automap.prepare() creates classes that are referenced but not mapped, causes errors under concurrency

[sqlalchemy-bot]

Migrated issue, originally created by Michael Bayer (@zzzeek)

demo:

from sqlalchemy import *
from sqlalchemy.orm import configure_mappers
from sqlalchemy.ext.automap import automap_base
import time
import random
import threading


def make_tables(e):
    m = MetaData()
    for i in range(15):
        Table(
            'table_%d' % i,
            m,
            Column('id', Integer, primary_key=True),
            Column('data', String(50)),
            Column(
                't_%d_id' % (i - 1),
                ForeignKey('table_%d.id' % (i - 1))
            ) if i > 4 else None
        )
    m.drop_all(e)
    m.create_all(e)


def automap(e):
    id_ = threading.get_ident()
    Base = automap_base()

    Base.prepare(e, reflect=True)
    print("thread %s prepared!" % id_)

    time.sleep(.01)
    configure_mappers()
    print("thread %s we're good!" % id_)


def chaos():
    while True:
        automap(e)
        time.sleep(random.random())

e = create_engine("mysql://scott:tiger@localhost/test")

make_tables(e)

threads = [threading.Thread(target=chaos) for i in range(30)]
for t in threads:
    t.start()

for t in threads:
    t.join()

output:

thread 139667543086848 prepared!
thread 139667526301440 prepared!
thread 139667559872256 prepared!
Exception in thread Thread-5:
Traceback (most recent call last):
  File "/usr/lib64/python3.6/threading.py", line 916, in _bootstrap_inner
    self.run()
  File "/usr/lib64/python3.6/threading.py", line 864, in run
    self._target(*self._args, **self._kwargs)
  File "test.py", line 40, in chaos
    automap(e)
  File "test.py", line 34, in automap
    configure_mappers()
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/mapper.py", line 3026, in configure_mappers
    raise e
sqlalchemy.exc.InvalidRequestError: One or more mappers failed to initialize - can't proceed with initialization of other mappers. Triggering mapper: 'Mapper|table_14|table_14'. Original exception was: Class 'sqlalchemy.ext.automap.table_13' is not mapped

Exception in thread Thread-3:
Traceback (most recent call last):
  File "/usr/lib64/python3.6/threading.py", line 916, in _bootstrap_inner
    self.run()
  File "/usr/lib64/python3.6/threading.py", line 864, in run
    self._target(*self._args, **self._kwargs)
  File "test.py", line 40, in chaos
    automap(e)
  File "test.py", line 34, in automap
    configure_mappers()
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/mapper.py", line 3029, in configure_mappers
    mapper._post_configure_properties()
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/mapper.py", line 1828, in _post_configure_properties
    prop.init()
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/interfaces.py", line 184, in init
    self.do_init()
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/relationships.py", line 1655, in do_init
    self._process_dependent_arguments()
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/relationships.py", line 1712, in _process_dependent_arguments
    self.target = self.mapper.mapped_table
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/util/langhelpers.py", line 767, in __get__
    obj.__dict__[self.__name__] = result = self.fget(obj)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/relationships.py", line 1634, in mapper
    configure=False)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/base.py", line 426, in class_mapper
    raise exc.UnmappedClassError(class_)
sqlalchemy.orm.exc.UnmappedClassError: Class 'sqlalchemy.ext.automap.table_13' is not mapped

... continues until all threads are done

this can be patched as:

diff --git a/lib/sqlalchemy/ext/automap.py b/lib/sqlalchemy/ext/automap.py
index 30f48fcea..b2fdbf802 100644
--- a/lib/sqlalchemy/ext/automap.py
+++ b/lib/sqlalchemy/ext/automap.py
@@ -518,6 +518,7 @@ from .declarative.base import _DeferredMapperConfig
 from ..sql import and_
 from ..schema import ForeignKeyConstraint
 from ..orm import relationship, backref, interfaces
+from ..orm.mapper import _CONFIGURE_MUTEX
 from .. import util
 
 
@@ -754,49 +755,53 @@ class AutomapBase(object):
                 autoload_replace=False
             )
 
-        table_to_map_config = dict(
-            (m.local_table, m)
-            for m in _DeferredMapperConfig.
-            classes_for_base(cls, sort=False)
-        )
-
-        many_to_many = []
+        _CONFIGURE_MUTEX.acquire()
+        try:
+            table_to_map_config = dict(
+                (m.local_table, m)
+                for m in _DeferredMapperConfig.
+                classes_for_base(cls, sort=False)
+            )
 
-        for table in cls.metadata.tables.values():
-            lcl_m2m, rem_m2m, m2m_const = _is_many_to_many(cls, table)
-            if lcl_m2m is not None:
-                many_to_many.append((lcl_m2m, rem_m2m, m2m_const, table))
-            elif not table.primary_key:
-                continue
-            elif table not in table_to_map_config:
-                mapped_cls = type(
-                    classname_for_table(cls, table.name, table),
-                    (cls, ),
-                    {"__table__": table}
-                )
-                map_config = _DeferredMapperConfig.config_for_cls(mapped_cls)
-                cls.classes[map_config.cls.__name__] = mapped_cls
-                table_to_map_config[table] = map_config
-
-        for map_config in table_to_map_config.values():
-            _relationships_for_fks(cls,
-                                   map_config,
-                                   table_to_map_config,
-                                   collection_class,
-                                   name_for_scalar_relationship,
-                                   name_for_collection_relationship,
-                                   generate_relationship)
-
-        for lcl_m2m, rem_m2m, m2m_const, table in many_to_many:
-            _m2m_relationship(cls, lcl_m2m, rem_m2m, m2m_const, table,
-                              table_to_map_config,
-                              collection_class,
-                              name_for_scalar_relationship,
-                              name_for_collection_relationship,
-                              generate_relationship)
-
-        for map_config in _DeferredMapperConfig.classes_for_base(cls):
-            map_config.map()
+            many_to_many = []
+
+            for table in cls.metadata.tables.values():
+                lcl_m2m, rem_m2m, m2m_const = _is_many_to_many(cls, table)
+                if lcl_m2m is not None:
+                    many_to_many.append((lcl_m2m, rem_m2m, m2m_const, table))
+                elif not table.primary_key:
+                    continue
+                elif table not in table_to_map_config:
+                    mapped_cls = type(
+                        classname_for_table(cls, table.name, table),
+                        (cls, ),
+                        {"__table__": table}
+                    )
+                    map_config = _DeferredMapperConfig.config_for_cls(mapped_cls)
+                    cls.classes[map_config.cls.__name__] = mapped_cls
+                    table_to_map_config[table] = map_config
+
+            for map_config in table_to_map_config.values():
+                _relationships_for_fks(cls,
+                                       map_config,
+                                       table_to_map_config,
+                                       collection_class,
+                                       name_for_scalar_relationship,
+                                       name_for_collection_relationship,
+                                       generate_relationship)
+
+            for lcl_m2m, rem_m2m, m2m_const, table in many_to_many:
+                _m2m_relationship(cls, lcl_m2m, rem_m2m, m2m_const, table,
+                                  table_to_map_config,
+                                  collection_class,
+                                  name_for_scalar_relationship,
+                                  name_for_collection_relationship,
+                                  generate_relationship)
+
+            for map_config in _DeferredMapperConfig.classes_for_base(cls):
+                map_config.map()
+        finally:
+            _CONFIGURE_MUTEX.release()
 
     _sa_decl_prepare = True
     """Indicate that the mapping of classes should be deferred.

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

https://gerrit.sqlalchemy.org/#/q/I6d36df6639bf5cb8f137187dff68f386f5e84f88

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

Mutex on _CONFIGURE_MUTEX in automap.prepare()

Fixed a race condition which could occur if automap
:meth:.AutomapBase.prepare were used within a multi-threaded context
against other threads which may call :func:.configure_mappers as a
result of use of other mappers. The unfinished mapping work of automap
is particularly sensitive to being pulled in by a
:func:.configure_mappers step leading to errors.

Change-Id: I6d36df6639bf5cb8f137187dff68f386f5e84f88
Fixes: #4266

→ 2ac7cad

[sqlalchemy-bot]

Changes by Michael Bayer (@zzzeek):

• changed status to closed

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

Mutex on _CONFIGURE_MUTEX in automap.prepare()

Fixed a race condition which could occur if automap
:meth:.AutomapBase.prepare were used within a multi-threaded context
against other threads which may call :func:.configure_mappers as a
result of use of other mappers. The unfinished mapping work of automap
is particularly sensitive to being pulled in by a
:func:.configure_mappers step leading to errors.

Change-Id: I6d36df6639bf5cb8f137187dff68f386f5e84f88
Fixes: #4266
(cherry picked from commit 2ac7cad)

→ 553f67f