set sticky bit on connection files

avoids periodic cleanup of runtime directory

jupyter_client/connect.py

@@ -14,6 +14,7 @@
 import json
 import os
 import socket
+import stat
 import tempfile
 import warnings
 from getpass import getpass
@@ -135,6 +136,21 @@ def write_connection_file(fname=None, shell_port=0, iopub_port=0, stdin_port=0,
     with open(fname, 'w') as f:
         f.write(json.dumps(cfg, indent=2))
 
+    if hasattr(stat, 'S_ISVTX'):
+        # set the sticky bit to avoid periodic cleanup
+        permissions = os.stat(fname).st_mode
+        new_permissions = permissions | stat.S_ISVTX
+        if new_permissions != permissions:
+            try:
+                os.chmod(fname, permissions)
+            except OSError as e:
+                # failed to set sticky bit,
+                # probably not a big deal
+                warnings.warn(
+                    "Failed to set sticky bit on %r: %s" % (fname, e),
+                    RuntimeWarning,
+                )
+
     return fname, cfg