Implement CLASH_DETECTION for MS-Windows.

 src/filelock.c [WINDOWSNT]: Include w32.h.
 (MAKE_LOCK_NAME): Don't use 'lock', it clashes with MS runtime
 function of that name.  Up-case the macro arguments.
 (IS_LOCK_FILE): New macro.
 (fill_in_lock_file_name): Use IS_LOCK_FILE instead of S_ISLNK.
 (create_lock_file): New function, with body extracted from
 lock_file_1.
 [WINDOWSNT]: Implement lock files by writing a regular file with
 the lock information as its contents.
 (read_lock_data): New function, on Posix platforms just calls
 emacs_readlinkat.
 [WINDOWSNT]: Read the lock info from the file.
 (current_lock_owner): Call read_lock_data instead of calling
 emacs_readlinkat directly.
 (lock_file) [WINDOWSNT]: Run the file name through
 dostounix_filename.
 src/w32proc.c (sys_kill): Support the case of SIG = 0, in which case
 just check if the process by that PID exists.
 src/w32.c (sys_open): Don't reset the _O_CREAT flag if _O_EXCL is
 also present, as doing so will fail to error out if the file
 already exists.
 src/makefile.w32-in ($(BLD)/filelock.$(O)): Depend on src/w32.h.

 nt/inc/ms-w32.h (BOOT_TIME_FILE): Define.
 nt/config.nt (CLASH_DETECTION): Define to 1.

 lisp/emacs-lisp/bytecomp.el (byte-recompile-directory): Reject files
 that match "\`\.#", to avoid compiling lock files, even if they
 are readable (as they are on MS-Windows).

 doc/emacs/files.texi (Interlocking): Don't refer to symlinks as the
 exclusive means of locking files.

 etc/NEWS: Mention support for lock files on MS-Windows.

1 files changed, 7 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 07f52adb2b1..7d1110d5dc6 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -348,6 +348,13 @@ Setting it has no effect, and %t in the mode-line format is ignored.
 Likewise, `file-name-buffer-file-type-alist' is now obsolete, and
 modifying it has no effect.
 
+---
+** Lock files now work on MS-Windows.
+This allows to avoid losing your edits if the same file is being
+edited in another Emacs session or by another user.  See the node
+"Interlocking" in the Emacs User Manual for the details.  To disable
+file locking, customize `create-lockfiles' to nil.
+
 ** Improved fullscreen support on Mac OS X.
 Both native (>= OSX 10.7) and "old style" fullscreen are supported.
 Customize `ns-use-native-fullscreen' to change style.  For >= 10.7