Fix: Global flock fallbacks (#1834)

Use correct fallbacks for global flock file.

- Prevents crash if `XDG_RUNTIME_DIR` is not set.
- Default to `~/.cache` instead of `~/cache`.

Fix #1834

Thank you to Timothy Southwick (@NickNackGus) for this contribution.

---------

Co-authored-by: buhtz <c.buhtz@posteo.jp>

CHANGES

@@ -4,6 +4,7 @@ Version 1.5.3-dev (development of upcoming release)
 * Breaking Change: Minimal Python version 3.9 required (#1731)
 * Fix: Prevent duplicates in Exclude/Include list of Manage Profiles dialog
 * Fix: Fix Qt segmentation fault when canceling out of unconfigured BiT (#1095) (Derek Veit @DerekVeit)
+* Fix: Correct global flock fallbacks (#1834) (Timothy Southwick @NickNackGus)
 * Refactor: Remove class OrderedSet
 
 Version 1.5.2 (2024-08-06)

common/flock.py

@@ -73,7 +73,7 @@ def __init__(self,
 
         # Workaround for #1751. Remove after refactoring Snapshots.backup()
         if disable:
-            return
+            return None
 
         folder = Path(Path.cwd().root) / 'run' / 'lock'
 
@@ -84,23 +84,26 @@ def __init__(self,
         self._file_path = folder / filename
 
         if self._can_use_file(self._file_path):
-            return
+            return None
 
         # Try user specific file lock
         # e.g. /run/user/<UID>
-        self._file_path = Path(os.environ['XDG_RUNTIME_DIR']) / filename
+        self._file_path = Path(
+            os.environ.get('XDG_RUNTIME_DIR',
+                           f'/run/user/{os.getuid()}')
+        ) / filename
 
         if self._can_use_file(self._file_path):
-            return
+            return None
 
         # At last, try users cache dir.
         self._file_path = Path(
             os.environ.get('XDG_CACHE_HOME',
-                           Path.home() / 'cache')
+                           Path.home() / '.cache')
         ) / filename
 
         if self._can_use_file(self._file_path):
-            return
+            return None
 
         raise RuntimeError(
             f'Can not establish global flock file {self._file_path}')
@@ -146,7 +149,7 @@ def __enter__(self):
         # Workaround for #1751. Remove after refactoring Snapshots.backup()
         # See __init__() for details
         if self._file_path is None:
-            return
+            return None
 
         self._log('Set')
 
@@ -162,7 +165,7 @@ def __exit__(self, exc_type, exc_value, exc_tb):
         # Workaround for #1751. Remove after refactoring Snapshots.backup()
         # See __init__() for details
         if self._flock_handle is None:
-            return
+            return None
 
         self._log('Release')
         fcntl.fcntl(self._flock_handle, fcntl.LOCK_UN)