asyncio support (#332)

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

pyproject.toml

@@ -50,6 +50,7 @@ optional-dependencies.testing = [
   "coverage>=7.3.2",
   "diff-cover>=8.0.1",
   "pytest>=7.4.3",
+  "pytest-asyncio>=0.21",
   "pytest-cov>=4.1",
   "pytest-mock>=3.12",
   "pytest-timeout>=2.2",

src/filelock/__init__.py

@@ -17,6 +17,13 @@
 from ._soft import SoftFileLock
 from ._unix import UnixFileLock, has_fcntl
 from ._windows import WindowsFileLock
+from .asyncio import (
+    AsyncAcquireReturnProxy,
+    AsyncSoftFileLock,
+    AsyncUnixFileLock,
+    AsyncWindowsFileLock,
+    BaseAsyncFileLock,
+)
 from .version import version
 
 #: version of the project as a string
@@ -25,23 +32,34 @@
 
 if sys.platform == "win32":  # pragma: win32 cover
     _FileLock: type[BaseFileLock] = WindowsFileLock
+    _AsyncFileLock: type[BaseAsyncFileLock] = AsyncWindowsFileLock
 else:  # pragma: win32 no cover # noqa: PLR5501
     if has_fcntl:
         _FileLock: type[BaseFileLock] = UnixFileLock
+        _AsyncFileLock: type[BaseAsyncFileLock] = AsyncUnixFileLock
     else:
         _FileLock = SoftFileLock
+        _AsyncFileLock = AsyncSoftFileLock
         if warnings is not None:
             warnings.warn("only soft file lock is available", stacklevel=2)
 
 if TYPE_CHECKING:
     FileLock = SoftFileLock
+    AsyncFileLock = AsyncSoftFileLock
 else:
     #: Alias for the lock, which should be used for the current platform.
     FileLock = _FileLock
+    AsyncFileLock = _AsyncFileLock
 
 
 __all__ = [
     "AcquireReturnProxy",
+    "AsyncAcquireReturnProxy",
+    "AsyncFileLock",
+    "AsyncSoftFileLock",
+    "AsyncUnixFileLock",
+    "AsyncWindowsFileLock",
+    "BaseAsyncFileLock",
     "BaseFileLock",
     "FileLock",
     "SoftFileLock",

src/filelock/_api.py

@@ -91,7 +91,7 @@ def __new__(  # noqa: PLR0913
         *,
         blocking: bool = True,  # noqa: ARG003
         is_singleton: bool = False,
-        **kwargs: dict[str, Any],  # capture remaining kwargs for subclasses  # noqa: ARG003
+        **kwargs: Any,  # capture remaining kwargs for subclasses  # noqa: ARG003, ANN401
     ) -> Self:
         """Create a new lock object or if specified return the singleton instance for the lock file."""
         if not is_singleton:

src/filelock/asyncio.py

@@ -0,0 +1,314 @@
+"""An asyncio-based implementation of the file lock."""
+
+from __future__ import annotations
+
+import asyncio
+import contextlib
+import logging
+import os
+import time
+from dataclasses import dataclass
+from threading import local
+from typing import TYPE_CHECKING, Any, Callable, NoReturn
+
+from ._api import BaseFileLock, FileLockContext
+from ._error import Timeout
+from ._soft import SoftFileLock
+from ._unix import UnixFileLock
+from ._windows import WindowsFileLock
+
+if TYPE_CHECKING:
+    import sys
+    from concurrent import futures
+    from types import TracebackType
+
+    if sys.version_info >= (3, 11):  # pragma: no cover (py311+)
+        from typing import Self
+    else:  # pragma: no cover (<py311)
+        from typing_extensions import Self
+
+
+_LOGGER = logging.getLogger("filelock")
+
+
+@dataclass
+class AsyncFileLockContext(FileLockContext):
+    """A dataclass which holds the context for a ``BaseAsyncFileLock`` object."""
+
+    #: Whether run in executor
+    run_in_executor: bool = True
+
+    #: The executor
+    executor: futures.Executor | None = None
+
+    #: The loop
+    loop: asyncio.AbstractEventLoop | None = None
+
+
+class AsyncThreadLocalFileContext(AsyncFileLockContext, local):
+    """A thread local version of the ``FileLockContext`` class."""
+
+
+class AsyncAcquireReturnProxy:
+    """A context-aware object that will release the lock file when exiting."""
+
+    def __init__(self, lock: BaseAsyncFileLock) -> None:  # noqa: D107
+        self.lock = lock
+
+    async def __aenter__(self) -> BaseAsyncFileLock:  # noqa: D105
+        return self.lock
+
+    async def __aexit__(  # noqa: D105
+        self,
+        exc_type: type[BaseException] | None,
+        exc_value: BaseException | None,
+        traceback: TracebackType | None,
+    ) -> None:
+        await self.lock.release()
+
+
+class BaseAsyncFileLock(BaseFileLock):
+    """Base class for asynchronous file locks."""
+
+    def __init__(  # noqa: PLR0913
+        self,
+        lock_file: str | os.PathLike[str],
+        timeout: float = -1,
+        mode: int = 0o644,
+        thread_local: bool = False,  # noqa: FBT001, FBT002
+        *,
+        blocking: bool = True,
+        is_singleton: bool = False,
+        loop: asyncio.AbstractEventLoop | None = None,
+        run_in_executor: bool = True,
+        executor: futures.Executor | None = None,
+    ) -> None:
+        """
+        Create a new lock object.
+
+        :param lock_file: path to the file
+        :param timeout: default timeout when acquiring the lock, in seconds. It will be used as fallback value in \
+            the acquire method, if no timeout value (``None``) is given. If you want to disable the timeout, set it \
+            to a negative value. A timeout of 0 means that there is exactly one attempt to acquire the file lock.
+        :param mode: file permissions for the lockfile
+        :param thread_local: Whether this object's internal context should be thread local or not. If this is set to \
+            ``False`` then the lock will be reentrant across threads.
+        :param blocking: whether the lock should be blocking or not
+        :param is_singleton: If this is set to ``True`` then only one instance of this class will be created \
+            per lock file. This is useful if you want to use the lock object for reentrant locking without needing \
+            to pass the same object around.
+        :param loop: The event loop to use. If not specified, the running event loop will be used.
+        :param run_in_executor: If this is set to ``True`` then the lock will be acquired in an executor.
+        :param executor: The executor to use. If not specified, the default executor will be used.
+
+        """
+        self._is_thread_local = thread_local
+        self._is_singleton = is_singleton
+        if thread_local and run_in_executor:
+            msg = "run_in_executor is not supported when thread_local is True"
+            raise ValueError(msg)
+
+        # Create the context. Note that external code should not work with the context directly and should instead use
+        # properties of this class.
+        kwargs: dict[str, Any] = {
+            "lock_file": os.fspath(lock_file),
+            "timeout": timeout,
+            "mode": mode,
+            "blocking": blocking,
+            "loop": loop,
+            "run_in_executor": run_in_executor,
+            "executor": executor,
+        }
+        self._context: AsyncFileLockContext = (AsyncThreadLocalFileContext if thread_local else AsyncFileLockContext)(
+            **kwargs
+        )
+
+    @property
+    def run_in_executor(self) -> bool:
+        """::return: whether run in executor."""
+        return self._context.run_in_executor
+
+    @property
+    def executor(self) -> futures.Executor | None:
+        """::return: the executor."""
+        return self._context.executor
+
+    @executor.setter
+    def executor(self, value: futures.Executor | None) -> None:  # pragma: no cover
+        """
+        Change the executor.
+
+        :param value: the new executor or ``None``
+        :type value: futures.Executor | None
+
+        """
+        self._context.executor = value
+
+    @property
+    def loop(self) -> asyncio.AbstractEventLoop | None:
+        """::return: the event loop."""
+        return self._context.loop
+
+    async def acquire(  # type: ignore[override]
+        self,
+        timeout: float | None = None,
+        poll_interval: float = 0.05,
+        *,
+        blocking: bool | None = None,
+    ) -> AsyncAcquireReturnProxy:
+        """
+        Try to acquire the file lock.
+
+        :param timeout: maximum wait time for acquiring the lock, ``None`` means use the default
+            :attr:`~BaseFileLock.timeout` is and if ``timeout < 0``, there is no timeout and
+            this method will block until the lock could be acquired
+        :param poll_interval: interval of trying to acquire the lock file
+        :param blocking: defaults to True. If False, function will return immediately if it cannot obtain a lock on the
+         first attempt. Otherwise, this method will block until the timeout expires or the lock is acquired.
+        :raises Timeout: if fails to acquire lock within the timeout period
+        :return: a context object that will unlock the file when the context is exited
+
+        .. code-block:: python
+
+            # You can use this method in the context manager (recommended)
+            with lock.acquire():
+                pass
+
+            # Or use an equivalent try-finally construct:
+            lock.acquire()
+            try:
+                pass
+            finally:
+                lock.release()
+
+        """
+        # Use the default timeout, if no timeout is provided.
+        if timeout is None:
+            timeout = self._context.timeout
+
+        if blocking is None:
+            blocking = self._context.blocking
+
+        # Increment the number right at the beginning. We can still undo it, if something fails.
+        self._context.lock_counter += 1
+
+        lock_id = id(self)
+        lock_filename = self.lock_file
+        start_time = time.perf_counter()
+        try:
+            while True:
+                if not self.is_locked:
+                    _LOGGER.debug("Attempting to acquire lock %s on %s", lock_id, lock_filename)
+                    await self._run_internal_method(self._acquire)
+                if self.is_locked:
+                    _LOGGER.debug("Lock %s acquired on %s", lock_id, lock_filename)
+                    break
+                if blocking is False:
+                    _LOGGER.debug("Failed to immediately acquire lock %s on %s", lock_id, lock_filename)
+                    raise Timeout(lock_filename)  # noqa: TRY301
+                if 0 <= timeout < time.perf_counter() - start_time:
+                    _LOGGER.debug("Timeout on acquiring lock %s on %s", lock_id, lock_filename)
+                    raise Timeout(lock_filename)  # noqa: TRY301
+                msg = "Lock %s not acquired on %s, waiting %s seconds ..."
+                _LOGGER.debug(msg, lock_id, lock_filename, poll_interval)
+                await asyncio.sleep(poll_interval)
+        except BaseException:  # Something did go wrong, so decrement the counter.
+            self._context.lock_counter = max(0, self._context.lock_counter - 1)
+            raise
+        return AsyncAcquireReturnProxy(lock=self)
+
+    async def release(self, force: bool = False) -> None:  # type: ignore[override]  # noqa: FBT001, FBT002
+        """
+        Releases the file lock. Please note, that the lock is only completely released, if the lock counter is 0.
+        Also note, that the lock file itself is not automatically deleted.
+
+        :param force: If true, the lock counter is ignored and the lock is released in every case/
+
+        """
+        if self.is_locked:
+            self._context.lock_counter -= 1
+
+            if self._context.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)
+                await self._run_internal_method(self._release)
+                self._context.lock_counter = 0
+                _LOGGER.debug("Lock %s released on %s", lock_id, lock_filename)
+
+    async def _run_internal_method(self, method: Callable[[], Any]) -> None:
+        if asyncio.iscoroutinefunction(method):
+            await method()
+        elif self.run_in_executor:
+            loop = self.loop or asyncio.get_running_loop()
+            await loop.run_in_executor(self.executor, method)
+        else:
+            method()
+
+    def __enter__(self) -> NoReturn:
+        """
+        Replace old __enter__ method to avoid using it.
+
+        NOTE: DO NOT USE `with` FOR ASYNCIO LOCKS, USE `async with` INSTEAD.
+
+        :return: none
+        :rtype: NoReturn
+        """
+        msg = "Do not use `with` for asyncio locks, use `async with` instead."
+        raise NotImplementedError(msg)
+
+    async def __aenter__(self) -> Self:
+        """
+        Acquire the lock.
+
+        :return: the lock object
+
+        """
+        await self.acquire()
+        return self
+
+    async def __aexit__(
+        self,
+        exc_type: type[BaseException] | None,
+        exc_value: BaseException | None,
+        traceback: TracebackType | None,
+    ) -> None:
+        """
+        Release the lock.
+
+        :param exc_type: the exception type if raised
+        :param exc_value: the exception value if raised
+        :param traceback: the exception traceback if raised
+
+        """
+        await self.release()
+
+    def __del__(self) -> None:
+        """Called when the lock object is deleted."""
+        with contextlib.suppress(RuntimeError):
+            loop = self.loop or asyncio.get_running_loop()
+            if not loop.is_running():  # pragma: no cover
+                loop.run_until_complete(self.release(force=True))
+            else:
+                loop.create_task(self.release(force=True))
+
+
+class AsyncSoftFileLock(SoftFileLock, BaseAsyncFileLock):
+    """Simply watches the existence of the lock file."""
+
+
+class AsyncUnixFileLock(UnixFileLock, BaseAsyncFileLock):
+    """Uses the :func:`fcntl.flock` to hard lock the lock file on unix systems."""
+
+
+class AsyncWindowsFileLock(WindowsFileLock, BaseAsyncFileLock):
+    """Uses the :func:`msvcrt.locking` to hard lock the lock file on windows systems."""
+
+
+__all__ = [
+    "AsyncAcquireReturnProxy",
+    "AsyncSoftFileLock",
+    "AsyncUnixFileLock",
+    "AsyncWindowsFileLock",
+    "BaseAsyncFileLock",
+]