Feature: Context local provider (#442)

Co-authored-by: Rollo Konig Brock <rollo@b2c2.com>

Author: sonthonaxrk

src/dependency_injector/containers.c

@@ -175,6 +175,11 @@ cdef class ThreadLocalSingleton(BaseSingleton):
  cpdef object _provide(self, tuple args, dict kwargs)
 
 
+cdef class ContextLocalSingleton(BaseSingleton):
+
+ cpdef object _provide(self, tuple args, dict kwargs)
+
+
 cdef class DelegatedThreadLocalSingleton(ThreadLocalSingleton):
  pass
 

src/dependency_injector/providers.c

@@ -336,6 +336,9 @@ class DelegatedThreadSafeSingleton(ThreadSafeSingleton[T]): ...
 class ThreadLocalSingleton(BaseSingleton[T]): ...
 
 
+class ContextLocalSingleton(BaseSingleton[T]): ...
+
+
 class DelegatedThreadLocalSingleton(ThreadLocalSingleton[T]): ...
 
 

src/dependency_injector/providers.pxd

@@ -13,6 +13,12 @@ import types
 import threading
 import warnings
 
+try:
+ import contextvars
+except ImportError:
+ contextvars = None
+
+
 try:
  import asyncio
 except ImportError:
@@ -2928,6 +2934,89 @@ cdef class ThreadLocalSingleton(BaseSingleton):
  future_result.set_result(instance)
 
 
+cdef class ContextLocalSingleton(BaseSingleton):
+ """Context-local singleton provides single objects in scope of a context.
+
+ .. py:attribute:: provided_type
+
+ If provided type is defined, provider checks that providing class is
+ its subclass.
+
+ :type: type | None
+
+ .. py:attribute:: cls
+ :noindex:
+
+ Class that provides object.
+ Alias for :py:attr:`provides`.
+
+ :type: type
+ """
+ _none = object()
+
+ def __init__(self, provides=None, *args, **kwargs):
+ """Initializer.
+
+ :param provides: Provided type.
+ :type provides: type
+ """
+ if not contextvars:
+ raise RuntimeError(
+ 'Contextvars library not found. This provider '
+ 'requires Python 3.7 or a backport of contextvars. '
+ 'To install a backport run "pip install contextvars".'
+ )
+
+ super(ContextLocalSingleton, self).__init__(provides, *args, **kwargs)
+ self.__storage = contextvars.ContextVar('__storage', default=self._none)
+
+ def reset(self):
+ """Reset cached instance, if any.
+
+ :rtype: None
+ """
+ instance = self.__storage.get()
+ if instance is self._none:
+ return SingletonResetContext(self)
+
+ if __is_future_or_coroutine(instance):
+ asyncio.ensure_future(instance).cancel()
+
+ self.__storage.set(self._none)
+
+ return SingletonResetContext(self)
+
+ cpdef object _provide(self, tuple args, dict kwargs):
+ """Return single instance."""
+ cdef object instance
+
+ instance = self.__storage.get()
+
+ if instance is self._none:
+ instance = __factory_call(self.__instantiator, args, kwargs)
+
+ if __is_future_or_coroutine(instance):
+ future_result = asyncio.Future()
+ instance = asyncio.ensure_future(instance)
+ instance.add_done_callback(functools.partial(self._async_init_instance, future_result))
+ self.__storage.set(future_result)
+ return future_result
+
+ self.__storage.set(instance)
+
+ return instance
+
+ def _async_init_instance(self, future_result, result):
+ try:
+ instance = result.result()
+ except Exception as exception:
+ self.__storage.set(self._none)
+ future_result.set_exception(exception)
+ else:
+ self.__storage.set(instance)
+ future_result.set_result(instance)
+
+
 cdef class DelegatedThreadLocalSingleton(ThreadLocalSingleton):
  """Delegated thread-local singleton is injected "as is".
 
@@ -4645,4 +4734,4 @@ cpdef str _class_qualname(object instance):
  name = getattr(instance.__class__, '__qualname__', None)
  if not name:
  name = '.'.join((instance.__class__.__module__, instance.__class__.__name__))
- return name
+ return name