"""Utilities related to asyncio and its support in Scrapy."""
from __future__ import annotations
import asyncio
import logging
import time
from collections.abc import AsyncIterator, Callable, Coroutine, Iterable
from typing import TYPE_CHECKING, Any, Concatenate, ParamSpec, TypeVar
from twisted.internet.defer import Deferred
from twisted.internet.task import LoopingCall
from scrapy.utils.asyncgen import as_async_generator
from scrapy.utils.reactor import is_asyncio_reactor_installed, is_reactor_installed
if TYPE_CHECKING:
from twisted.internet.base import DelayedCall
# typing.Self, typing.TypeVarTuple and typing.Unpack require Python 3.11
from typing_extensions import Self, TypeVarTuple, Unpack
_Ts = TypeVarTuple("_Ts")
_T = TypeVar("_T")
_P = ParamSpec("_P")
logger = logging.getLogger(__name__)
[docs]
def is_asyncio_available() -> bool:
"""Check if it's possible to call asyncio code that relies on the asyncio event loop.
.. versionadded:: 2.14
Currently this function is identical to
:func:`scrapy.utils.reactor.is_asyncio_reactor_installed`: it returns
``True`` if the Twisted reactor that is installed is
:class:`~twisted.internet.asyncioreactor.AsyncioSelectorReactor`, returns
``False`` if a different reactor is installed, and raises a
:exc:`RuntimeError` if no reactor is installed. In a future Scrapy version,
when Scrapy supports running without a Twisted reactor, this function will
also return ``True`` when running in that mode, so code that doesn't
directly require a Twisted reactor should use this function instead of
:func:`~scrapy.utils.reactor.is_asyncio_reactor_installed`.
When this returns ``True``, an asyncio loop is installed and used by
Scrapy. It's possible to call functions that require it, such as
:func:`asyncio.sleep`, and await on :class:`asyncio.Future` objects in
Scrapy-related code.
When this returns ``False``, a non-asyncio Twisted reactor is installed.
It's not possible to use asyncio features that require an asyncio event
loop or await on :class:`asyncio.Future` objects in Scrapy-related code,
but it's possible to await on :class:`~twisted.internet.defer.Deferred`
objects.
"""
if not is_reactor_installed():
raise RuntimeError(
"is_asyncio_available() called without an installed reactor."
)
return is_asyncio_reactor_installed()
async def _parallel_asyncio(
iterable: Iterable[_T] | AsyncIterator[_T],
count: int,
callable_: Callable[Concatenate[_T, _P], Coroutine[Any, Any, None]],
*args: _P.args,
**kwargs: _P.kwargs,
) -> None:
"""Execute a callable over the objects in the given iterable, in parallel,
using no more than ``count`` concurrent calls.
This function is only used in
:meth:`scrapy.core.scraper.Scraper.handle_spider_output_async` and so it
assumes that neither *callable* nor iterating *iterable* will raise an
exception.
"""
queue: asyncio.Queue[_T | None] = asyncio.Queue(count * 2)
async def worker() -> None:
while True:
item = await queue.get()
if item is None:
break
try:
await callable_(item, *args, **kwargs)
finally:
queue.task_done()
async def fill_queue() -> None:
async for item in as_async_generator(iterable):
await queue.put(item)
for _ in range(count):
await queue.put(None)
fill_task = asyncio.create_task(fill_queue())
work_tasks = [asyncio.create_task(worker()) for _ in range(count)]
await asyncio.wait([fill_task, *work_tasks])
class AsyncioLoopingCall:
"""A simple implementation of a periodic call using asyncio, keeping
some API and behavior compatibility with the Twisted ``LoopingCall``.
The function is called every *interval* seconds, independent of the finish
time of the previous call. If the function is still running when it's time
to call it again, calls are skipped until the function finishes.
The function must not return a coroutine or a ``Deferred``.
"""
def __init__(self, func: Callable[_P, _T], *args: _P.args, **kwargs: _P.kwargs):
self._func: Callable[_P, _T] = func
self._args: tuple[Any, ...] = args
self._kwargs: dict[str, Any] = kwargs
self._task: asyncio.Task | None = None
self.interval: float | None = None
self._start_time: float | None = None
@property
def running(self) -> bool:
return self._start_time is not None
def start(self, interval: float, now: bool = True) -> None:
"""Start calling the function every *interval* seconds.
:param interval: The interval in seconds between calls.
:type interval: float
:param now: If ``True``, also call the function immediately.
:type now: bool
"""
if self.running:
raise RuntimeError("AsyncioLoopingCall already running")
if interval <= 0:
raise ValueError("Interval must be greater than 0")
self.interval = interval
self._start_time = time.time()
if now:
self._call()
loop = asyncio.get_event_loop()
self._task = loop.create_task(self._loop())
def _to_sleep(self) -> float:
"""Return the time to sleep until the next call."""
assert self.interval is not None
assert self._start_time is not None
now = time.time()
running_for = now - self._start_time
return self.interval - (running_for % self.interval)
async def _loop(self) -> None:
"""Run an infinite loop that calls the function periodically."""
while self.running:
await asyncio.sleep(self._to_sleep())
self._call()
def stop(self) -> None:
"""Stop the periodic calls."""
self.interval = self._start_time = None
if self._task is not None:
self._task.cancel()
self._task = None
def _call(self) -> None:
"""Execute the function."""
try:
result = self._func(*self._args, **self._kwargs)
except Exception:
logger.exception("Error calling the AsyncioLoopingCall function")
self.stop()
else:
if isinstance(result, (Coroutine, Deferred)):
self.stop()
raise TypeError(
"The AsyncioLoopingCall function must not return a coroutine or a Deferred"
)
def create_looping_call(
func: Callable[_P, _T], *args: _P.args, **kwargs: _P.kwargs
) -> AsyncioLoopingCall | LoopingCall:
"""Create an instance of a looping call class.
This creates an instance of :class:`AsyncioLoopingCall` or
:class:`LoopingCall`, depending on whether asyncio support is available.
"""
if is_asyncio_available():
return AsyncioLoopingCall(func, *args, **kwargs)
return LoopingCall(func, *args, **kwargs)
def call_later(
delay: float, func: Callable[[Unpack[_Ts]], object], *args: Unpack[_Ts]
) -> CallLaterResult:
"""Schedule a function to be called after a delay.
This uses either ``loop.call_later()`` or ``reactor.callLater()``, depending
on whether asyncio support is available.
"""
if is_asyncio_available():
loop = asyncio.get_event_loop()
return CallLaterResult.from_asyncio(loop.call_later(delay, func, *args))
from twisted.internet import reactor
return CallLaterResult.from_twisted(reactor.callLater(delay, func, *args))
class CallLaterResult:
"""An universal result for :func:`call_later`, wrapping either
:class:`asyncio.TimerHandle` or :class:`twisted.internet.base.DelayedCall`.
The provided API is close to the :class:`asyncio.TimerHandle` one: there is
no ``active()`` (as there is no such public API in
:class:`asyncio.TimerHandle`) but ``cancel()`` can be called on already
called or cancelled instances.
"""
_timer_handle: asyncio.TimerHandle | None = None
_delayed_call: DelayedCall | None = None
@classmethod
def from_asyncio(cls, timer_handle: asyncio.TimerHandle) -> Self:
"""Create a CallLaterResult from an asyncio TimerHandle."""
o = cls()
o._timer_handle = timer_handle
return o
@classmethod
def from_twisted(cls, delayed_call: DelayedCall) -> Self:
"""Create a CallLaterResult from a Twisted DelayedCall."""
o = cls()
o._delayed_call = delayed_call
return o
def cancel(self) -> None:
"""Cancel the underlying delayed call.
Does nothing if the delayed call was already called or cancelled.
"""
if self._timer_handle:
self._timer_handle.cancel()
self._timer_handle = None
elif self._delayed_call and self._delayed_call.active():
self._delayed_call.cancel()
self._delayed_call = None