• Paul Eggert's avatar
    The lock for FILE is now .#FILE or .#-FILE. · b5029e23
    Paul Eggert authored
    The old approach, which fell back on DIR/.#FILE.0 through
    DIR/.#FILE.9, had race conditions that could not be easily fixed.
    If DIR/.#FILE is a non-symlink file, Emacs now does not create a
    lock file for DIR/FILE; that is, DIR/FILE is no longer partly
    protected by a lock if DIR/.#FILE is a non-symlink file ("partly"
    because the locking mechanism was never reliable in that case).
    This patch fixes this and other bugs discovered by a code
    inspection that was prompted by
    <http://lists.gnu.org/archive/html/emacs-devel/2013-02/msg00531.html>.
    Also, this patch switches to .#-FILE (not .#FILE) on MS-Windows,
    to avoid interoperability problems between the MS-Windows and
    non-MS-Windows implementations.  MS-Windows and non-MS-Windows
    instances of Emacs now ignore each others' locks.
    * etc/NEWS: Document this.
    * src/filelock.c (defined_WINDOWSNT): New constant.
    (MAKE_LOCK_NAME, fill_in_lock_file_name):
    Don't create DIR/.#FILE.0 through DIR/.#FILE.9.  Instead, create
    DIR/.#FILE symlinks on non-MS-Windows hosts, and DIR/.#-FILE
    regular files on MS-Windows hosts.
    (MAKE_LOCK_NAME, unlock_file, Ffile_locked_p):
    Use SAFE_ALLOCA to avoid problems with long file names.
    (MAX_LFINFO): Now a local constant, not a global macro.
    (IS_LOCK_FILE): Remove.
    (lock_file_1): Don't inspect errno if symlink call succeeds;
    that's not portable.
    (lock_file): Document that this function can return if lock
    creation fails.
    
    Fixes: debbugs:13807
    b5029e23
ChangeLog 885 KB