1 files changed, 89 insertions, 0 deletions
diff --git a/lib/sqlalchemy/ext/asyncio/base.py b/lib/sqlalchemy/ext/asyncio/base.py
new file mode 100644
index 0000000..3f77f55
--- /dev/null
+++ b/lib/sqlalchemy/ext/asyncio/base.py
@@ -0,0 +1,89 @@
+import abc
+import functools
+import weakref
+
+from . import exc as async_exc
+
+
+class ReversibleProxy:
+    # weakref.ref(async proxy object) -> weakref.ref(sync proxied object)
+    _proxy_objects = {}
+    __slots__ = ("__weakref__",)
+
+    def _assign_proxied(self, target):
+        if target is not None:
+            target_ref = weakref.ref(target, ReversibleProxy._target_gced)
+            proxy_ref = weakref.ref(
+                self,
+                functools.partial(ReversibleProxy._target_gced, target_ref),
+            )
+            ReversibleProxy._proxy_objects[target_ref] = proxy_ref
+
+        return target
+
+    @classmethod
+    def _target_gced(cls, ref, proxy_ref=None):
+        cls._proxy_objects.pop(ref, None)
+
+    @classmethod
+    def _regenerate_proxy_for_target(cls, target):
+        raise NotImplementedError()
+
+    @classmethod
+    def _retrieve_proxy_for_target(cls, target, regenerate=True):
+        try:
+            proxy_ref = cls._proxy_objects[weakref.ref(target)]
+        except KeyError:
+            pass
+        else:
+            proxy = proxy_ref()
+            if proxy is not None:
+                return proxy
+
+        if regenerate:
+            return cls._regenerate_proxy_for_target(target)
+        else:
+            return None
+
+
+class StartableContext(abc.ABC):
+    __slots__ = ()
+
+    @abc.abstractmethod
+    async def start(self, is_ctxmanager=False):
+        pass
+
+    def __await__(self):
+        return self.start().__await__()
+
+    async def __aenter__(self):
+        return await self.start(is_ctxmanager=True)
+
+    @abc.abstractmethod
+    async def __aexit__(self, type_, value, traceback):
+        pass
+
+    def _raise_for_not_started(self):
+        raise async_exc.AsyncContextNotStarted(
+            "%s context has not been started and object has not been awaited."
+            % (self.__class__.__name__)
+        )
+
+
+class ProxyComparable(ReversibleProxy):
+    __slots__ = ()
+
+    def __hash__(self):
+        return id(self)
+
+    def __eq__(self, other):
+        return (
+            isinstance(other, self.__class__)
+            and self._proxied == other._proxied
+        )
+
+    def __ne__(self, other):
+        return (
+            not isinstance(other, self.__class__)
+            or self._proxied != other._proxied
+        )