--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lisp/userlock.el	Mon Aug 13 11:28:15 2007 +0200
@@ -0,0 +1,241 @@
+;;; userlock.el --- handle file access contention between multiple users
+
+;; Copyright (C) 1985, 1986, 1993 Free Software Foundation, inc.
+
+;; Maintainer: FSF
+;; Keywords: internal
+
+;; This file is part of XEmacs.
+
+;; XEmacs is free software; you can redistribute it and/or modify it
+;; under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 2, or (at your option)
+;; any later version.
+
+;; XEmacs is distributed in the hope that it will be useful, but
+;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;; General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with XEmacs; see the file COPYING.  If not, write to the Free
+;; Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+;; 02111-1307, USA.
+
+;;; Synched up with: FSF 19.34.
+
+;;; Commentary:
+
+;; This file is autoloaded to handle certain conditions
+;; detected by the file-locking code within XEmacs.
+;; The two entry points are `ask-user-about-lock' and
+;; `ask-user-about-supersession-threat'.
+
+;;; Code:
+
+(define-error 'file-locked "File is locked" 'file-error) ; XEmacs
+
+(defun ask-user-about-lock-minibuf (fn opponent)
+  (save-window-excursion
+    (let (answer)
+      (while (null answer)
+	(message "%s is locking %s: action (s, q, p, ?)? " opponent fn)
+	(let ((tem (let ((inhibit-quit t)
+			 (cursor-in-echo-area t))
+		     (prog1 (downcase (read-char))
+		            (setq quit-flag nil)))))
+	  (if (= tem help-char)
+	      (ask-user-about-lock-help)
+	    (setq answer (assoc tem '((?s . t)
+				      (?q . yield)
+				      (?\C-g . yield)
+				      (?p . nil)
+				      (?? . help))))
+	    (cond ((null answer)
+		   (beep)
+		   (message "Please type q, s, or p; or ? for help")
+		   (sit-for 3))
+		  ((eq (cdr answer) 'help)
+		   (ask-user-about-lock-help)
+		   (setq answer nil))
+		  ((eq (cdr answer) 'yield)
+		   (signal 'file-locked (list "File is locked" fn opponent)))))))
+      (cdr answer))))
+
+(defun ask-user-about-lock-help ()
+  (with-output-to-temp-buffer "*Help*"
+    (princ "It has been detected that you want to modify a file that someone else has
+already started modifying in EMACS.
+
+You can <s>teal the file; The other user becomes the
+  intruder if (s)he ever unmodifies the file and then changes it again.
+You can <p>roceed; you edit at your own (and the other user's) risk.
+You can <q>uit; don't modify this file.")
+    (save-excursion
+      (set-buffer standard-output)
+      (help-mode))))
+
+(define-error 'file-supersession "File changed on disk" 'file-error) ; XEmacs
+
+(defun ask-user-about-supersession-threat-minibuf (fn)
+  (save-window-excursion
+    (let (answer)
+      (while (null answer)
+	(message "%s changed on disk; really edit the buffer? (y, n, r or C-h) "
+                 (file-name-nondirectory fn))
+	(let ((tem (downcase (let ((cursor-in-echo-area t))
+			       (read-char)))))
+	  (setq answer
+		(if (= tem help-char)
+		    'help
+		  (cdr (assoc tem '((?n . yield)
+				    (?\C-g . yield)
+				    (?y . proceed)
+				    (?r . revert)
+				    (?? . help))))))
+	  (cond ((null answer)
+		 (beep)
+		 (message "Please type y, n or r; or ? for help")
+		 (sit-for 3))
+		((eq answer 'help)
+		 (ask-user-about-supersession-help)
+		 (setq answer nil))
+		((eq answer 'revert)
+		 (revert-buffer nil (not (buffer-modified-p)))
+		 ; ask confirmation iff buffer modified
+		 (signal 'file-supersession
+			 (list "File reverted" fn)))
+		((eq answer 'yield)
+		 (signal 'file-supersession
+			 (list "File changed on disk" fn))))))
+      (message
+        "File on disk now will become a backup file if you save these changes.")
+      (setq buffer-backed-up nil))))
+
+(defun ask-user-about-supersession-help ()
+  (with-output-to-temp-buffer "*Help*"
+    (princ "You want to modify a buffer whose disk file has changed
+since you last read it in or saved it with this buffer.
+
+If you say `y' to go ahead and modify this buffer,
+you risk ruining the work of whoever rewrote the file.
+If you say `r' to revert, the contents of the buffer are refreshed
+from the file on disk.
+If you say `n', the change you started to make will be aborted.
+
+Usually, you should type `n' and then `M-x revert-buffer',
+to get the latest version of the file, then make the change again.")
+    (save-excursion
+      (set-buffer standard-output)
+      (help-mode))))
+
+;;; dialog-box versions [XEmacs]
+
+(defun ask-user-about-lock-dbox (fn opponent)
+  (let ((echo-keystrokes 0)
+	(dbox
+	 (cons
+	  (format "%s is locking %s\n
+	It has been detected that you want to modify a file that
+	someone else has already started modifying in XEmacs."
+		  opponent fn)
+	  '(["Steal Lock\n\nThe other user will\nbecome the intruder" steal t]
+	    ["Proceed\n\nEdit file at your own\n\(and the other user's) risk"
+	     proceed t]
+	    nil
+	    ["Abort\n\nDon't modify the buffer\n" yield t]))))
+    (popup-dialog-box dbox)
+    (catch 'aual-done
+      (while t
+	(let ((event (next-command-event)))
+	  (cond ((and (misc-user-event-p event) (eq (event-object event) 'proceed))
+		 (throw 'aual-done nil))
+		((and (misc-user-event-p event) (eq (event-object event) 'steal))
+		 (throw 'aual-done t))
+		((and (misc-user-event-p event) (eq (event-object event) 'yield))
+		 (signal 'file-locked (list "File is locked" fn opponent)))
+		((and (misc-user-event-p event)
+		      (eq (event-object event) 'menu-no-selection-hook))
+		 (signal 'quit nil))
+		((button-release-event-p event) ;; don't beep twice
+		 nil)
+		(t
+		 (beep)
+		 (message "please answer the dialog box"))))))))
+
+(defun ask-user-about-supersession-threat-dbox (fn)
+  (let ((echo-keystrokes 0)
+	(dbox
+	 (cons
+	  (format "File %s has changed on disk
+since its buffer was last read in or saved.
+
+Do you really want to edit the buffer? " fn)
+	  '(["Yes\n\nEdit the buffer anyway,\nignoring the disk file"
+	     proceed t]
+	    ["No\n\nDon't modify the buffer\n" yield t]
+	    nil
+	    ["No\n\nDon't modify the buffer\nbut revert it" revert t]
+	    ))))
+    (popup-dialog-box dbox)
+    (catch 'auast-done
+      (while t
+	(let ((event (next-command-event)))
+	  (cond ((and (misc-user-event-p event) (eq (event-object event) 'proceed))
+		 (throw 'auast-done nil))
+		((and (misc-user-event-p event) (eq (event-object event) 'yield))
+		 (signal 'file-supersession (list fn)))
+		((and (misc-user-event-p event) (eq (event-object event) 'revert))
+		 (or (equal fn (buffer-file-name))
+		     (error
+		      "ask-user-about-supersession-threat called bogusly"))
+		 (revert-buffer nil t)
+		 (signal 'file-supersession
+			 (list fn "(reverted)")))
+		((and (misc-user-event-p event)
+		      (eq (event-object event) 'menu-no-selection-hook))
+		 (signal 'quit nil))
+		((button-release-event-p event) ;; don't beep twice
+		 nil)
+		(t
+		 (beep)
+		 (message "please answer the dialog box"))))))))
+
+
+;;; top-level
+
+;;;###autoload
+(defun ask-user-about-lock (fn opponent)
+  "Ask user what to do when he wants to edit FILE but it is locked by USER.
+This function has a choice of three things to do:
+  do (signal 'file-locked (list FILE USER))
+    to refrain from editing the file
+  return t (grab the lock on the file)
+  return nil (edit the file even though it is locked).
+You can rewrite it to use any criterion you like to choose which one to do."
+  (discard-input)
+  (if (and (fboundp 'popup-dialog-box)
+	   (or (button-press-event-p last-command-event)
+	       (button-release-event-p last-command-event)
+	       (misc-user-event-p last-command-event)))
+      (ask-user-about-lock-dbox fn opponent)
+    (ask-user-about-lock-minibuf fn opponent)))
+
+;;;###autoload
+(defun ask-user-about-supersession-threat (fn)
+  "Ask a user who is about to modify an obsolete buffer what to do.
+This function has two choices: it can return, in which case the modification
+of the buffer will proceed, or it can (signal 'file-supersession (file)),
+in which case the proposed buffer modification will not be made.
+
+You can rewrite this to use any criterion you like to choose which one to do.
+The buffer in question is current when this function is called."
+  (discard-input)
+  (if (and (fboundp 'popup-dialog-box)
+	   (or (button-press-event-p last-command-event)
+	       (button-release-event-p last-command-event)
+	       (misc-user-event-p last-command-event)))
+      (ask-user-about-supersession-threat-dbox fn)
+    (ask-user-about-supersession-threat-minibuf fn)))
+
+;;; userlock.el ends here