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__init__.py
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__init__.py
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"""SQLAlchemy result store backend."""
import logging
from contextlib import contextmanager
from vine.utils import wraps
from celery import states
from celery.backends.base import BaseBackend
from celery.exceptions import ImproperlyConfigured
from celery.utils.time import maybe_timedelta
from .models import Task, TaskExtended, TaskSet
from .session import SessionManager
try:
from sqlalchemy.exc import DatabaseError, InvalidRequestError
from sqlalchemy.orm.exc import StaleDataError
except ImportError: # pragma: no cover
raise ImproperlyConfigured(
'The database result backend requires SQLAlchemy to be installed.'
'See https://pypi.org/project/SQLAlchemy/')
logger = logging.getLogger(__name__)
__all__ = ('DatabaseBackend',)
@contextmanager
def session_cleanup(session):
try:
yield
except Exception:
session.rollback()
raise
finally:
session.close()
def retry(fun):
@wraps(fun)
def _inner(*args, **kwargs):
max_retries = kwargs.pop('max_retries', 3)
for retries in range(max_retries):
try:
return fun(*args, **kwargs)
except (DatabaseError, InvalidRequestError, StaleDataError):
logger.warning(
'Failed operation %s. Retrying %s more times.',
fun.__name__, max_retries - retries - 1,
exc_info=True)
if retries + 1 >= max_retries:
raise
return _inner
class DatabaseBackend(BaseBackend):
"""The database result backend."""
# ResultSet.iterate should sleep this much between each pool,
# to not bombard the database with queries.
subpolling_interval = 0.5
task_cls = Task
taskset_cls = TaskSet
def __init__(self, dburi=None, engine_options=None, url=None, **kwargs):
# The `url` argument was added later and is used by
# the app to set backend by url (celery.app.backends.by_url)
super().__init__(expires_type=maybe_timedelta,
url=url, **kwargs)
conf = self.app.conf
if self.extended_result:
self.task_cls = TaskExtended
self.url = url or dburi or conf.database_url
self.engine_options = dict(
engine_options or {},
**conf.database_engine_options or {})
self.short_lived_sessions = kwargs.get(
'short_lived_sessions',
conf.database_short_lived_sessions)
schemas = conf.database_table_schemas or {}
tablenames = conf.database_table_names or {}
self.task_cls.configure(
schema=schemas.get('task'),
name=tablenames.get('task'))
self.taskset_cls.configure(
schema=schemas.get('group'),
name=tablenames.get('group'))
if not self.url:
raise ImproperlyConfigured(
'Missing connection string! Do you have the'
' database_url setting set to a real value?')
@property
def extended_result(self):
return self.app.conf.find_value_for_key('extended', 'result')
def ResultSession(self, session_manager=SessionManager()):
return session_manager.session_factory(
dburi=self.url,
short_lived_sessions=self.short_lived_sessions,
**self.engine_options)
@retry
def _store_result(self, task_id, result, state, traceback=None,
request=None, **kwargs):
"""Store return value and state of an executed task."""
session = self.ResultSession()
with session_cleanup(session):
task = list(session.query(self.task_cls).filter(self.task_cls.task_id == task_id))
task = task and task[0]
if not task:
task = self.task_cls(task_id)
task.task_id = task_id
session.add(task)
session.flush()
self._update_result(task, result, state, traceback=traceback, request=request)
session.commit()
def _update_result(self, task, result, state, traceback=None,
request=None):
meta = self._get_result_meta(result=result, state=state,
traceback=traceback, request=request,
format_date=False, encode=True)
# Exclude the primary key id and task_id columns
# as we should not set it None
columns = [column.name for column in self.task_cls.__table__.columns
if column.name not in {'id', 'task_id'}]
# Iterate through the columns name of the table
# to set the value from meta.
# If the value is not present in meta, set None
for column in columns:
value = meta.get(column)
setattr(task, column, value)
@retry
def _get_task_meta_for(self, task_id):
"""Get task meta-data for a task by id."""
session = self.ResultSession()
with session_cleanup(session):
task = list(session.query(self.task_cls).filter(self.task_cls.task_id == task_id))
task = task and task[0]
if not task:
task = self.task_cls(task_id)
task.status = states.PENDING
task.result = None
data = task.to_dict()
if data.get('args', None) is not None:
data['args'] = self.decode(data['args'])
if data.get('kwargs', None) is not None:
data['kwargs'] = self.decode(data['kwargs'])
return self.meta_from_decoded(data)
@retry
def _save_group(self, group_id, result):
"""Store the result of an executed group."""
session = self.ResultSession()
with session_cleanup(session):
group = self.taskset_cls(group_id, result)
session.add(group)
session.flush()
session.commit()
return result
@retry
def _restore_group(self, group_id):
"""Get meta-data for group by id."""
session = self.ResultSession()
with session_cleanup(session):
group = session.query(self.taskset_cls).filter(
self.taskset_cls.taskset_id == group_id).first()
if group:
return group.to_dict()
@retry
def _delete_group(self, group_id):
"""Delete meta-data for group by id."""
session = self.ResultSession()
with session_cleanup(session):
session.query(self.taskset_cls).filter(
self.taskset_cls.taskset_id == group_id).delete()
session.flush()
session.commit()
@retry
def _forget(self, task_id):
"""Forget about result."""
session = self.ResultSession()
with session_cleanup(session):
session.query(self.task_cls).filter(self.task_cls.task_id == task_id).delete()
session.commit()
def cleanup(self):
"""Delete expired meta-data."""
session = self.ResultSession()
expires = self.expires
now = self.app.now()
with session_cleanup(session):
session.query(self.task_cls).filter(
self.task_cls.date_done < (now - expires)).delete()
session.query(self.taskset_cls).filter(
self.taskset_cls.date_done < (now - expires)).delete()
session.commit()
def __reduce__(self, args=(), kwargs=None):
kwargs = {} if not kwargs else kwargs
kwargs.update(
{'dburi': self.url,
'expires': self.expires,
'engine_options': self.engine_options})
return super().__reduce__(args, kwargs)