Retry targeted pickle cache entry removal

Author: shaypal5

src/cachier/cores/pickle.py

@@ -172,19 +172,22 @@ def _clear_all_cache_files(self) -> None:
         path, name = os.path.split(self.cache_fpath)
         for subpath in os.listdir(path):
             if subpath.startswith(f"{name}_"):
-                fpath = os.path.join(path, subpath)
-                # Retry loop to handle Windows mandatory file-locking (WinError 32):
-                # portalocker holds an exclusive lock while a thread is computing,
-                # so os.remove() may fail transiently until the lock is released.
-                for attempt in range(3):  # pragma: no branch
-                    try:
-                        os.remove(fpath)
-                        break
-                    except PermissionError:
-                        if attempt < 2:
-                            time.sleep(0.1 * (attempt + 1))
-                        else:
-                            raise
+                self._remove_cache_file_with_retries(os.path.join(path, subpath))
+
+    @staticmethod
+    def _remove_cache_file_with_retries(fpath: str) -> None:
+        # Retry loop to handle Windows mandatory file-locking (WinError 32):
+        # portalocker holds an exclusive lock while a thread is computing,
+        # so os.remove() may fail transiently until the lock is released.
+        for attempt in range(3):  # pragma: no branch
+            try:
+                os.remove(fpath)
+                break
+            except PermissionError:
+                if attempt < 2:
+                    time.sleep(0.1 * (attempt + 1))
+                else:
+                    raise
 
     def _clear_being_calculated_all_cache_files(self) -> None:
         path, name = os.path.split(self.cache_fpath)
@@ -423,7 +426,7 @@ def clear_cache(self) -> None:
     def clear_cache_entry(self, key: str) -> None:
         if self.separate_files:
             with suppress(FileNotFoundError):
-                os.remove(f"{self.cache_fpath}_{key}")
+                self._remove_cache_file_with_retries(f"{self.cache_fpath}_{key}")
             return
 
         with self.lock:

tests/pickle_tests/test_pickle_core.py

@@ -1445,6 +1445,49 @@ def flaky_remove(path):
     assert not os.path.exists(dummy_file)
 
 
+@pytest.mark.pickle
+def test_clear_cache_entry_retries_on_permission_error(tmp_path):
+    """Test clear_cache_entry retries on PermissionError then succeeds."""
+    core = _PickleCore(
+        hash_func=None,
+        cache_dir=tmp_path,
+        pickle_reload=False,
+        wait_for_calc_timeout=10,
+        separate_files=True,
+    )
+
+    def mock_func():
+        pass
+
+    core.set_func(mock_func)
+
+    cache_fpath = core.cache_fpath
+    dummy_file = cache_fpath + "_dummykey"
+    with open(dummy_file, "wb") as f:
+        f.write(b"")
+
+    real_remove = os.remove
+    call_count = 0
+
+    def flaky_remove(path):
+        nonlocal call_count
+        call_count += 1
+        if call_count < 3:
+            raise PermissionError("locked")
+        real_remove(path)
+
+    with (
+        patch("cachier.cores.pickle.os.remove", side_effect=flaky_remove),
+        patch("cachier.cores.pickle.time.sleep") as mock_sleep,
+    ):
+        core.clear_cache_entry("dummykey")
+        assert mock_sleep.call_count == 2
+        mock_sleep.assert_any_call(0.1)
+        mock_sleep.assert_any_call(0.2)
+
+    assert not os.path.exists(dummy_file)
+
+
 @pytest.mark.pickle
 def test_clear_all_cache_files_raises_on_persistent_permission_error(tmp_path):
     """Test _clear_all_cache_files re-raises PermissionError after all retries."""