core: fix race condition for file backend

src/cachew/backend/file.py

@@ -35,11 +35,13 @@ def __enter__(self) -> 'FileBackend':
 
     def __exit__(self, *args) -> None:
         if self.jsonl_tmp_fw is not None:
-            self.jsonl_tmp_fw.close()
-
             # might still exist in case of early exit
             self.jsonl_tmp.unlink(missing_ok=True)
 
+            # NOTE: need to unlink first
+            # otherwise possible that someone else might open the file before we unlink it
+            self.jsonl_tmp_fw.close()
+
         if self.jsonl_fr is not None:
             self.jsonl_fr.close()
 

src/cachew/tests/test_cachew.py

@@ -1296,7 +1296,7 @@ def fun():
 
 print("FINISHED")
     '''
-    r = run(['python3', '-c', prog], cwd=tmp_path, stderr=PIPE, stdout=PIPE, check=True)
+    r = run([sys.executable, '-c', prog], cwd=tmp_path, stderr=PIPE, stdout=PIPE, check=True)
     assert r.stdout.strip() == b'FINISHED'
     assert b'Traceback' not in r.stderr