."
97 (discard-input)
98 (save-window-excursion
99 (let (answer)
100 (while (null answer)
101 (message "%s changed on disk; really edit the buffer? (y, n, r or C-h) "
102 (file-name-nondirectory fn))
103 (let ((tem (downcase (let ((cursor-in-echo-area t))
104 (read-char)))))
105 (setq answer
106 (if (= tem help-char)
107 'help
108 (cdr (assoc tem '((?n . yield)
109 (?\C-g . yield)
110 (?y . proceed)
111 (?r . revert)
112 (?? . help))))))
113 (cond ((null answer)
114 (beep)
115 (message "Please type y, n or r; or ? for help")
116 (sit-for 3))
117 ((eq answer 'help)
118 (ask-user-about-supersession-help)
119 (setq answer nil))
120 ((eq answer 'revert)
121 (revert-buffer nil (not (buffer-modified-p)))
122 ; ask confirmation iff buffer modified
123 (signal 'file-supersession
124 (list "File reverted" fn)))
125 ((eq answer 'yield)
126 (signal 'file-supersession
127 (list "File changed on disk" fn))))))
128 (message
129 "File on disk now will become a backup file if you save these changes.")
130 (setq buffer-backed-up nil))))
132 (defun ask-user-about-supersession-help ()
133 (with-output-to-temp-buffer "*Help*"
134 (princ "You want to modify a buffer whose disk file has changed
135 since you last read it in or saved it with this buffer.
137 If you say `y' to go ahead and modify this buffer,
138 you risk ruining the work of whoever rewrote the file.
139 If you say `r' to revert, the contents of the buffer are refreshed
140 from the file on disk.
141 If you say `n', the change you started to make will be aborted.
143 Usually, you should type `n' and then `M-x revert-buffer',
144 to get the latest version of the file, then make the change again.")
145 (save-excursion
146 (set-buffer standard-output)
147 (help-mode))))
149 ;;; userlock.el ends here