Add singleton implementation + tests for all singleton types

src/dependency_injector/providers.pxd

@@ -141,6 +141,7 @@ cdef class FactoryAggregate(Provider):
 # Singleton providers
 cdef class BaseSingleton(Provider):
     cdef Factory __instantiator
+    cdef bint __async
 
 
 cdef class Singleton(BaseSingleton):

src/dependency_injector/providers.pyx

@@ -1941,6 +1941,7 @@ cdef class BaseSingleton(Provider):
                 self.__class__, self.__class__.provided_type))
 
         self.__instantiator = Factory(provides, *args, **kwargs)
+        self.__async = False
 
         super(BaseSingleton, self).__init__()
 
@@ -2128,10 +2129,30 @@ cdef class Singleton(BaseSingleton):
     cpdef object _provide(self, tuple args, dict kwargs):
         """Return single instance."""
         if self.__storage is None:
-            self.__storage = __factory_call(self.__instantiator,
-                                            args, kwargs)
+            instance = __factory_call(self.__instantiator, args, kwargs)
+
+            if __isawaitable(instance):
+                future_result = asyncio.Future()
+                instance = asyncio.ensure_future(instance)
+                instance.add_done_callback(functools.partial(self._async_init_instance, future_result))
+                self.__storage = future_result
+                return future_result
+
+            self.__storage = instance
+
+        if self.__async:
+            result = asyncio.Future()
+            result.set_result(self.__storage)
+            return result
+
         return self.__storage
 
+    def _async_init_instance(self, future_result, result):
+        instance = result.result()
+        self.__storage = instance
+        self.__async = True
+        future_result.set_result(instance)
+
 
 cdef class DelegatedSingleton(Singleton):
     """Delegated singleton is injected "as is".
@@ -3488,8 +3509,20 @@ def merge_dicts(dict1, dict2):
     return result
 
 
+def isawaitable(obj):
+    """Check if object is a coroutine function.
+
+    Return False for any object in Python 3.4 or below.
+    """
+    try:
+        return inspect.isawaitable(obj)
+    except AttributeError:
+        return False
+
+
 def iscoroutinefunction(obj):
     """Check if object is a coroutine function.
+
     Return False for any object in Python 3.4 or below.
     """
     try:
@@ -3500,6 +3533,7 @@ def iscoroutinefunction(obj):
 
 def isasyncgenfunction(obj):
     """Check if object is an asynchronous generator function.
+
     Return False for any object in Python 3.4 or below.
     """
     try:

tests/unit/providers/test_async_py36.py

@@ -218,3 +218,154 @@ class FactoryTests(AsyncTestCase):
         self.assertIs(service2.client.resource2, RESOURCE2)
 
         self.assertIsNot(service1.client, service2.client)
+
+
+class SingletonTests(AsyncTestCase):
+
+    def test_injections(self):
+        class ContainerWithSingletons(containers.DeclarativeContainer):
+            resource1 = providers.Resource(init_resource, providers.Object(RESOURCE1))
+            resource2 = providers.Resource(init_resource, providers.Object(RESOURCE2))
+
+            client = providers.Singleton(
+                Client,
+                resource1=resource1,
+                resource2=resource2,
+            )
+
+            service = providers.Singleton(
+                Service,
+                client=client,
+            )
+
+        container = ContainerWithSingletons()
+
+        client1 = self._run(container.client())
+        client2 = self._run(container.client())
+
+        self.assertIsInstance(client1, Client)
+        self.assertIs(client1.resource1, RESOURCE1)
+        self.assertIs(client1.resource2, RESOURCE2)
+
+        self.assertIsInstance(client2, Client)
+        self.assertIs(client2.resource1, RESOURCE1)
+        self.assertIs(client2.resource2, RESOURCE2)
+
+        service1 = self._run(container.service())
+        service2 = self._run(container.service())
+
+        self.assertIsInstance(service1, Service)
+        self.assertIsInstance(service1.client, Client)
+        self.assertIs(service1.client.resource1, RESOURCE1)
+        self.assertIs(service1.client.resource2, RESOURCE2)
+
+        self.assertIsInstance(service2, Service)
+        self.assertIsInstance(service2.client, Client)
+        self.assertIs(service2.client.resource1, RESOURCE1)
+        self.assertIs(service2.client.resource2, RESOURCE2)
+
+        self.assertIs(service1, service2)
+        self.assertIs(service1.client, service2.client)
+        self.assertIs(service1.client, client1)
+
+        self.assertIs(service2.client, client2)
+        self.assertIs(client1, client2)
+
+    def test_async_mode(self):
+        instance = object()
+
+        async def create_instance():
+            return instance
+
+        provider = providers.Singleton(create_instance)
+
+        instance1 = self._run(provider())
+        instance2 = self._run(provider())
+
+        self.assertIs(instance1, instance2)
+        self.assertIs(instance, instance)
+
+
+class DelegatedSingletonTests(AsyncTestCase):
+
+    def test_async_mode(self):
+        instance = object()
+
+        async def create_instance():
+            return instance
+
+        provider = providers.DelegatedSingleton(create_instance)
+
+        instance1 = self._run(provider())
+        instance2 = self._run(provider())
+
+        self.assertIs(instance1, instance2)
+        self.assertIs(instance, instance)
+
+
+class ThreadSafeSingletonTests(AsyncTestCase):
+
+    def test_async_mode(self):
+        instance = object()
+
+        async def create_instance():
+            return instance
+
+        provider = providers.ThreadSafeSingleton(create_instance)
+
+        instance1 = self._run(provider())
+        instance2 = self._run(provider())
+
+        self.assertIs(instance1, instance2)
+        self.assertIs(instance, instance)
+
+
+class DelegatedThreadSafeSingletonTests(AsyncTestCase):
+
+    def test_async_mode(self):
+        instance = object()
+
+        async def create_instance():
+            return instance
+
+        provider = providers.DelegatedThreadSafeSingleton(create_instance)
+
+        instance1 = self._run(provider())
+        instance2 = self._run(provider())
+
+        self.assertIs(instance1, instance2)
+        self.assertIs(instance, instance)
+
+
+class ThreadLocalSingletonTests(AsyncTestCase):
+
+    def test_async_mode(self):
+        instance = object()
+
+        async def create_instance():
+            return instance
+
+        provider = providers.ThreadLocalSingleton(create_instance)
+
+        instance1 = self._run(provider())
+        instance2 = self._run(provider())
+
+        self.assertIs(instance1, instance2)
+        self.assertIs(instance, instance)
+
+
+class DelegatedThreadLocalSingletonTests(AsyncTestCase):
+
+    def test_async_mode(self):
+        instance = object()
+
+        async def create_instance():
+            return instance
+
+        provider = providers.DelegatedThreadLocalSingleton(create_instance)
+
+        instance1 = self._run(provider())
+        instance2 = self._run(provider())
+
+        self.assertIs(instance1, instance2)
+        self.assertIs(instance, instance)