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.

3 files changed, 19 insertions, 1 deletions

diff --git a/nt/ChangeLog b/nt/ChangeLog
index a8bb8c74c91..fab143fcddc 100644
--- a/nt/ChangeLog
+++ b/nt/ChangeLog
@@ -1,3 +1,9 @@
+2013-02-25  Eli Zaretskii  <eliz@gnu.org>
+
+        * inc/ms-w32.h (BOOT_TIME_FILE): Define.
+
+        * config.nt (CLASH_DETECTION): Define to 1.
+
 2013-02-16  Eli Zaretskii  <eliz@gnu.org>
 
         * inc/ms-w32.h (__STDC__): Fiddle with value only for MSVC.
diff --git a/nt/config.nt b/nt/config.nt
index 61e56174bb4..cc4e91d9af0 100644
--- a/nt/config.nt
+++ b/nt/config.nt
@@ -75,7 +75,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 /* Define if you want lock files to be written, so that Emacs can tell
    instantly when you try to modify a file that someone else has modified in
    his/her Emacs. */
-#undef CLASH_DETECTION
+#define CLASH_DETECTION 1
 
 /* Short copyright string for this version of Emacs. */
 #define COPYRIGHT "Copyright (C) 2013 Free Software Foundation, Inc."
diff --git a/nt/inc/ms-w32.h b/nt/inc/ms-w32.h
index 66f586a4f76..9473fbe3ca6 100644
--- a/nt/inc/ms-w32.h
+++ b/nt/inc/ms-w32.h
@@ -70,6 +70,18 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #define HAVE___BUILTIN_UNWIND_INIT 1
 #endif
 
+/* This isn't perfect, as some systems might have the page file in
+   another place.  Also, I suspect that the time stamp of that file
+   might also change when Windows enlarges the file due to
+   insufficient VM.  Still, this seems to be the most reliable way;
+   the alternative (of using GetSystemTimes) won't work on laptops
+   that hibernate, because the system clock is stopped then.  Other
+   possibility would be to run "net statistics workstation" and parse
+   the output, but that's gross.  So this should do; if the file is
+   not there, the boot time will be returned as zero, and filelock.c
+   already handles that.  */
+#define BOOT_TIME_FILE "C:/pagefile.sys"
+
 /* ============================================================ */
 
 /* Here, add any special hacks needed to make Emacs work on this