[Sqlalchemy-tickets] Issue #3947: race condition in joined eager load perf enhancement (zzzeek/sqlalchemy)

[Michael B. <iss...@bi...>]

New issue 3947: race condition in joined eager load perf enhancement
https://bitbucket.org/zzzeek/sqlalchemy/issues/3947/race-condition-in-joined-eager-load-perf

Michael Bayer:

e.g. #3915

test:


```
#!python

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()


class A(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)
    bs = relationship("B")

class B(Base):
    __tablename__ = 'b'
    id = Column(Integer, primary_key=True)
    a_id = Column(ForeignKey('a.id'))

e = create_engine("sqlite:///foo.db", echo=False)
Base.metadata.create_all(e)


import threading
import random
import time
import traceback

def work(e):
    s = Session(e)
    while True:
        try:
            s.query(A).options(joinedload(A.bs)).all()
        except Exception as e:
            traceback.print_exc()
            print "Exception: %s" % e
        finally:
            time.sleep(random.random())

def chaos():
    while True:
        time.sleep(.001)
        A.bs.property._get_strategy((("lazy", "joined"),))._aliased_class_pool[:] = []

s = Session(e)
s.add_all([A(bs=[B(), B(), B()])])
s.commit()


threads = [threading.Thread(target=work, args=(e, )) for i in range(20)]
chaos = threading.Thread(target=chaos)

for t in threads:
    t.start()
chaos.start()

```


traceback


```
#!

Traceback (most recent call last):
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/query.py", line 2679, in all
  File "test.py", line 31, in work
    s.query(A).options(joinedload(A.bs)).all()
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/query.py", line 2679, in all
yes
    return list(self)
    return list(self)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/loading.py", line 90, in instances
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/query.py", line 2831, in __iter__
    return self._execute_and_instances(context)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/query.py", line 2854, in _execute_and_instances
    result = conn.execute(querycontext.statement, self._params)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/engine/base.py", line 945, in execute
    util.raise_from_cause(err)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/util/compat.py", line 203, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb, cause=cause)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/loading.py", line 57, in instances
    for query_entity in query._entities
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/query.py", line 3686, in row_processor
    polymorphic_discriminator=self._polymorphic_discriminator
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/loading.py", line 330, in _instance_processor
    context, path, mapper, result, adapter, populators)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/interfaces.py", line 532, in create_row_processor
    return meth(self, multiparams, params)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/sql/elements.py", line 269, in _execute_on_connection
    mapper, result, adapter, populators)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/strategies.py", line 1594, in create_row_processor
    eager_adapter)
    return connection._execute_clauseelement(self, multiparams, params)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/loading.py", line 318, in _instance_processor
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/engine/base.py", line 1053, in _execute_clauseelement
    col = adapter.columns[col]
    compiled_sql, distilled_params
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/sql/util.py", line 713, in __getitem__
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/engine/base.py", line 1189, in _execute_context
    context)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/engine/base.py", line 1393, in _handle_dbapi_exception
    exc_info
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/util/compat.py", line 203, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb, cause=cause)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/engine/base.py", line 1182, in _execute_context
    context)
    self.parent.include_fn and not self.parent.include_fn(key)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/util.py", line 326, in _include_fn
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/engine/default.py", line 504, in do_execute
    entity = elem._annotations.get('parentmapper', None)
AttributeError: 'NoneType' object has no attribute '_annotations'
Exception: 'NoneType' object has no attribute '_annotations'
    cursor.execute(statement, parameters)

```