Fix trying to infinitely acquire a lock if flock is not implemented

.pre-commit-config.yaml

@@ -44,6 +44,10 @@ repos:
     hooks:
       - id: tox-ini-fmt
         args: ["-p", "fix"]
+  - repo: https://github.com/tox-dev/pyproject-fmt
+    rev: "0.9.2"
+    hooks:
+      - id: pyproject-fmt
   - repo: https://github.com/PyCQA/flake8
     rev: 6.0.0
     hooks:

docs/changelog.rst

@@ -1,5 +1,9 @@
 Changelog
 =========
+v3.10.5 (2023-03-25)
+--------------------
+- Add explicit error check as certain UNIX filesystems do not support flock. by :user:`jahrules`.
+
 v3.10.4 (2023-03-24)
 --------------------
 - Update os.open to preserve mode= for certain edge cases. by :user:`jahrules`.

pyproject.toml

@@ -42,8 +42,10 @@ optional-dependencies.docs = [
 optional-dependencies.testing = [
   "covdefaults>=2.3",
   "coverage>=7.2.2",
+  "diff-cover>=7.5",
   "pytest>=7.2.2",
   "pytest-cov>=4",
+  "pytest-mock>=3.10",
   "pytest-timeout>=2.1",
 ]
 urls.Documentation = "https://py-filelock.readthedocs.io"
@@ -56,6 +58,21 @@ build.hooks.vcs.version-file = "src/filelock/version.py"
 build.targets.sdist.include = ["/src", "/tests"]
 version.source = "vcs"
 
+[tool.black]
+line-length = 120
+
+[tool.isort]
+profile = "black"
+known_first_party = ["filelock"]
+add_imports = ["from __future__ import annotations"]
+
+[tool.flake8]
+max-complexity = 22
+max-line-length = 120
+unused-arguments-ignore-abstract-functions = true
+noqa-require-code = true
+dictionaries = ["en_US", "python", "technical", "django"]
+
 [tool.coverage]
 html.show_contexts = true
 html.skip_covered = false
@@ -65,14 +82,6 @@ report.fail_under = 76
 run.parallel = true
 run.plugins = ["covdefaults"]
 
-[tool.black]
-line-length = 120
-
-[tool.isort]
-profile = "black"
-known_first_party = ["filelock"]
-add_imports = ["from __future__ import annotations"]
-
 [tool.mypy]
 python_version = "3.11"
 show_error_codes = true
@@ -81,10 +90,3 @@ overrides = [{ module = ["appdirs.*", "jnius.*"], ignore_missing_imports = true
 
 [tool.pep8]
 max-line-length = "120"
-
-[tool.flake8]
-max-complexity = 22
-max-line-length = 120
-unused-arguments-ignore-abstract-functions = true
-noqa-require-code = true
-dictionaries = ["en_US", "python", "technical", "django"]

src/filelock/_unix.py

@@ -2,6 +2,7 @@
 
 import os
 import sys
+from errno import ENOSYS
 from typing import cast
 
 from ._api import BaseFileLock
@@ -39,8 +40,10 @@ def _acquire(self) -> None:
                 pass  # This locked is not owned by this UID
             try:
                 fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
-            except OSError:
+            except OSError as exception:
                 os.close(fd)
+                if exception.errno == ENOSYS:  # NotImplemented error
+                    raise NotImplementedError("FileSystem does not appear to support flock; user SoftFileLock instead")
             else:
                 self._lock_file_fd = fd
 

tests/test_filelock.py

@@ -6,6 +6,7 @@
 import sys
 import threading
 from contextlib import contextmanager
+from errno import ENOSYS
 from inspect import getframeinfo, stack
 from pathlib import Path, PurePath
 from stat import S_IWGRP, S_IWOTH, S_IWUSR, filemode
@@ -14,6 +15,7 @@
 
 import pytest
 from _pytest.logging import LogCaptureFixture
+from pytest_mock import MockerFixture
 
 from filelock import (
     BaseFileLock,
@@ -494,3 +496,11 @@ def test_wrong_platform(tmp_path: Path) -> None:
         lock.acquire()
     with pytest.raises(NotImplementedError):
         lock._release()
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="flock not run on windows")
+def test_flock_not_implemented_unix(tmp_path: Path, mocker: MockerFixture) -> None:
+    mocker.patch("fcntl.flock", side_effect=OSError(ENOSYS, "mock error"))
+    with pytest.raises(NotImplementedError):
+        with FileLock(str(tmp_path / "a.lock")):
+            pass

tox.ini

@@ -29,6 +29,7 @@ commands =
       --cov-config=pyproject.toml --no-cov-on-fail --cov-report term-missing:skip-covered --cov-context=test \
       --cov-report html:{envtmpdir}{/}htmlcov --cov-report xml:{toxworkdir}{/}coverage.{envname}.xml \
       tests}
+    diff-cover --compare-branch {env:DIFF_AGAINST:origin/main} {toxworkdir}{/}coverage.{envname}.xml
 package = wheel
 wheel_build_env = .pkg
 

whitelist.txt

@@ -3,6 +3,7 @@ autodoc
 autosectionlabel
 caplog
 eacces
+enosys
 extlinks
 filelock
 filemode