[pygobject/wip/type-object-concurrency-fix] IntrospectionModule: handle two threads loading type at same time

[Ray Strode <halfline src gnome org>]

commit eb791e7cca0998bc75e0b3f7e8ecf2672c96d7f8
Author: Ray Strode <rstrode redhat com>
Date:   Wed Jun 10 18:04:07 2020 -0400

    IntrospectionModule: handle two threads loading type at same time
    
    If two threads are trying to load a type at exactly the same time,
    it's possible for two wrappers to get generated for the type.
    One thread will end up with the wrapper that's not blessed as the
    "real" one and future calls will fail.  The blessed wrapper will
    be incomplete, and so future calls from it will fail as well.
    
    This commit adds a lock to ensure the two threads don't stomp
    on each others toes.

 gi/module.py | 110 +++++++++++++++++++++++++++++++----------------------------
 1 file changed, 58 insertions(+), 52 deletions(-)
---
diff --git a/gi/module.py b/gi/module.py
index f9e26bc2..93b8e6a3 100644
--- a/gi/module.py
+++ b/gi/module.py
@@ -21,6 +21,7 @@
 # USA
 
 import importlib
+from threading import Lock
 
 import gi
 
@@ -117,6 +118,8 @@ class IntrospectionModule(object):
         if self._version is None:
             self._version = repository.get_version(self._namespace)
 
+        self._lock = Lock()
+
     def __getattr__(self, name):
         info = repository.find_by_name(self._namespace, name)
         if not info:
@@ -125,39 +128,41 @@ class IntrospectionModule(object):
 
         if isinstance(info, EnumInfo):
             g_type = info.get_g_type()
-            wrapper = g_type.pytype
 
-            if wrapper is None:
-                if info.is_flags():
-                    if g_type.is_a(TYPE_FLAGS):
-                        wrapper = flags_add(g_type)
-                    else:
-                        assert g_type == TYPE_NONE
-                        wrapper = flags_register_new_gtype_and_add(info)
-                else:
-                    if g_type.is_a(TYPE_ENUM):
-                        wrapper = enum_add(g_type)
+            with self._lock:
+                wrapper = g_type.pytype
+
+                if wrapper is None:
+                    if info.is_flags():
+                        if g_type.is_a(TYPE_FLAGS):
+                            wrapper = flags_add(g_type)
+                        else:
+                            assert g_type == TYPE_NONE
+                            wrapper = flags_register_new_gtype_and_add(info)
                     else:
-                        assert g_type == TYPE_NONE
-                        wrapper = enum_register_new_gtype_and_add(info)
-
-                wrapper.__info__ = info
-                wrapper.__module__ = 'gi.repository.' + info.get_namespace()
-
-                # Don't use upper() here to avoid locale specific
-                # identifier conversion (e. g. in Turkish 'i'.upper() == 'i')
-                # see https://bugzilla.gnome.org/show_bug.cgi?id=649165
-                ascii_upper_trans = ''.maketrans(
-                    'abcdefgjhijklmnopqrstuvwxyz',
-                    'ABCDEFGJHIJKLMNOPQRSTUVWXYZ')
-                for value_info in info.get_values():
-                    value_name = value_info.get_name_unescaped().translate(ascii_upper_trans)
-                    setattr(wrapper, value_name, wrapper(value_info.get_value()))
-                for method_info in info.get_methods():
-                    setattr(wrapper, method_info.__name__, method_info)
-
-            if g_type != TYPE_NONE:
-                g_type.pytype = wrapper
+                        if g_type.is_a(TYPE_ENUM):
+                            wrapper = enum_add(g_type)
+                        else:
+                            assert g_type == TYPE_NONE
+                            wrapper = enum_register_new_gtype_and_add(info)
+
+                    wrapper.__info__ = info
+                    wrapper.__module__ = 'gi.repository.' + info.get_namespace()
+
+                    # Don't use upper() here to avoid locale specific
+                    # identifier conversion (e. g. in Turkish 'i'.upper() == 'i')
+                    # see https://bugzilla.gnome.org/show_bug.cgi?id=649165
+                    ascii_upper_trans = ''.maketrans(
+                        'abcdefgjhijklmnopqrstuvwxyz',
+                        'ABCDEFGJHIJKLMNOPQRSTUVWXYZ')
+                    for value_info in info.get_values():
+                        value_name = value_info.get_name_unescaped().translate(ascii_upper_trans)
+                        setattr(wrapper, value_name, wrapper(value_info.get_value()))
+                    for method_info in info.get_methods():
+                        setattr(wrapper, method_info.__name__, method_info)
+
+                if g_type != TYPE_NONE:
+                    g_type.pytype = wrapper
 
         elif isinstance(info, RegisteredTypeInfo):
             g_type = info.get_g_type()
@@ -188,27 +193,28 @@ class IntrospectionModule(object):
             else:
                 raise NotImplementedError(info)
 
-            # Check if there is already a Python wrapper that is not a parent class
-            # of the wrapper being created. If it is a parent, it is ok to clobber
-            # g_type.pytype with a new child class wrapper of the existing parent.
-            # Note that the return here never occurs under normal circumstances due
-            # to caching on the __dict__ itself.
-            if g_type != TYPE_NONE:
-                type_ = g_type.pytype
-                if type_ is not None and type_ not in bases:
-                    self.__dict__[name] = type_
-                    return type_
-
-            dict_ = {
-                '__info__': info,
-                '__module__': 'gi.repository.' + self._namespace,
-                '__gtype__': g_type
-            }
-            wrapper = metaclass(name, bases, dict_)
-
-            # Register the new Python wrapper.
-            if g_type != TYPE_NONE:
-                g_type.pytype = wrapper
+            with self._lock:
+                # Check if there is already a Python wrapper that is not a parent class
+                # of the wrapper being created. If it is a parent, it is ok to clobber
+                # g_type.pytype with a new child class wrapper of the existing parent.
+                # Note that the return here never occurs under normal circumstances due
+                # to caching on the __dict__ itself.
+                if g_type != TYPE_NONE:
+                    type_ = g_type.pytype
+                    if type_ is not None and type_ not in bases:
+                        self.__dict__[name] = type_
+                        return type_
+
+                dict_ = {
+                    '__info__': info,
+                    '__module__': 'gi.repository.' + self._namespace,
+                    '__gtype__': g_type
+                }
+                wrapper = metaclass(name, bases, dict_)
+
+                # Register the new Python wrapper.
+                if g_type != TYPE_NONE:
+                    g_type.pytype = wrapper
 
         elif isinstance(info, FunctionInfo):
             wrapper = info