takahe/stator/models.py
Andrew Godwin 6e88c00969 Don't waste DB rows on bad inbox actors
Seems Sidekiq will keep trying to deliver messages even when the actor
no longer exists?
2022-11-20 14:20:28 -07:00

240 lines
8.1 KiB
Python

import datetime
import pprint
import traceback
from typing import ClassVar, List, Optional, Type, Union, cast
from asgiref.sync import sync_to_async
from django.db import models, transaction
from django.utils import timezone
from django.utils.functional import classproperty
from core import exceptions
from stator.graph import State, StateGraph
class StateField(models.CharField):
"""
A special field that automatically gets choices from a state graph
"""
def __init__(self, graph: Type[StateGraph], **kwargs):
# Sensible default for state length
kwargs.setdefault("max_length", 100)
# Add choices and initial
self.graph = graph
kwargs["choices"] = self.graph.choices
kwargs["default"] = self.graph.initial_state.name
super().__init__(**kwargs)
def deconstruct(self):
name, path, args, kwargs = super().deconstruct()
kwargs["graph"] = self.graph
return name, path, args, kwargs
def get_prep_value(self, value):
if isinstance(value, State):
return value.name
return value
class StatorModel(models.Model):
"""
A model base class that has a state machine backing it, with tasks to work
out when to move the state to the next one.
You need to provide a "state" field as an instance of StateField on the
concrete model yourself.
"""
# If this row is up for transition attempts (which it always is on creation!)
state_ready = models.BooleanField(default=True)
# When the state last actually changed, or the date of instance creation
state_changed = models.DateTimeField(auto_now_add=True)
# When the last state change for the current state was attempted
# (and not successful, as this is cleared on transition)
state_attempted = models.DateTimeField(blank=True, null=True)
# If a lock is out on this row, when it is locked until
# (we don't identify the lock owner, as there's no heartbeats)
state_locked_until = models.DateTimeField(null=True, blank=True)
# Collection of subclasses of us
subclasses: ClassVar[List[Type["StatorModel"]]] = []
class Meta:
abstract = True
def __init_subclass__(cls) -> None:
if cls is not StatorModel:
cls.subclasses.append(cls)
@classproperty
def state_graph(cls) -> Type[StateGraph]:
return cls._meta.get_field("state").graph
@classmethod
async def atransition_schedule_due(cls, now=None) -> models.QuerySet:
"""
Finds instances of this model that need to run and schedule them.
"""
q = models.Q()
for state in cls.state_graph.states.values():
state = cast(State, state)
if not state.externally_progressed:
q = q | models.Q(
(
models.Q(
state_attempted__lte=timezone.now()
- datetime.timedelta(
seconds=cast(float, state.try_interval)
)
)
| models.Q(state_attempted__isnull=True)
),
state=state.name,
)
await cls.objects.filter(q).aupdate(state_ready=True)
@classmethod
def transition_get_with_lock(
cls, number: int, lock_expiry: datetime.datetime
) -> List["StatorModel"]:
"""
Returns up to `number` tasks for execution, having locked them.
"""
with transaction.atomic():
selected = list(
cls.objects.filter(
state_locked_until__isnull=True,
state_ready=True,
state__in=cls.state_graph.automatic_states,
)[:number].select_for_update()
)
cls.objects.filter(pk__in=[i.pk for i in selected]).update(
state_locked_until=lock_expiry
)
return selected
@classmethod
async def atransition_get_with_lock(
cls, number: int, lock_expiry: datetime.datetime
) -> List["StatorModel"]:
return await sync_to_async(cls.transition_get_with_lock)(number, lock_expiry)
@classmethod
async def atransition_clean_locks(cls):
await cls.objects.filter(state_locked_until__lte=timezone.now()).aupdate(
state_locked_until=None
)
def transition_schedule(self):
"""
Adds this instance to the queue to get its state transition attempted.
The scheduler will call this, but you can also call it directly if you
know it'll be ready and want to lower latency.
"""
self.state_ready = True
self.save()
async def atransition_attempt(self) -> Optional[State]:
"""
Attempts to transition the current state by running its handler(s).
"""
current_state = self.state_graph.states[self.state]
# If it's a manual progression state don't even try
# We shouldn't really be here in this case, but it could be a race condition
if current_state.externally_progressed:
print(
f"Warning: trying to progress externally progressed state {self.state}!"
)
return None
try:
next_state = await current_state.handler(self)
except BaseException as e:
await StatorError.acreate_from_instance(self, e)
await exceptions.acapture_exception(e)
traceback.print_exc()
else:
if next_state:
# Ensure it's a State object
if isinstance(next_state, str):
next_state = self.state_graph.states[next_state]
# Ensure it's a child
if next_state not in current_state.children:
raise ValueError(
f"Cannot transition from {current_state} to {next_state} - not a declared transition"
)
await self.atransition_perform(next_state)
return next_state
await self.__class__.objects.filter(pk=self.pk).aupdate(
state_attempted=timezone.now(),
state_locked_until=None,
state_ready=False,
)
return None
def transition_perform(self, state: Union[State, str]):
"""
Transitions the instance to the given state name, forcibly.
"""
if isinstance(state, State):
state = state.name
if state not in self.state_graph.states:
raise ValueError(f"Invalid state {state}")
self.__class__.objects.filter(pk=self.pk).update(
state=state,
state_changed=timezone.now(),
state_attempted=None,
state_locked_until=None,
state_ready=True,
)
atransition_perform = sync_to_async(transition_perform)
class StatorError(models.Model):
"""
Tracks any errors running the transitions.
Meant to be cleaned out regularly. Should probably be a log.
"""
# appname.modelname (lowercased) label for the model this represents
model_label = models.CharField(max_length=200)
# The primary key of that model (probably int or str)
instance_pk = models.CharField(max_length=200)
# The state we were on
state = models.CharField(max_length=200)
# When it happened
date = models.DateTimeField(auto_now_add=True)
# Error name
error = models.TextField()
# Error details
error_details = models.TextField(blank=True, null=True)
@classmethod
async def acreate_from_instance(
cls,
instance: StatorModel,
exception: Optional[BaseException] = None,
):
detail = traceback.format_exc()
if exception and len(exception.args) > 1:
detail += "\n\n" + "\n\n".join(
pprint.pformat(arg) for arg in exception.args
)
return await cls.objects.acreate(
model_label=instance._meta.label_lower,
instance_pk=str(instance.pk),
state=instance.state,
error=str(exception),
error_details=detail,
)