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8ddc930 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 | """Async wrapper around :class:`ReadWriteLock` for use with ``asyncio``."""
from __future__ import annotations
import asyncio
import functools
import os
import sqlite3
from concurrent.futures import ThreadPoolExecutor
from contextlib import asynccontextmanager
from typing import TYPE_CHECKING, ParamSpec, TypeVar
from ._api import (
_append_exception_context,
_ensure_current_process,
_fork_transition,
_register_fork_object,
)
from ._async import (
_BackendOutcome,
_capture_call,
_drain_future,
_future_result,
_raise_cancelled_error,
_wait_until_done,
)
from ._read_write import ReadWriteLock
if TYPE_CHECKING:
from collections.abc import AsyncGenerator, Callable
from concurrent import futures
from types import TracebackType
from ._api import AcquireReturnProxy
_P = ParamSpec("_P")
_R = TypeVar("_R")
class AsyncReadWriteLock:
"""
Async wrapper around :class:`ReadWriteLock` for use in ``asyncio`` applications.
This wrapper dispatches every blocking SQLite operation to a thread pool via ``loop.run_in_executor()`` because
Python's :mod:`sqlite3` module has no async API. It delegates reentrancy, upgrade/downgrade rules, and singleton
behavior to the underlying :class:`ReadWriteLock`.
:param lock_file: path to the SQLite database file used as the lock
:param timeout: maximum wait time in seconds; ``-1`` means block indefinitely
:param blocking: if ``False``, raise :class:`~filelock.Timeout` immediately when the lock is unavailable
:param is_singleton: if ``True``, reuse existing :class:`ReadWriteLock` instances for the same resolved path
:param loop: event loop for ``run_in_executor``; ``None`` uses the running loop
:param executor: executor for ``run_in_executor``. When ``None`` this lock creates and owns a dedicated
single-thread executor so every operation runs on the same thread (SQLite affinity requires this) and shuts it
down in :meth:`close`. This lock uses a caller-supplied executor as-is and never shuts it down, so after passing
no executor call :meth:`close` to release the owned one.
.. versionadded:: 3.21.0
"""
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,
*,
blocking: bool = True,
is_singleton: bool = True,
loop: asyncio.AbstractEventLoop | None = None,
executor: futures.Executor | None = None,
) -> None:
creator_pid = os.getpid()
self._creator_pid = creator_pid
self._fork_invalidated = False
self._closed = False
_register_fork_object(self)
with _fork_transition():
self._lock = ReadWriteLock(lock_file, timeout, blocking=blocking, is_singleton=is_singleton)
self._loop = loop
self._owns_executor = executor is None
self._executor = executor or ThreadPoolExecutor(max_workers=1)
if os.getpid() != creator_pid: # pragma: forked child
msg = "AsyncReadWriteLock construction cannot continue after fork"
raise RuntimeError(msg)
@property
def lock_file(self) -> str:
"""The path to the lock file."""
return self._lock.lock_file
@property
def timeout(self) -> float:
"""The default timeout."""
return self._lock.timeout
@property
def blocking(self) -> bool:
"""Whether blocking is enabled by default."""
return self._lock.blocking
@property
def loop(self) -> asyncio.AbstractEventLoop | None:
"""The event loop (or ``None`` for the running loop)."""
return self._loop
@property
def executor(self) -> futures.Executor:
"""The executor used for ``run_in_executor`` (a dedicated single-thread one if none was supplied)."""
return self._executor
@asynccontextmanager
async def read_lock(self, timeout: float | None = None, *, blocking: bool | None = None) -> AsyncGenerator[None]:
"""
Async context manager that acquires and releases a shared read lock.
Falls back to instance defaults for *timeout* and *blocking* when ``None``.
:param timeout: maximum wait time in seconds, or ``None`` to use the instance default
:param blocking: if ``False``, raise :class:`~filelock.Timeout` immediately; ``None`` uses the instance default
"""
if timeout is None:
timeout = self._lock.timeout
if blocking is None:
blocking = self._lock.blocking
await self.acquire_read(timeout, blocking=blocking)
body_error: BaseException | None = None
try:
yield
except BaseException as error:
body_error = error
raise
finally:
await self._release_in_context(body_error)
@asynccontextmanager
async def write_lock(self, timeout: float | None = None, *, blocking: bool | None = None) -> AsyncGenerator[None]:
"""
Async context manager that acquires and releases an exclusive write lock.
Falls back to instance defaults for *timeout* and *blocking* when ``None``.
:param timeout: maximum wait time in seconds, or ``None`` to use the instance default
:param blocking: if ``False``, raise :class:`~filelock.Timeout` immediately; ``None`` uses the instance default
"""
if timeout is None:
timeout = self._lock.timeout
if blocking is None:
blocking = self._lock.blocking
await self.acquire_write(timeout, blocking=blocking)
body_error: BaseException | None = None
try:
yield
except BaseException as error:
body_error = error
raise
finally:
await self._release_in_context(body_error)
async def _release_in_context(self, body_error: BaseException | None) -> None:
try:
await self.release()
except BaseException as release_error:
if body_error is not None:
_append_exception_context(release_error, body_error)
raise
async def acquire_read(self, timeout: float = -1, *, blocking: bool = True) -> AsyncAcquireReadWriteReturnProxy:
"""
Acquire a shared read lock.
See :meth:`ReadWriteLock.acquire_read` for full semantics.
:param timeout: maximum wait time in seconds; ``-1`` means block indefinitely
:param blocking: if ``False``, raise :class:`~filelock.Timeout` immediately when the lock is unavailable
:returns: a proxy that can be used as an async context manager to release the lock
:raises RuntimeError: if a write lock is already held on this instance
:raises Timeout: if the lock cannot be acquired within *timeout* seconds
"""
self._raise_if_unusable()
await self._run_acquire(functools.partial(self._lock.acquire_read, timeout, blocking=blocking))
return AsyncAcquireReadWriteReturnProxy(lock=self)
async def acquire_write(self, timeout: float = -1, *, blocking: bool = True) -> AsyncAcquireReadWriteReturnProxy:
"""
Acquire an exclusive write lock.
See :meth:`ReadWriteLock.acquire_write` for full semantics.
:param timeout: maximum wait time in seconds; ``-1`` means block indefinitely
:param blocking: if ``False``, raise :class:`~filelock.Timeout` immediately when the lock is unavailable
:returns: a proxy that can be used as an async context manager to release the lock
:raises RuntimeError: if a read lock is already held, or a write lock is held by a different thread
:raises Timeout: if the lock cannot be acquired within *timeout* seconds
"""
self._raise_if_unusable()
await self._run_acquire(functools.partial(self._lock.acquire_write, timeout, blocking=blocking))
return AsyncAcquireReadWriteReturnProxy(lock=self)
async def release(self, *, force: bool = False) -> None:
"""
Release one level of the current lock.
See :meth:`ReadWriteLock.release` for full semantics.
:param force: if ``True``, release the lock completely regardless of the current lock level
:raises RuntimeError: if no lock is currently held and *force* is ``False``
"""
_ensure_current_process()
if self._inherited: # pragma: needs fork
return
await self._run(self._lock.release, force=force)
async def close(self) -> None:
"""
Release the lock (if held) and close the underlying SQLite connection.
After calling this method, the lock instance is no longer usable.
"""
_ensure_current_process()
if self._inherited: # pragma: needs fork
return
if self._closed:
return
close_future = self._submit(self._lock.close)
try:
await _wait_until_done(close_future)
except asyncio.CancelledError as cancellation:
try:
await _drain_future(close_future)
except BaseException as error: # ruff:ignore[blind-except] # reported with the cancellation below
_raise_cancelled_error(cancellation, error)
self._closed = True
self._shutdown_owned_executor()
raise
_future_result(close_future)
self._closed = True
# Wait for the worker to exit rather than letting it drain in the background: a caller that forks right
# after closing deserves a single-threaded process, and os.fork warns about any surviving thread.
if self._owns_executor:
await asyncio.to_thread(functools.partial(self._executor.shutdown, wait=True))
async def _run_acquire(self, acquire: Callable[[], AcquireReturnProxy]) -> None:
acquire_future = self._submit(acquire)
try:
await _wait_until_done(acquire_future)
except asyncio.CancelledError as cancellation:
try:
await _drain_future(acquire_future)
except BaseException as error: # ruff:ignore[blind-except] # reported with the cancellation below
_raise_cancelled_error(cancellation, error)
try:
await _drain_future(self._submit(self._lock.release))
except BaseException as error: # ruff:ignore[blind-except] # reported with the cancellation below
_raise_cancelled_error(cancellation, error)
raise
_future_result(acquire_future)
async def _run(self, func: Callable[_P, _R], *args: _P.args, **kwargs: _P.kwargs) -> _R:
future = self._submit(func, *args, **kwargs)
try:
await _wait_until_done(future)
except asyncio.CancelledError as cancellation:
try:
await _drain_future(future)
except BaseException as error: # ruff:ignore[blind-except] # reported with the cancellation below
_raise_cancelled_error(cancellation, error)
raise
return _future_result(future)
def _submit(
self, func: Callable[_P, _R], *args: _P.args, **kwargs: _P.kwargs
) -> asyncio.Future[_BackendOutcome[_R]]:
return (self._loop or asyncio.get_running_loop()).run_in_executor(
self._executor,
_capture_call,
functools.partial(func, *args, **kwargs),
)
def _shutdown_owned_executor(self) -> None:
if self._owns_executor:
self._executor.shutdown(wait=False)
@property
def _inherited(self) -> bool:
return self._fork_invalidated or os.getpid() != self._creator_pid
def _raise_if_unusable(self) -> None:
_ensure_current_process()
if self._inherited: # pragma: needs fork
msg = f"AsyncReadWriteLock on {self.lock_file} was invalidated by fork(); construct a new instance"
raise RuntimeError(msg)
if self._closed:
msg = "Cannot operate on a closed database."
raise sqlite3.ProgrammingError(msg)
def _reset_after_fork_in_child(self) -> None: # pragma: forked child
self._fork_invalidated = True
def __del__(self) -> None:
# Safety net when close() was never called: shut down the executor we own so its worker thread does not
# outlive the lock. shutdown(wait=False) never blocks.
if os.getpid() == getattr(self, "_creator_pid", None) and getattr(self, "_owns_executor", False):
self._executor.shutdown(wait=False)
class AsyncAcquireReadWriteReturnProxy:
"""Context-aware object that releases the async read/write lock on exit."""
def __init__(self, lock: AsyncReadWriteLock) -> None:
self.lock = lock
async def __aenter__(self) -> AsyncReadWriteLock:
return self.lock
async def __aexit__(
self,
exc_type: type[BaseException] | None,
exc_value: BaseException | None,
traceback: TracebackType | None,
) -> None:
await self.lock.release()
__all__ = [
"AsyncAcquireReadWriteReturnProxy",
"AsyncReadWriteLock",
]
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