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# Copyright (C) 2023 The Qt Company Ltd.
# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
from . import events
from . import futures
import asyncio
import collections.abc
import concurrent.futures
import contextvars
import typing
class QAsyncioTask(futures.QAsyncioFuture):
""" https://docs.python.org/3/library/asyncio-task.html """
def __init__(self, coro: typing.Union[collections.abc.Generator, collections.abc.Coroutine], *,
loop: typing.Optional["events.QAsyncioEventLoop"] = None,
name: typing.Optional[str] = None,
context: typing.Optional[contextvars.Context] = None) -> None:
super().__init__(loop=loop, context=context)
self._coro = coro # The coroutine for which this task was created.
self._name = name if name else "QtTask"
# The task creates a handle for its coroutine. The handle enqueues the
# task's step function as its callback in the event loop.
self._handle = self._loop.call_soon(self._step, context=self._context)
# The task step function executes the coroutine until it finishes,
# raises an exception or returns a future. If a future was returned,
# the task will await its completion (or exception).
self._future_to_await: typing.Optional[asyncio.Future] = None
self._cancelled = False
self._cancel_message: typing.Optional[str] = None
# https://docs.python.org/3/library/asyncio-extending.html#task-lifetime-support
asyncio._register_task(self) # type: ignore[arg-type]
def __repr__(self) -> str:
if self._state == futures.QAsyncioFuture.FutureState.PENDING:
state = "Pending"
elif self._state == futures.QAsyncioFuture.FutureState.DONE_WITH_RESULT:
state = "Done"
elif self._state == futures.QAsyncioFuture.FutureState.DONE_WITH_EXCEPTION:
state = f"Done with exception ({repr(self._exception)})"
elif self._state == futures.QAsyncioFuture.FutureState.CANCELLED:
state = "Cancelled"
return f"Task '{self.get_name()}' with state: {state}"
class QtTaskApiMisuseError(Exception):
pass
def set_result(self, result: typing.Any) -> None: # type: ignore[override]
# This function is not inherited from the Future APIs.
raise QAsyncioTask.QtTaskApiMisuseError("Tasks cannot set results")
def set_exception(self, exception: typing.Any) -> None: # type: ignore[override]
# This function is not inherited from the Future APIs.
raise QAsyncioTask.QtTaskApiMisuseError("Tasks cannot set exceptions")
def _step(self,
exception_or_future: typing.Union[
BaseException, futures.QAsyncioFuture, None] = None) -> None:
"""
The step function is the heart of a task. It is scheduled in the event
loop repeatedly, executing the coroutine "step" by "step" (i.e.,
iterating through the asynchronous generator) until it finishes with an
exception or successfully. Each step can optionally receive an
exception or a future as a result from a previous step to handle.
"""
if self.done():
return
result = None
self._future_to_await = None
if asyncio.futures.isfuture(exception_or_future):
try:
exception_or_future.result()
except BaseException as e:
exception_or_future = e
try:
asyncio._enter_task(self._loop, self) # type: ignore[arg-type]
# It is at this point that the coroutine is resumed for the current
# step (i.e. asynchronous generator iteration). It will now be
# executed until it yields (and potentially returns a future),
# raises an exception, is cancelled, or finishes successfully.
if isinstance(exception_or_future, BaseException):
# If the coroutine doesn't handle this exception, it propagates
# to the caller.
result = self._coro.throw(exception_or_future)
else:
result = self._coro.send(None)
except StopIteration as e:
self._state = futures.QAsyncioFuture.FutureState.DONE_WITH_RESULT
self._result = e.value
except (concurrent.futures.CancelledError, asyncio.exceptions.CancelledError) as e:
self._state = futures.QAsyncioFuture.FutureState.CANCELLED
self._exception = e
except BaseException as e:
self._state = futures.QAsyncioFuture.FutureState.DONE_WITH_EXCEPTION
self._exception = e
else:
if asyncio.futures.isfuture(result):
# If the coroutine yields a future, the task will await its
# completion, and at that point the step function will be
# called again.
result.add_done_callback(
self._step, context=self._context) # type: ignore[arg-type]
self._future_to_await = result
if self._cancelled:
# If the task was cancelled, then a new future should be
# cancelled as well. Otherwise, in some scenarios like
# a loop inside the task and with bad timing, if the new
# future is not cancelled, the task would continue running
# in this loop despite having been cancelled. This bad
# timing can occur especially if the first future finishes
# very quickly.
self._future_to_await.cancel(self._cancel_message)
elif result is None:
# If no future was yielded, we schedule the step function again
# without any arguments.
self._loop.call_soon(self._step, context=self._context)
else:
# This is not supposed to happen.
exception = RuntimeError(f"Bad task result: {result}")
self._loop.call_soon(self._step, exception, context=self._context)
finally:
asyncio._leave_task(self._loop, self) # type: ignore[arg-type]
if self._exception:
self._loop.call_exception_handler({
"message": (str(self._exception) if self._exception
else "An exception occurred during task "
"execution"),
"exception": self._exception,
"task": self,
"future": (exception_or_future
if asyncio.futures.isfuture(exception_or_future)
else None)
})
if self.done():
self._schedule_callbacks()
# https://docs.python.org/3/library/asyncio-extending.html#task-lifetime-support
asyncio._unregister_task(self) # type: ignore[arg-type]
def get_stack(self, *, limit=None) -> typing.List[typing.Any]:
# TODO
raise NotImplementedError("QtTask.get_stack is not implemented")
def print_stack(self, *, limit=None, file=None) -> None:
# TODO
raise NotImplementedError("QtTask.print_stack is not implemented")
def get_coro(self) -> typing.Union[collections.abc.Generator, collections.abc.Coroutine]:
return self._coro
def get_name(self) -> str:
return self._name
def set_name(self, value) -> None:
self._name = str(value)
def cancel(self, msg: typing.Optional[str] = None) -> bool:
if self.done():
return False
self._cancel_message = msg
self._handle.cancel()
if self._future_to_await is not None:
# A task that is awaiting a future must also cancel this future in
# order for the cancellation to be successful.
self._future_to_await.cancel(msg)
self._cancelled = True
return True
def uncancel(self) -> None:
# TODO
raise NotImplementedError("QtTask.uncancel is not implemented")
def cancelling(self) -> bool:
# TODO
raise NotImplementedError("QtTask.cancelling is not implemented")
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