add file locking for simplest cases protection

1 files changed, 4 insertions, 1 deletions

diff --git a/scripts/xattr_user_id b/scripts/xattr_user_id
index 28a1d99..7badd9d 100755
--- a/scripts/xattr_user_id
+++ b/scripts/xattr_user_id
@@ -46,9 +46,9 @@ Options:
 
 ### standard modules
 import contextlib
+import fcntl
 import functools
 import itertools
-import operator
 import os
 import sys
 
@@ -86,6 +86,9 @@ def main():
     last_used_id = 0
     if args['--state']:
         with contextlib.suppress(FileNotFoundError):
+            lock_fd = open(args['--state'], 'r') # locked until program exits
+            # limitation: if file does not exists yet, file won't be locked
+            fcntl.flock(lock_fd, fcntl.LOCK_EX)
             with open(args['--state'], encoding='utf8') as stream:
                 last_used_id = int(stream.read())