"""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 inspect import iscoroutinefunction from threading import local from typing import TYPE_CHECKING, Final, NoReturn, TypeVar, cast from ._api import ( _UNSET_FILE_MODE, BaseFileLock, CloseErrorPolicy, ContextErrorPolicy, FileLockContext, FileLockMeta, _append_exception_context, _canonical, _ExtraValue, _fork_transition, _grouped_errors, _raise_body_and_release, _raise_chained_errors, _raise_cleanup_errors, _raise_grouped_errors, _register_fork_object, ) from ._async import ( _AsyncTransitionGate, _AsyncTransitionUnavailableError, _BackendOutcome, _capture_awaitable, _capture_call, _drain_future, _future_result, _wait_until_done, ) from ._error import Timeout from ._lease import SoftFileLease from ._soft import SoftFileLock from ._strict import StrictSoftFileLock from ._unix import UnixFileLock from ._windows import WindowsFileLock if TYPE_CHECKING: import sys from collections.abc import Awaitable, Callable, Coroutine, Hashable 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 ( _AT: if thread_local and run_in_executor: msg = "run_in_executor is not supported when thread_local is True" raise ValueError(msg) return super().__call__( # a subclass may add options of its own, as AsyncSoftFileLease does **kwargs, lock_file=lock_file, timeout=timeout, mode=mode, thread_local=thread_local, blocking=blocking, is_singleton=is_singleton, poll_interval=poll_interval, lifetime=lifetime, context_error_policy=context_error_policy, close_error_policy=close_error_policy, fallback_to_soft=fallback_to_soft, preserve_lock_file=preserve_lock_file, on_acquired=on_acquired, loop=loop, run_in_executor=run_in_executor, executor=executor, ) class BaseAsyncFileLock(BaseFileLock, metaclass=AsyncFileLockMeta): """ Base class for asynchronous file locks. .. versionadded:: 3.15.0 """ _deadlock_holder_desc: str = "BaseAsyncFileLock instance in this task" _constructor_lifetime_warning_stacklevel: int = 4 @staticmethod def _deadlock_scope() -> Hashable | None: # One event loop thread runs every task, so a thread-scoped registry cannot tell a same-task reacquire # (a real deadlock: the polling task never reaches its own release) from another task queuing behind the # holder (no deadlock: each poll yields, so the holder runs on and releases). Only the first may fail # fast, so scope holders to the task. return asyncio.current_task() def __init__( # ruff:ignore[too-many-arguments] # public constructor: one parameter per documented lock option self, lock_file: str | os.PathLike[str], timeout: float = -1, mode: int = _UNSET_FILE_MODE, thread_local: bool = False, # ruff:ignore[boolean-type-hint-positional-argument, boolean-default-value-positional-argument] # public API: positional bool kept for backwards compatibility *, blocking: bool = True, is_singleton: bool = False, poll_interval: float = 0.05, lifetime: float | None = None, context_error_policy: ContextErrorPolicy = "chain", close_error_policy: CloseErrorPolicy = "default", fallback_to_soft: bool = True, preserve_lock_file: bool = False, on_acquired: Callable[[int], None] | None = None, 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. When not specified, the OS controls permissions via umask and default ACLs, preserving POSIX default ACL inheritance in shared directories. :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. When ``True`` (the default), **all fields of the lock's internal context are per-thread**, including the configuration values ``poll_interval``, ``timeout``, ``blocking``, ``mode``, and ``lifetime``. Setting one of these properties from one thread does not change the value seen by another thread; threads that did not perform the write continue to see the value supplied at construction time. If you need configuration values to be visible across threads, construct the lock with ``thread_local=False``. :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 poll_interval: default interval for polling the lock file, in seconds. It will be used as fallback value in the acquire method, if no poll_interval value (``None``) is given. :param lifetime: for :class:`AsyncSoftFileLock`, the age in seconds after which a waiting process may delete the marker, even while its holder remains alive. This legacy expiry mode does not provide strict mutual exclusion. ``None`` (the default) disables age-based expiry. Native OS locks (:class:`AsyncFileLock`) cannot be revoked by file age and ignore a non-``None`` ``lifetime`` with a warning. :param context_error_policy: how a context manager reconciles a failure in its body with a failure while releasing on exit. ``"chain"`` (the default) keeps Python's behavior: the release error propagates with the body error in its ``__context__``. ``"group"`` raises a :class:`BaseExceptionGroup` holding the body error first and the release error second, so neither hides the other. :param close_error_policy: for native locks (:class:`AsyncFileLock`), what to do with an ``os.close`` failure after the OS unlock has already committed. ``"default"`` keeps each platform's historical behavior, ``"raise"`` always propagates the ``OSError``, and ``"suppress"`` always ignores it. :param fallback_to_soft: for :class:`AsyncFileLock`, whether to fall back to soft existence locking when ``flock`` returns ``ENOSYS``. ``True`` (default) keeps the fallback; ``False`` propagates the error. :param preserve_lock_file: for native locks (:class:`AsyncFileLock`), whether filelock promises not to unlink the lock pathname on release. ``False`` (default) keeps each backend's cleanup; ``True`` keeps a stable file identity (Windows skips its unlink, Unix refuses the ``ENOSYS`` soft fallback). :class:`AsyncSoftFileLock` rejects ``True``. :param on_acquired: for native locks (:class:`AsyncFileLock`), a callable invoked with the borrowed lock descriptor once per physical acquisition, after the lock is held but before :meth:`~BaseAsyncFileLock.acquire` returns. With ``run_in_executor=True`` (the default) it runs in the backend executor. It must not close or unlock the descriptor; a raise rolls the acquisition back. :class:`AsyncSoftFileLock` rejects it. :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._creator_pid = os.getpid() self._is_thread_local = thread_local self._is_singleton = is_singleton self._context_error_policy = context_error_policy # already validated by the metaclass self._close_error_policy = close_error_policy # already validated by the metaclass self._fallback_to_soft = fallback_to_soft self._preserve_lock_file = preserve_lock_file # already validated by the metaclass self._on_acquired = on_acquired # already validated by the metaclass self._transition_gate: Final[_AsyncTransitionGate] = _AsyncTransitionGate() self._context: AsyncFileLockContext = (AsyncThreadLocalFileContext if thread_local else AsyncFileLockContext)( lock_file=os.fspath(lock_file), timeout=timeout, mode=mode, blocking=blocking, poll_interval=poll_interval, lifetime=lifetime, loop=loop, run_in_executor=run_in_executor, executor=executor, ) _register_fork_object(self) @property def run_in_executor(self) -> bool: """Whether run in executor.""" return self._context.run_in_executor @property def executor(self) -> futures.Executor | None: """The executor.""" return self._context.executor @executor.setter def executor(self, value: futures.Executor | None) -> None: # pragma: no cover """ Change the executor. :param futures.Executor | None value: the new executor or ``None`` """ self._context.executor = value @property def loop(self) -> asyncio.AbstractEventLoop | None: """The event loop.""" return self._context.loop async def acquire( # ty: ignore[invalid-method-override] self, timeout: float | None = None, poll_interval: float | None = None, *, blocking: bool | None = None, cancel_check: Callable[[], 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, ``None`` means use the default :attr:`~BaseFileLock.poll_interval` :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. :param cancel_check: a callable returning ``True`` when the acquisition should be canceled. Checked on each poll iteration. When triggered, raises :class:`~Timeout` just like an expired timeout. :returns: a context object that will unlock the file when the context is exited :raises Timeout: if fails to acquire lock within the timeout period .. 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() """ self._raise_if_inherited() if timeout is None: timeout = self._context.timeout if blocking is None: blocking = self._context.blocking if poll_interval is None: poll_interval = self._context.poll_interval start_time = time.perf_counter() try: return await self._acquire_with_admission( blocking=blocking, cancel_check=cancel_check, timeout=timeout, poll_interval=poll_interval, start_time=start_time, ) except _AsyncTransitionUnavailableError: raise Timeout(self.lock_file) from None async def _acquire_with_admission( self, *, blocking: bool, cancel_check: Callable[[], bool] | None, timeout: float, poll_interval: float, start_time: float, ) -> AsyncAcquireReturnProxy: async with self._transition_gate.hold_for_acquire( blocking=blocking, cancel_check=cancel_check, deadline=None if timeout < 0 else start_time + timeout, poll_interval=poll_interval, ): # A canceled provisional acquire must finish rollback before another caller can claim its descriptor. canonical = _canonical(self.lock_file) self._context.lock_counter += 1 self._raise_if_would_deadlock(canonical, timeout=timeout, blocking=blocking) self._context.claim_root = canonical try: await self._async_poll_until_acquired( blocking=blocking, cancel_check=cancel_check, timeout=timeout, poll_interval=poll_interval, start_time=start_time, ) except BaseException: self._reconcile_failed_acquire(canonical) raise finally: self._context.claim_root = None self._commit_acquire(canonical) return AsyncAcquireReturnProxy(lock=self) async def _async_poll_until_acquired( self, *, blocking: bool, cancel_check: Callable[[], bool] | None, timeout: float, poll_interval: float, start_time: float, ) -> None: lock_id = id(self) lock_filename = self.lock_file while True: self._raise_if_inherited() if not self.is_locked: self._try_break_expired_lock() _LOGGER.debug("Attempting to acquire lock %s on %s", lock_id, lock_filename) await self._run_acquire_attempt() self._raise_if_inherited() if self.is_locked: _LOGGER.debug("Lock %s acquired on %s", lock_id, lock_filename) return if self._check_give_up( blocking=blocking, cancel_check=cancel_check, timeout=timeout, start_time=start_time, ): raise Timeout(lock_filename) _LOGGER.debug("Lock %s not acquired on %s, waiting %s seconds ...", lock_id, lock_filename, poll_interval) await asyncio.sleep(poll_interval) async def _run_acquire_attempt(self) -> None: acquire_future = self._start_internal_method( self._acquire_with_fork_tracking_async if iscoroutinefunction(self._acquire) else self._acquire_with_fork_tracking ) try: await _wait_until_done(acquire_future) except asyncio.CancelledError as cancellation: acquire_error: BaseException | None = None try: await _drain_future(acquire_future) except BaseException as error: # ruff:ignore[blind-except] # reported with the cancellation below acquire_error = error rollback_error: BaseException | None = None if self.is_locked: try: await _drain_future(self._start_tracked_release()) except BaseException as error: # ruff:ignore[blind-except] # reported with the cancellation below rollback_error = error if acquire_error is not None: if rollback_error is not None: # pragma: needs fcntl self._raise_cancelled_errors( "lock acquisition cancellation, backend attempt, and rollback failed", cancellation, acquire_error, rollback_error, ) self._raise_cancelled_errors( "lock acquisition cancellation and backend attempt both failed", cancellation, acquire_error ) if rollback_error is not None: self._raise_cancelled_errors( "lock acquisition cancellation and rollback both failed", cancellation, rollback_error ) raise try: _future_result(acquire_future) except asyncio.CancelledError as acquire_error: await self._rollback_backend_cancelled_acquire(acquire_error) async def _rollback_backend_cancelled_acquire(self, acquire_error: asyncio.CancelledError) -> NoReturn: if self.is_locked: try: await _drain_future(self._start_tracked_release()) except BaseException as rollback_error: # ruff:ignore[blind-except] # both backend errors must surface self._raise_acquire_rollback_errors(acquire_error, rollback_error) raise acquire_error def _raise_acquire_rollback_errors(self, acquire_error: BaseException, rollback_error: BaseException) -> NoReturn: if self._context_error_policy == "group": _raise_grouped_errors("lock acquisition backend and rollback both failed", acquire_error, rollback_error) _raise_chained_errors(acquire_error, rollback_error) def _raise_cancelled_errors( self, message: str, cancellation: asyncio.CancelledError, first_error: BaseException, second_error: BaseException | None = None, ) -> NoReturn: if self._context_error_policy == "group": marker = ( (_ASYNC_RELEASE_CANCELLATION_MARKER_ATTR, _ASYNC_RELEASE_CANCELLATION_MARKER) if message == _ASYNC_RELEASE_CANCELLATION_ERRORS else None ) if second_error is None: _raise_grouped_errors(message, cancellation, first_error, marker=marker) _raise_grouped_errors(message, cancellation, first_error, second_error, marker=marker) if (context := first_error.__context__) is not None and context is not cancellation: if (cancellation_context := cancellation.__context__) is not None: _append_exception_context(context, cancellation_context) cancellation.__context__ = context first_error.__context__ = cancellation _raise_chained_errors(first_error, second_error) async def release(self, force: bool = False) -> None: # ty: ignore[invalid-method-override] # ruff:ignore[boolean-type-hint-positional-argument, boolean-default-value-positional-argument] # public API: positional bool kept for backwards compatibility """ Release the file lock. The lock is only completely released when the lock counter reaches 0. The lock file itself may be deleted automatically, the behavior is platform-specific. :param force: If true, the lock counter is ignored and the lock is released in every case. """ if self._creator_pid != os.getpid() or not self.is_locked: return async with self._transition_gate.hold(): await self._release_serialized(force=force) async def _release_serialized(self, *, force: bool) -> None: if not self.is_locked: return if not force and self._context.lock_counter > 1: self._context.lock_counter -= 1 return lock_id, lock_filename = id(self), self.lock_file _LOGGER.debug("Attempting to release lock %s on %s", lock_id, lock_filename) release_future = self._start_tracked_release() try: await _wait_until_done(release_future) except asyncio.CancelledError as cancellation: try: await _drain_future(release_future) except BaseException as release_error: # ruff:ignore[blind-except] # cancellation and backend failure must both surface self._commit_release_if_released() self._raise_cancelled_errors(_ASYNC_RELEASE_CANCELLATION_ERRORS, cancellation, release_error) self._commit_release() raise try: _future_result(release_future) except BaseException: # state follows the backend for control-flow exceptions too self._commit_release_if_released() raise self._commit_release() _LOGGER.debug("Lock %s released on %s", lock_id, lock_filename) def _commit_release_if_released(self) -> None: # Commit only when the backend actually unlocked (close or unlink failed after the OS unlock). If the lock is # still held, keep the counter so a later release can retry. if not self.is_locked: self._commit_release() def _start_internal_method( self, method: Callable[[], None] | Callable[[], Coroutine[None, None, None]] ) -> asyncio.Future[_BackendOutcome[None]]: if iscoroutinefunction(method): return asyncio.create_task(_capture_awaitable(cast("Callable[[], Coroutine[None, None, None]]", method)())) loop = asyncio.get_running_loop() sync_method = cast("Callable[[], None]", method) if self.run_in_executor: return loop.run_in_executor(self.executor, _capture_call, sync_method) future: asyncio.Future[_BackendOutcome[None]] = loop.create_future() future.set_result(_capture_call(sync_method)) return future def _start_tracked_release(self) -> asyncio.Future[_BackendOutcome[None]]: return self._start_internal_method( self._release_with_fork_tracking_async if iscoroutinefunction(self._release) else self._release_with_fork_tracking ) async def _acquire_with_fork_tracking_async(self) -> None: with _fork_transition(self): try: await cast("Callable[[], Awaitable[None]]", self._acquire)() except BaseException as acquisition_error: await self._rollback_failed_acquire_async(acquisition_error) raise try: self._register_context_descriptor() except BaseException as registration_error: # cancellation must roll back the descriptor await self._rollback_failed_registration_async(registration_error) raise if self.is_locked: await self._invoke_on_acquired_async() async def _rollback_failed_acquire_async(self, acquisition_error: BaseException) -> None: if not self.is_locked: return registration_error: BaseException | None = None tracking_error: BaseException | None = None try: self._register_context_descriptor() except BaseException as error: # ruff:ignore[blind-except] # preserve registration and acquisition failures registration_error = error try: # Rollback may fail too; retain the fd so a child can close it without another identity probe. self._register_unverified_context_descriptor() except BaseException as error: # ruff:ignore[blind-except] # pragma: no cover - allocation/control-flow during fallback tracking_error = error try: await _drain_future(self._start_tracked_release()) except BaseException as rollback_error: # ruff:ignore[blind-except] # preserve rollback and acquisition failures if registration_error is None and tracking_error is None: self._raise_acquire_rollback_errors(acquisition_error, rollback_error) _raise_cleanup_errors( "lock acquisition cleanup failed", acquisition_error, registration_error, tracking_error, rollback_error, ) if registration_error is not None: _raise_cleanup_errors( "lock acquisition cleanup failed", acquisition_error, registration_error, tracking_error ) async def _rollback_failed_registration_async(self, registration_error: BaseException) -> None: tracking_error: BaseException | None = None try: # Rollback may fail too; retain the fd so a child can close it without another identity probe. self._register_unverified_context_descriptor() except BaseException as error: # ruff:ignore[blind-except] # pragma: no cover - allocation/control-flow during fallback tracking_error = error try: await _drain_future(self._start_tracked_release()) except BaseException as rollback_error: # ruff:ignore[blind-except] # preserve rollback and registration failures _raise_cleanup_errors( "descriptor registration cleanup failed", registration_error, tracking_error, rollback_error ) if tracking_error is not None: # pragma: no cover - requires failed in-memory fallback _raise_cleanup_errors("descriptor registration cleanup failed", registration_error, tracking_error) async def _invoke_on_acquired_async(self) -> None: if self._on_acquired is None or self._context.lock_counter != 1: return try: self._on_acquired(cast("int", self._context.lock_file_fd)) except BaseException as callback_error: # caller control-flow errors must release the lock callback_context = callback_error.__context__ try: await _drain_future(self._start_tracked_release()) except BaseException as release_error: # ruff:ignore[blind-except] # both errors surface via the group below _raise_body_and_release(callback_error, release_error) callback_error.__context__ = callback_context raise async def _release_with_fork_tracking_async(self) -> None: with _fork_transition(self): try: await cast("Callable[[], Awaitable[None]]", self._release)() finally: self._unregister_released_descriptor() def __enter__(self) -> NoReturn: """Sync context manager entry is not supported because lock acquisition is a coroutine.""" msg = "Use `async with`: acquire/release are coroutines and cannot be awaited in a sync context manager." raise NotImplementedError(msg) def __exit__( self, exc_type: type[BaseException] | None, exc_value: BaseException | None, traceback: TracebackType | None, ) -> None: """Sync context manager exit is not supported because lock release is a coroutine.""" msg = "Use `async with`: acquire/release are coroutines and cannot be awaited in a sync context manager." raise NotImplementedError(msg) async def __aenter__(self) -> Self: """ Acquire the lock. :returns: 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, reconciling a release failure with any body failure per :attr:`context_error_policy`. :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_in_context(exc_value) async def _release_in_context( # ty: ignore[invalid-method-override] self, body_error: BaseException | None ) -> None: # The async counterpart of BaseFileLock._release_in_context: await release, then apply the same policy. try: await self.release() except BaseException as release_error: if body_error is None: raise if self._context_error_policy == "chain": _append_exception_context(release_error, body_error) raise if ( errors := _grouped_errors( release_error, _ASYNC_RELEASE_CANCELLATION_ERRORS, (_ASYNC_RELEASE_CANCELLATION_MARKER_ATTR, _ASYNC_RELEASE_CANCELLATION_MARKER), ) ) is not None: match errors: # The marker is only ever set on a (CancelledError, backend_error) pair, so this always matches. case (asyncio.CancelledError() as cancellation, backend_error): # pragma: no branch _raise_grouped_errors(_ASYNC_CONTEXT_RELEASE_ERRORS, body_error, cancellation, backend_error) _raise_body_and_release(body_error, release_error) def __del__(self) -> None: """Release on deletion; safe to call during GC even when no event loop is running.""" if vars(self).get("_creator_pid") != os.getpid(): return # pragma: forked child with contextlib.suppress(Exception): try: loop = asyncio.get_running_loop() except RuntimeError: loop = self._context.loop if self._context.loop and not self._context.loop.is_closed() else None if loop is None: return if not loop.is_running(): # pragma: no cover loop.run_until_complete(self.release(force=True)) else: loop.create_task(self.release(force=True)) @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: # ruff:ignore[undocumented-public-init] # trivial release-on-exit proxy self.lock = lock async def __aenter__(self) -> BaseAsyncFileLock: # ruff:ignore[undocumented-magic-method] # returns the wrapped lock return self.lock async def __aexit__( # ruff:ignore[undocumented-magic-method] # releases the wrapped lock on exit self, exc_type: type[BaseException] | None, exc_value: BaseException | None, traceback: TracebackType | None, ) -> None: await self.lock._release_in_context(exc_value) # ruff:ignore[private-member-access] # releases the wrapped lock's context class AsyncSoftFileLock(SoftFileLock, BaseAsyncFileLock): """Simply watches the existence of the lock file.""" _lifetime_replacements: tuple[str, str] | None = ("AsyncStrictSoftFileLock", "AsyncSoftFileLease") class AsyncStrictSoftFileLock(StrictSoftFileLock, BaseAsyncFileLock): """Run strict owner-claim locking without blocking the event loop.""" class AsyncSoftFileLease(SoftFileLease, BaseAsyncFileLock): """Existence lock whose claim expires, so a peer may take it while the previous holder still runs.""" 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", "AsyncSoftFileLease", "AsyncSoftFileLock", "AsyncStrictSoftFileLock", "AsyncUnixFileLock", "AsyncWindowsFileLock", "BaseAsyncFileLock", ]