# util/concurrency.py # Copyright (C) 2005-2026 the SQLAlchemy authors and contributors # # # This module is part of SQLAlchemy and is released under # the MIT License: https://www.opensource.org/licenses/mit-license.php # mypy: allow-untyped-defs, allow-untyped-calls """asyncio-related concurrency functions.""" from __future__ import annotations import asyncio import sys from typing import Any from typing import Awaitable from typing import Callable from typing import Coroutine from typing import NoReturn from typing import TYPE_CHECKING from typing import TypeGuard from typing import TypeVar from .langhelpers import memoized_property from .. import exc _T = TypeVar("_T") def is_exit_exception(e: BaseException) -> bool: # note asyncio.CancelledError is already BaseException # so was an exit exception in any case return not isinstance(e, Exception) or isinstance( e, (asyncio.TimeoutError, asyncio.CancelledError) ) _ERROR_MESSAGE = ( "The SQLAlchemy asyncio module requires that the Python 'greenlet' " "library is installed. In order to ensure this dependency is " "available, use the 'sqlalchemy[asyncio]' install target: " "'pip install sqlalchemy[asyncio]'" ) def _not_implemented(*arg: Any, **kw: Any) -> NoReturn: raise ImportError(_ERROR_MESSAGE) class _concurrency_shim_cls: """Late import shim for greenlet""" __slots__ = ( "_has_greenlet", "greenlet", "_AsyncIoGreenlet", "getcurrent", ) def _initialize(self, *, raise_: bool = True) -> None: """Import greenlet and initialize the class""" if "greenlet" in globals(): return if not TYPE_CHECKING: global getcurrent, greenlet, _AsyncIoGreenlet global _has_gr_context try: from greenlet import getcurrent from greenlet import greenlet except ImportError as e: if not TYPE_CHECKING: # set greenlet in the global scope to prevent re-init greenlet = None self._has_greenlet = False self._initialize_no_greenlet() if raise_: raise ImportError(_ERROR_MESSAGE) from e else: self._has_greenlet = True # If greenlet.gr_context is present in current version of greenlet, # it will be set with the current context on creation. # Refs: https://github.com/python-greenlet/greenlet/pull/198 _has_gr_context = hasattr(getcurrent(), "gr_context") # implementation based on snaury gist at # https://gist.github.com/snaury/202bf4f22c41ca34e56297bae5f33fef # Issue for context: https://github.com/python-greenlet/greenlet/issues/173 # noqa: E501 class _AsyncIoGreenlet(greenlet): dead: bool __sqlalchemy_greenlet_provider__ = True def __init__(self, fn: Callable[..., Any], driver: greenlet): greenlet.__init__(self, fn, driver) if _has_gr_context: self.gr_context = driver.gr_context self.greenlet = greenlet self.getcurrent = getcurrent self._AsyncIoGreenlet = _AsyncIoGreenlet def _initialize_no_greenlet(self): self.getcurrent = _not_implemented self.greenlet = _not_implemented # type: ignore[assignment] self._AsyncIoGreenlet = _not_implemented # type: ignore[assignment] def __getattr__(self, key: str) -> Any: if key in self.__slots__: self._initialize() return getattr(self, key) else: raise AttributeError(key) _concurrency_shim = _concurrency_shim_cls() if TYPE_CHECKING: _T_co = TypeVar("_T_co", covariant=True) def iscoroutine( awaitable: Awaitable[_T_co], ) -> TypeGuard[Coroutine[Any, Any, _T_co]]: ... else: iscoroutine = asyncio.iscoroutine def _safe_cancel_awaitable(awaitable: Awaitable[Any]) -> None: # https://docs.python.org/3/reference/datamodel.html#coroutine.close if iscoroutine(awaitable): awaitable.close() def in_greenlet() -> bool: current = _concurrency_shim.getcurrent() return getattr(current, "__sqlalchemy_greenlet_provider__", False) def await_(awaitable: Awaitable[_T]) -> _T: """Awaits an async function in a sync method. The sync method must be inside a :func:`greenlet_spawn` context. :func:`await_` calls cannot be nested. :param awaitable: The coroutine to call. """ # this is called in the context greenlet while running fn current = _concurrency_shim.getcurrent() if not getattr(current, "__sqlalchemy_greenlet_provider__", False): _safe_cancel_awaitable(awaitable) raise exc.MissingGreenlet( "greenlet_spawn has not been called; can't call await_() " "here. Was IO attempted in an unexpected place?" ) # returns the control to the driver greenlet passing it # a coroutine to run. Once the awaitable is done, the driver greenlet # switches back to this greenlet with the result of awaitable that is # then returned to the caller (or raised as error) assert current.parent return current.parent.switch(awaitable) # type: ignore[no-any-return] await_only = await_ # old name. deprecated on 2.2 async def greenlet_spawn( fn: Callable[..., _T], *args: Any, _require_await: bool = False, **kwargs: Any, ) -> _T: """Runs a sync function ``fn`` in a new greenlet. The sync function can then use :func:`await_` to wait for async functions. :param fn: The sync callable to call. :param \\*args: Positional arguments to pass to the ``fn`` callable. :param \\*\\*kwargs: Keyword arguments to pass to the ``fn`` callable. """ result: Any context = _concurrency_shim._AsyncIoGreenlet( fn, _concurrency_shim.getcurrent() ) # runs the function synchronously in gl greenlet. If the execution # is interrupted by await_, context is not dead and result is a # coroutine to wait. If the context is dead the function has # returned, and its result can be returned. switch_occurred = False result = context.switch(*args, **kwargs) while not context.dead: switch_occurred = True try: # wait for a coroutine from await_ and then return its # result back to it. value = await result except BaseException: # this allows an exception to be raised within # the moderated greenlet so that it can continue # its expected flow. result = context.throw(*sys.exc_info()) else: result = context.switch(value) if _require_await and not switch_occurred: raise exc.AwaitRequired( "The current operation required an async execution but none was " "detected. This will usually happen when using a non compatible " "DBAPI driver. Please ensure that an async DBAPI is used." ) return result # type: ignore[no-any-return] class AsyncAdaptedLock: @memoized_property def mutex(self) -> asyncio.Lock: # there should not be a race here for coroutines creating the # new lock as we are not using await, so therefore no concurrency return asyncio.Lock() def __enter__(self) -> bool: # await is used to acquire the lock only after the first calling # coroutine has created the mutex. return await_(self.mutex.acquire()) def __exit__(self, *arg: Any, **kw: Any) -> None: self.mutex.release() class _AsyncUtil: """Asyncio util for test suite/ util only""" def __init__(self) -> None: # runner it lazy so it can be created here self.runner = asyncio.Runner() def run( self, fn: Callable[..., Coroutine[Any, Any, _T]], *args: Any, **kwargs: Any, ) -> _T: """Run coroutine on the loop""" return self.runner.run(fn(*args, **kwargs)) def run_in_greenlet( self, fn: Callable[..., _T], *args: Any, **kwargs: Any ) -> _T: """Run sync function in greenlet. Support nested calls""" _concurrency_shim._initialize(raise_=False) if _concurrency_shim._has_greenlet: if self.runner.get_loop().is_running(): # allow for a wrapped test function to call another assert in_greenlet() return fn(*args, **kwargs) else: return self.runner.run(greenlet_spawn(fn, *args, **kwargs)) else: return fn(*args, **kwargs) def close(self) -> None: self.runner.close()