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.

2 files changed, 17 insertions, 12 deletions

diff --git a/doc/emacs/ChangeLog b/doc/emacs/ChangeLog
index 33f530cbadc..44245441791 100644
--- a/doc/emacs/ChangeLog
+++ b/doc/emacs/ChangeLog
@@ -1,3 +1,8 @@
+2013-02-25  Eli Zaretskii  <eliz@gnu.org>
+
+        * files.texi (Interlocking): Don't refer to symlinks as the
+        exclusive means of locking files.
+
 2013-02-22  Glenn Morris  <rgm@gnu.org>
 
         * ack.texi (Acknowledgments):
diff --git a/doc/emacs/files.texi b/doc/emacs/files.texi
index 7f7ae483cd5..1f78747eaa6 100644
--- a/doc/emacs/files.texi
+++ b/doc/emacs/files.texi
@@ -734,10 +734,10 @@ file.
 @cindex locking files
   When you make the first modification in an Emacs buffer that is
 visiting a file, Emacs records that the file is @dfn{locked} by you.
-(It does this by creating a specially-named symbolic link in the same
-directory.)  Emacs removes the lock when you save the changes.  The
-idea is that the file is locked whenever an Emacs buffer visiting it
-has unsaved changes.
+(It does this by creating a specially-named symbolic link or regular
+file with special contents in the same directory.)  Emacs removes the
+lock when you save the changes.  The idea is that the file is locked
+whenever an Emacs buffer visiting it has unsaved changes.
 
 @vindex create-lockfiles
   You can prevent the creation of lock files by setting the variable
@@ -774,14 +774,14 @@ multiple names, Emacs does not prevent two users from editing it
 simultaneously under different names.
 
   A lock file cannot be written in some circumstances, e.g., if Emacs
-lacks the system permissions or the system does not support symbolic
-links.  In these cases, Emacs can still detect the collision when you
-try to save a file, by checking the file's last-modification date.  If
-the file has changed since the last time Emacs visited or saved it,
-that implies that changes have been made in some other way, and will
-be lost if Emacs proceeds with saving.  Emacs then displays a warning
-message and asks for confirmation before saving; answer @kbd{yes} to
-save, and @kbd{no} or @kbd{C-g} cancel the save.
+lacks the system permissions or cannot create lock files for some
+other reason.  In these cases, Emacs can still detect the collision
+when you try to save a file, by checking the file's last-modification
+date.  If the file has changed since the last time Emacs visited or
+saved it, that implies that changes have been made in some other way,
+and will be lost if Emacs proceeds with saving.  Emacs then displays a
+warning message and asks for confirmation before saving; answer
+@kbd{yes} to save, and @kbd{no} or @kbd{C-g} cancel the save.
 
   If you are notified that simultaneous editing has already taken
 place, one way to compare the buffer to its file is the @kbd{M-x