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Diffstat (limited to 'pydis_core/utils/scheduling.py')
| -rw-r--r-- | pydis_core/utils/scheduling.py | 252 |
1 files changed, 252 insertions, 0 deletions
diff --git a/pydis_core/utils/scheduling.py b/pydis_core/utils/scheduling.py new file mode 100644 index 00000000..eced4a3d --- /dev/null +++ b/pydis_core/utils/scheduling.py @@ -0,0 +1,252 @@ +"""Generic python scheduler.""" + +import asyncio +import contextlib +import inspect +import typing +from collections import abc +from datetime import datetime +from functools import partial + +from pydis_core.utils import logging + + +class Scheduler: + """ + Schedule the execution of coroutines and keep track of them. + + When instantiating a :obj:`Scheduler`, a name must be provided. This name is used to distinguish the + instance's log messages from other instances. Using the name of the class or module containing + the instance is suggested. + + Coroutines can be scheduled immediately with :obj:`schedule` or in the future with :obj:`schedule_at` + or :obj:`schedule_later`. A unique ID is required to be given in order to keep track of the + resulting Tasks. Any scheduled task can be cancelled prematurely using :obj:`cancel` by providing + the same ID used to schedule it. + + The ``in`` operator is supported for checking if a task with a given ID is currently scheduled. + + Any exception raised in a scheduled task is logged when the task is done. + """ + + def __init__(self, name: str): + """ + Initialize a new :obj:`Scheduler` instance. + + Args: + name: The name of the :obj:`Scheduler`. Used in logging, and namespacing. + """ + self.name = name + + self._log = logging.get_logger(f"{__name__}.{name}") + self._scheduled_tasks: dict[abc.Hashable, asyncio.Task] = {} + + def __contains__(self, task_id: abc.Hashable) -> bool: + """ + Return :obj:`True` if a task with the given ``task_id`` is currently scheduled. + + Args: + task_id: The task to look for. + + Returns: + :obj:`True` if the task was found. + """ + return task_id in self._scheduled_tasks + + def schedule(self, task_id: abc.Hashable, coroutine: abc.Coroutine) -> None: + """ + Schedule the execution of a ``coroutine``. + + If a task with ``task_id`` already exists, close ``coroutine`` instead of scheduling it. This + prevents unawaited coroutine warnings. Don't pass a coroutine that'll be re-used elsewhere. + + Args: + task_id: A unique ID to create the task with. + coroutine: The function to be called. + """ + self._log.trace(f"Scheduling task #{task_id}...") + + msg = f"Cannot schedule an already started coroutine for #{task_id}" + assert inspect.getcoroutinestate(coroutine) == "CORO_CREATED", msg + + if task_id in self._scheduled_tasks: + self._log.debug(f"Did not schedule task #{task_id}; task was already scheduled.") + coroutine.close() + return + + task = asyncio.create_task(coroutine, name=f"{self.name}_{task_id}") + task.add_done_callback(partial(self._task_done_callback, task_id)) + + self._scheduled_tasks[task_id] = task + self._log.debug(f"Scheduled task #{task_id} {id(task)}.") + + def schedule_at(self, time: datetime, task_id: abc.Hashable, coroutine: abc.Coroutine) -> None: + """ + Schedule ``coroutine`` to be executed at the given ``time``. + + If ``time`` is timezone aware, then use that timezone to calculate now() when subtracting. + If ``time`` is naïve, then use UTC. + + If ``time`` is in the past, schedule ``coroutine`` immediately. + + If a task with ``task_id`` already exists, close ``coroutine`` instead of scheduling it. This + prevents unawaited coroutine warnings. Don't pass a coroutine that'll be re-used elsewhere. + + Args: + time: The time to start the task. + task_id: A unique ID to create the task with. + coroutine: The function to be called. + """ + now_datetime = datetime.now(time.tzinfo) if time.tzinfo else datetime.utcnow() + delay = (time - now_datetime).total_seconds() + if delay > 0: + coroutine = self._await_later(delay, task_id, coroutine) + + self.schedule(task_id, coroutine) + + def schedule_later( + self, + delay: typing.Union[int, float], + task_id: abc.Hashable, + coroutine: abc.Coroutine + ) -> None: + """ + Schedule ``coroutine`` to be executed after ``delay`` seconds. + + If a task with ``task_id`` already exists, close ``coroutine`` instead of scheduling it. This + prevents unawaited coroutine warnings. Don't pass a coroutine that'll be re-used elsewhere. + + Args: + delay: How long to wait before starting the task. + task_id: A unique ID to create the task with. + coroutine: The function to be called. + """ + self.schedule(task_id, self._await_later(delay, task_id, coroutine)) + + def cancel(self, task_id: abc.Hashable) -> None: + """ + Unschedule the task identified by ``task_id``. Log a warning if the task doesn't exist. + + Args: + task_id: The task's unique ID. + """ + self._log.trace(f"Cancelling task #{task_id}...") + + try: + task = self._scheduled_tasks.pop(task_id) + except KeyError: + self._log.warning(f"Failed to unschedule {task_id} (no task found).") + else: + task.cancel() + + self._log.debug(f"Unscheduled task #{task_id} {id(task)}.") + + def cancel_all(self) -> None: + """Unschedule all known tasks.""" + self._log.debug("Unscheduling all tasks") + + for task_id in self._scheduled_tasks.copy(): + self.cancel(task_id) + + async def _await_later( + self, + delay: typing.Union[int, float], + task_id: abc.Hashable, + coroutine: abc.Coroutine + ) -> None: + """Await ``coroutine`` after ``delay`` seconds.""" + try: + self._log.trace(f"Waiting {delay} seconds before awaiting coroutine for #{task_id}.") + await asyncio.sleep(delay) + + # Use asyncio.shield to prevent the coroutine from cancelling itself. + self._log.trace(f"Done waiting for #{task_id}; now awaiting the coroutine.") + await asyncio.shield(coroutine) + finally: + # Close it to prevent unawaited coroutine warnings, + # which would happen if the task was cancelled during the sleep. + # Only close it if it's not been awaited yet. This check is important because the + # coroutine may cancel this task, which would also trigger the finally block. + state = inspect.getcoroutinestate(coroutine) + if state == "CORO_CREATED": + self._log.debug(f"Explicitly closing the coroutine for #{task_id}.") + coroutine.close() + else: + self._log.debug(f"Finally block reached for #{task_id}; {state=}") + + def _task_done_callback(self, task_id: abc.Hashable, done_task: asyncio.Task) -> None: + """ + Delete the task and raise its exception if one exists. + + If ``done_task`` and the task associated with ``task_id`` are different, then the latter + will not be deleted. In this case, a new task was likely rescheduled with the same ID. + """ + self._log.trace(f"Performing done callback for task #{task_id} {id(done_task)}.") + + scheduled_task = self._scheduled_tasks.get(task_id) + + if scheduled_task and done_task is scheduled_task: + # A task for the ID exists and is the same as the done task. + # Since this is the done callback, the task is already done so no need to cancel it. + self._log.trace(f"Deleting task #{task_id} {id(done_task)}.") + del self._scheduled_tasks[task_id] + elif scheduled_task: + # A new task was likely rescheduled with the same ID. + self._log.debug( + f"The scheduled task #{task_id} {id(scheduled_task)} " + f"and the done task {id(done_task)} differ." + ) + elif not done_task.cancelled(): + self._log.warning( + f"Task #{task_id} not found while handling task {id(done_task)}! " + f"A task somehow got unscheduled improperly (i.e. deleted but not cancelled)." + ) + + with contextlib.suppress(asyncio.CancelledError): + exception = done_task.exception() + # Log the exception if one exists. + if exception: + self._log.error(f"Error in task #{task_id} {id(done_task)}!", exc_info=exception) + + +TASK_RETURN = typing.TypeVar("TASK_RETURN") + + +def create_task( + coro: abc.Coroutine[typing.Any, typing.Any, TASK_RETURN], + *, + suppressed_exceptions: tuple[type[Exception], ...] = (), + event_loop: typing.Optional[asyncio.AbstractEventLoop] = None, + **kwargs, +) -> asyncio.Task[TASK_RETURN]: + """ + Wrapper for creating an :obj:`asyncio.Task` which logs exceptions raised in the task. + + If the ``event_loop`` kwarg is provided, the task is created from that event loop, + otherwise the running loop is used. + + Args: + coro: The function to call. + suppressed_exceptions: Exceptions to be handled by the task. + event_loop (:obj:`asyncio.AbstractEventLoop`): The loop to create the task from. + kwargs: Passed to :py:func:`asyncio.create_task`. + + Returns: + asyncio.Task: The wrapped task. + """ + if event_loop is not None: + task = event_loop.create_task(coro, **kwargs) + else: + task = asyncio.create_task(coro, **kwargs) + task.add_done_callback(partial(_log_task_exception, suppressed_exceptions=suppressed_exceptions)) + return task + + +def _log_task_exception(task: asyncio.Task, *, suppressed_exceptions: tuple[type[Exception], ...]) -> None: + """Retrieve and log the exception raised in ``task`` if one exists.""" + with contextlib.suppress(asyncio.CancelledError): + exception = task.exception() + # Log the exception if one exists. + if exception and not isinstance(exception, suppressed_exceptions): + log = logging.get_logger(__name__) + log.error(f"Error in task {task.get_name()} {id(task)}!", exc_info=exception) |