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from abc import ABCMeta, abstractmethod
from collections.abc import Iterable
from inspect import iscoroutinefunction
from typing import Any, TypeVar
from asgiref.sync import sync_to_async
from django.conf import settings
from django.core import checks
from django.utils import timezone
from django.utils.inspect import get_func_args
from typing_extensions import ParamSpec
from django_tasks.base import (
DEFAULT_TASK_PRIORITY,
TASK_MAX_PRIORITY,
TASK_MIN_PRIORITY,
Task,
TaskResult,
)
from django_tasks.exceptions import InvalidTaskError
from django_tasks.utils import is_module_level_function
T = TypeVar("T")
P = ParamSpec("P")
class BaseTaskBackend(metaclass=ABCMeta):
alias: str
task_class = Task
supports_defer = False
"""Does the backend support Tasks to be enqueued with the run_after attribute?"""
supports_async_task = False
"""Does the backend support coroutines to be enqueued?"""
supports_get_result = False
"""Does the backend support results being retrieved (from any thread / process)?"""
supports_priority = False
"""Does the backend support tasks being executed in a given priority order?"""
def __init__(self, alias: str, params: dict) -> None:
from django_tasks import DEFAULT_TASK_QUEUE_NAME
self.alias = alias
self.queues = set(params.get("QUEUES", [DEFAULT_TASK_QUEUE_NAME]))
self.options = params.get("OPTIONS", {})
def validate_task(self, task: Task) -> None:
"""
Determine whether the provided Task can be executed by the backend.
"""
if not is_module_level_function(task.func):
raise InvalidTaskError("Task function must be defined at a module level.")
if not self.supports_async_task and iscoroutinefunction(task.func):
raise InvalidTaskError("Backend does not support async tasks.")
task_func_args = get_func_args(task.func)
if task.takes_context and (
not task_func_args or task_func_args[0] != "context"
):
raise InvalidTaskError(
"Task takes context but does not have a first argument of 'context'."
)
if not self.supports_priority and task.priority != DEFAULT_TASK_PRIORITY:
raise InvalidTaskError(
"Backend does not support setting priority of tasks."
)
if (
task.priority < TASK_MIN_PRIORITY
or task.priority > TASK_MAX_PRIORITY
or int(task.priority) != task.priority
):
raise InvalidTaskError(
f"priority must be a whole number between {TASK_MIN_PRIORITY} and {TASK_MAX_PRIORITY}."
)
if not self.supports_defer and task.run_after is not None:
raise InvalidTaskError("Backend does not support run_after.")
if (
settings.USE_TZ
and task.run_after is not None
and not timezone.is_aware(task.run_after)
):
raise InvalidTaskError("run_after must be an aware datetime.")
if self.queues and task.queue_name not in self.queues:
raise InvalidTaskError(
f"Queue '{task.queue_name}' is not valid for backend."
)
@abstractmethod
def enqueue(
self,
task: Task[P, T],
args: P.args, # type:ignore[valid-type]
kwargs: P.kwargs, # type:ignore[valid-type]
) -> TaskResult[T]:
"""
Queue up a task to be executed
"""
async def aenqueue(
self,
task: Task[P, T],
args: P.args, # type:ignore[valid-type]
kwargs: P.kwargs, # type:ignore[valid-type]
) -> TaskResult[T]:
"""
Queue up a task function (or coroutine) to be executed
"""
return await sync_to_async(self.enqueue, thread_sensitive=True)(
task=task, args=args, kwargs=kwargs
)
def get_result(self, result_id: str) -> TaskResult:
"""
Retrieve a result by id if it exists, otherwise raise
ResultDoesNotExist.
"""
raise NotImplementedError(
"This backend does not support retrieving or refreshing results."
)
async def aget_result(self, result_id: str) -> TaskResult:
"""See get_result()."""
return await sync_to_async(self.get_result, thread_sensitive=True)(
result_id=result_id
)
def check(self, **kwargs: Any) -> Iterable[checks.CheckMessage]:
return []
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