meh

betty/service.py

@@ -1,6 +1,8 @@
 """
 Provide a service container.
 """
+from __future__ import annotations
+
 from collections import defaultdict
 from collections.abc import Callable, MutableMapping, Mapping, Awaitable
 from types import TracebackType
@@ -59,6 +61,31 @@ def build(self) -> ServiceContainer:
         raise NotImplementedError
 
 
+class _CyclicDependencyGuardServiceContainer(ServiceContainer):
+    def __init__(self, decorated: ServiceContainer, root_service_id: ServiceId):
+        self._decorated = decorated
+        self._seen_service_ids = [root_service_id]
+        self._lock = AsynchronizedLock.threading()
+
+    @override
+    async def get(self, service_id: ServiceId) -> Service:
+        print('GET')
+        print(self._seen_service_ids)
+        print(service_id)
+        if service_id in self._seen_service_ids:
+            raise _CyclicDependency([*self._seen_service_ids, service_id])
+        self._seen_service_ids.append(service_id)
+        return await self._decorated.get(service_id)
+
+    @override
+    async def start(self) -> None:
+        await self._decorated.start()
+
+    @override
+    async def stop(self) -> None:
+        await self._decorated.stop()
+
+
 class _DefaultServiceContainer(ServiceContainer):
     def __init__(self, service_factories: Mapping[ServiceId, ServiceFactory]):
         self._service_factories = service_factories
@@ -86,7 +113,8 @@ async def _initialize(self, service_id: ServiceId) -> Service:
             service_factory = self._service_factories[service_id]
         except KeyError:
             raise _ServiceNotFound(f'Service "{service_id}" is unknown.')
-        return await service_factory(self)
+        initializing_service_container = _CyclicDependencyGuardServiceContainer(self, service_id)
+        return await service_factory(initializing_service_container)
 
     async def start(self) -> None:
         assert not self._started

betty/tests/test_service.py

@@ -2,7 +2,7 @@
 
 import pytest
 
-from betty.service import _DefaultServiceContainerBuilder, ServiceId, _ServiceNotFound, ServiceContainer, \
+from betty.service import _DefaultServiceContainerBuilder, _ServiceNotFound, ServiceContainer, \
     _CyclicDependency
 
 
@@ -15,13 +15,13 @@ def __init__(self, dependency: DummyService):
         pass
 
 
-class DummyLeftHandCyclingDependencyService:
-    def __init__(self, dependency: DummyRightHandCyclingDependencyService):
+class DummyLeftHandCyclicDependencyService:
+    def __init__(self, dependency: DummyRightHandCyclicDependencyService):
         pass
 
 
-class DummyRightHandCyclingDependencyService:
-    def __init__(self, dependency: DummyLeftHandCyclingDependencyService):
+class DummyRightHandCyclicDependencyService:
+    def __init__(self, dependency: DummyLeftHandCyclicDependencyService):
         pass
 
 
@@ -72,11 +72,11 @@ async def test_with_cyclic_dependency(self) -> None:
         left_hand_dependency_service_id = 'MyFirstLeftHandDependency'
         right_hand_dependency_service_id = 'MyFirstRightHandDependency'
 
-        async def _new_dummy_left_hand_dependency_service(services: ServiceContainer) -> DummyLeftHandCyclingDependencyService:
-            return DummyLeftHandCyclingDependencyService(await services.get(right_hand_dependency_service_id))
+        async def _new_dummy_left_hand_dependency_service(services: ServiceContainer) -> DummyLeftHandCyclicDependencyService:
+            return DummyLeftHandCyclicDependencyService(await services.get(right_hand_dependency_service_id))
 
-        async def _new_dummy_right_hand_dependency_service(services: ServiceContainer) -> DummyRightHandCyclingDependencyService:
-            return DummyRightHandCyclingDependencyService(await services.get(left_hand_dependency_service_id))
+        async def _new_dummy_right_hand_dependency_service(services: ServiceContainer) -> DummyRightHandCyclicDependencyService:
+            return DummyRightHandCyclicDependencyService(await services.get(left_hand_dependency_service_id))
         builder = _DefaultServiceContainerBuilder()
         builder.define(left_hand_dependency_service_id, service_factory=_new_dummy_left_hand_dependency_service)
         builder.define(right_hand_dependency_service_id, service_factory=_new_dummy_right_hand_dependency_service)