Implement async mode for Dependency provider

src/dependency_injector/providers.pxd

@@ -33,6 +33,7 @@ cdef class Delegate(Provider):
 
 cdef class Dependency(Provider):
     cdef object __instance_of
+    cdef bint __async
 
 
 cdef class ExternalDependency(Dependency):

src/dependency_injector/providers.pyx

@@ -452,6 +452,7 @@ cdef class Dependency(Provider):
             )
 
         self.__instance_of = instance_of
+        self.__async = False
         super(Dependency, self).__init__()
 
     def __deepcopy__(self, memo):
@@ -480,9 +481,19 @@ cdef class Dependency(Provider):
 
         instance = self.__last_overriding(*args, **kwargs)
 
-        if not isinstance(instance, self.instance_of):
-            raise Error('{0} is not an '.format(instance) +
-                        'instance of {0}'.format(self.instance_of))
+        if __isawaitable(instance):
+            future_result = asyncio.Future()
+            instance = asyncio.ensure_future(instance)
+            instance.add_done_callback(functools.partial(self._async_provide, future_result))
+            self.__async = True
+            return future_result
+
+        self._check_instance_type(instance)
+
+        if self.__async:
+            result = asyncio.Future()
+            result.set_result(instance)
+            return result
 
         return instance
 
@@ -515,6 +526,19 @@ cdef class Dependency(Provider):
         """
         return self.override(provider)
 
+    def _async_provide(self, future_result, future):
+        instance = future.result()
+        try:
+            self._check_instance_type(instance)
+        except Error as exception:
+            future_result.set_exception(exception)
+        else:
+            future_result.set_result(instance)
+
+    def _check_instance_type(self, instance):
+        if not isinstance(instance, self.instance_of):
+            raise Error('{0} is not an instance of {1}'.format(instance, self.instance_of))
+
 
 cdef class ExternalDependency(Dependency):
     """:py:class:`ExternalDependency` provider describes dependency interface.

tests/unit/providers/test_async_py36.py

@@ -1,7 +1,7 @@
 import asyncio
 import random
 
-from dependency_injector import containers, providers
+from dependency_injector import containers, providers, errors
 
 # Runtime import to get asyncutils module
 import os
@@ -459,3 +459,55 @@ class ProvidedInstanceTests(AsyncTestCase):
         self.assertIs(instance1.resource, RESOURCE1)
         self.assertIs(instance2.resource, RESOURCE1)
         self.assertIs(instance1.resource, instance2.resource)
+
+
+class DependencyTests(AsyncTestCase):
+
+    def test_isinstance(self):
+        dependency = 1.0
+
+        async def get_async():
+            return dependency
+
+        provider = providers.Dependency(instance_of=float)
+        provider.override(providers.Callable(get_async))
+
+        dependency1 = self._run(provider())
+        dependency2 = self._run(provider())
+
+        self.assertEqual(dependency1, dependency)
+        self.assertEqual(dependency2, dependency)
+
+    def test_isinstance_invalid(self):
+        async def get_async():
+            return {}
+
+        provider = providers.Dependency(instance_of=float)
+        provider.override(providers.Callable(get_async))
+
+        with self.assertRaises(errors.Error):
+            self._run(provider())
+
+    def test_async_mode(self):
+        dependency = 123
+
+        async def get_async():
+            return dependency
+
+        def get_sync():
+            return dependency
+
+        provider = providers.Dependency(instance_of=int)
+        provider.override(providers.Factory(get_async))
+
+        dependency1 = self._run(provider())
+        dependency2 = self._run(provider())
+        self.assertEqual(dependency1, dependency)
+        self.assertEqual(dependency2, dependency)
+
+        provider.override(providers.Factory(get_sync))
+
+        dependency3 = self._run(provider())
+        dependency4 = self._run(provider())
+        self.assertEqual(dependency3, dependency)
+        self.assertEqual(dependency4, dependency)