Make the lock a thread local variable (#219)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Bernát Gábor <bgabor8@bloomberg.net>

src/filelock/_api.py

@@ -6,7 +6,7 @@
 import time
 import warnings
 from abc import ABC, abstractmethod
-from threading import Lock
+from threading import local
 from types import TracebackType
 from typing import Any
 
@@ -36,7 +36,7 @@ def __exit__(
         self.lock.release()
 
 
-class BaseFileLock(ABC, contextlib.ContextDecorator):
+class BaseFileLock(ABC, contextlib.ContextDecorator, local):
     """Abstract base class for a file lock object."""
 
     def __init__(
@@ -67,9 +67,6 @@ def __init__(
         # The mode for the lock files
         self._mode: int = mode
 
-        # We use this lock primarily for the lock counter.
-        self._thread_lock: Lock = Lock()
-
         # The lock counter is used for implementing the nested locking mechanism. Whenever the lock is acquired, the
         # counter is increased and the lock is only released, when this value is 0 again.
         self._lock_counter: int = 0
@@ -168,18 +165,16 @@ def acquire(
             poll_interval = poll_intervall
 
         # Increment the number right at the beginning. We can still undo it, if something fails.
-        with self._thread_lock:
-            self._lock_counter += 1
+        self._lock_counter += 1
 
         lock_id = id(self)
         lock_filename = self._lock_file
         start_time = time.perf_counter()
         try:
             while True:
-                with self._thread_lock:
-                    if not self.is_locked:
-                        _LOGGER.debug("Attempting to acquire lock %s on %s", lock_id, lock_filename)
-                        self._acquire()
+                if not self.is_locked:
+                    _LOGGER.debug("Attempting to acquire lock %s on %s", lock_id, lock_filename)
+                    self._acquire()
                 if self.is_locked:
                     _LOGGER.debug("Lock %s acquired on %s", lock_id, lock_filename)
                     break
@@ -194,8 +189,7 @@ def acquire(
                     _LOGGER.debug(msg, lock_id, lock_filename, poll_interval)
                     time.sleep(poll_interval)
         except BaseException:  # Something did go wrong, so decrement the counter.
-            with self._thread_lock:
-                self._lock_counter = max(0, self._lock_counter - 1)
+            self._lock_counter = max(0, self._lock_counter - 1)
             raise
         return AcquireReturnProxy(lock=self)
 
@@ -206,17 +200,16 @@ def release(self, force: bool = False) -> None:
 
         :param force: If true, the lock counter is ignored and the lock is released in every case/
         """
-        with self._thread_lock:
-            if self.is_locked:
-                self._lock_counter -= 1
+        if self.is_locked:
+            self._lock_counter -= 1
 
-                if self._lock_counter == 0 or force:
-                    lock_id, lock_filename = id(self), self._lock_file
+            if self._lock_counter == 0 or force:
+                lock_id, lock_filename = id(self), self._lock_file
 
-                    _LOGGER.debug("Attempting to release lock %s on %s", lock_id, lock_filename)
-                    self._release()
-                    self._lock_counter = 0
-                    _LOGGER.debug("Lock %s released on %s", lock_id, lock_filename)
+                _LOGGER.debug("Attempting to release lock %s on %s", lock_id, lock_filename)
+                self._release()
+                self._lock_counter = 0
+                _LOGGER.debug("Lock %s released on %s", lock_id, lock_filename)
 
     def __enter__(self) -> BaseFileLock:
         """

tests/test_filelock.py

@@ -5,13 +5,15 @@
 import os
 import sys
 import threading
+from concurrent.futures import ThreadPoolExecutor
 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
 from types import TracebackType
 from typing import Callable, Iterator, Tuple, Type, Union
+from uuid import uuid4
 
 import pytest
 from _pytest.logging import LogCaptureFixture
@@ -81,6 +83,10 @@ def tmp_path_ro(tmp_path: Path) -> Iterator[Path]:
 
 @pytest.mark.parametrize("lock_type", [FileLock, SoftFileLock])
 @pytest.mark.skipif(sys.platform == "win32", reason="Windows does not have read only folders")
+@pytest.mark.skipif(
+    sys.platform != "win32" and os.geteuid() == 0,  # noqa: SC200
+    reason="Cannot make a read only file (that the current user: root can't read)",
+)
 def test_ro_folder(lock_type: type[BaseFileLock], tmp_path_ro: Path) -> None:
     lock = lock_type(str(tmp_path_ro / "a"))
     with pytest.raises(PermissionError, match="Permission denied"):
@@ -96,6 +102,10 @@ def tmp_file_ro(tmp_path: Path) -> Iterator[Path]:
 
 
 @pytest.mark.parametrize("lock_type", [FileLock, SoftFileLock])
+@pytest.mark.skipif(
+    sys.platform != "win32" and os.geteuid() == 0,  # noqa: SC200
+    reason="Cannot make a read only file (that the current user: root can't read)",
+)
 def test_ro_file(lock_type: type[BaseFileLock], tmp_file_ro: Path) -> None:
     lock = lock_type(str(tmp_file_ro))
     with pytest.raises(PermissionError, match="Permission denied"):
@@ -509,3 +519,60 @@ def test_soft_errors(tmp_path: Path, mocker: MockerFixture) -> None:
     mocker.patch("os.open", side_effect=OSError(ENOSYS, "mock error"))
     with pytest.raises(OSError, match="mock error"):
         SoftFileLock(tmp_path / "a.lock").acquire()
+
+
+def _check_file_read_write(txt_file: Path) -> None:
+    for _ in range(3):
+        uuid = str(uuid4())
+        txt_file.write_text(uuid)
+        assert txt_file.read_text() == uuid
+
+
+@pytest.mark.parametrize("lock_type", [FileLock, SoftFileLock])
+def test_thrashing_with_thread_pool_passing_lock_to_threads(tmp_path: Path, lock_type: type[BaseFileLock]) -> None:
+    def mess_with_file(lock_: BaseFileLock) -> None:
+        with lock_:
+            _check_file_read_write(txt_file)
+
+    lock_file, txt_file = tmp_path / "test.txt.lock", tmp_path / "test.txt"
+    lock = lock_type(lock_file)
+    results = []
+    with ThreadPoolExecutor() as executor:
+        for _ in range(100):
+            results.append(executor.submit(mess_with_file, lock))
+
+    assert all(r.result() is None for r in results)
+
+
+@pytest.mark.parametrize("lock_type", [FileLock, SoftFileLock])
+def test_thrashing_with_thread_pool_global_lock(tmp_path: Path, lock_type: type[BaseFileLock]) -> None:
+    def mess_with_file() -> None:
+        with lock:
+            _check_file_read_write(txt_file)
+
+    lock_file, txt_file = tmp_path / "test.txt.lock", tmp_path / "test.txt"
+    lock = lock_type(lock_file)
+    results = []
+    with ThreadPoolExecutor() as executor:
+        for _ in range(100):
+            results.append(executor.submit(mess_with_file))
+
+    assert all(r.result() is None for r in results)
+
+
+@pytest.mark.parametrize("lock_type", [FileLock, SoftFileLock])
+def test_thrashing_with_thread_pool_lock_recreated_in_each_thread(
+    tmp_path: Path,
+    lock_type: type[BaseFileLock],
+) -> None:
+    def mess_with_file() -> None:
+        with lock_type(lock_file):
+            _check_file_read_write(txt_file)
+
+    lock_file, txt_file = tmp_path / "test.txt.lock", tmp_path / "test.txt"
+    results = []
+    with ThreadPoolExecutor() as executor:
+        for _ in range(100):
+            results.append(executor.submit(mess_with_file))
+
+    assert all(r.result() is None for r in results)