ThreadSafeSingleton provides None if called from separate thread while an earlier call is still processing. #433
Description
Hello, 4.6.0 seems to have created an issue with providers.ThreadSafeSingleton.
If the singleton object to be created has a lengthy init time, and the provider is called a second time while the first one is still being created from a seperate thread, the second call returns None instead of the object.
You can recreate this issue with the example below.
import threading
import unittest
from dependency_injector import providers
class ThingThatTakesLongTimeToInitAndNeedsToBeSingleton:
def __init__(self):
self.j = 0
for i in range(1000000):
self.j += i
provider_of_annoying_object = providers.ThreadSafeSingleton(
ThingThatTakesLongTimeToInitAndNeedsToBeSingleton
)
class WorkerThatCanMoveToThreadAndCallProvider:
def __init__(self, provider):
super().__init__()
self._provider = provider
self.thing_i_made = 0
def use_provider(self):
self.thing_i_made = self._provider()
# Interestingly, if you add a print statement here, it prints 3 times, not twice.
class TestProvidersInThreads(unittest.TestCase):
def test_provider_called_in_thread(self):
worker_1 = WorkerThatCanMoveToThreadAndCallProvider(provider_of_annoying_object)
thread_1 = threading.Thread(target=worker_1.use_provider)
worker_2 = WorkerThatCanMoveToThreadAndCallProvider(provider_of_annoying_object)
thread_2 = threading.Thread(target=worker_2.use_provider)
thread_1.start()
thread_2.start()
thread_1.join()
thread_2.join()
self.assertIsInstance(worker_1.thing_i_made, ThingThatTakesLongTimeToInitAndNeedsToBeSingleton)
self.assertIsInstance(worker_2.thing_i_made, ThingThatTakesLongTimeToInitAndNeedsToBeSingleton)
self.assertIs(worker_1.thing_i_made, worker_2.thing_i_made)
For versions > 4.6.0, this test fails with:
self.assertIsInstance(worker_2.thing_i_made, ThingThatTakesLongTimeToInitAndNeedsToBeSingleton)
AssertionError: None is not an instance of <class 'tests.providers.test_why_image_interface_dead.ThingThatTakesLongTimeToInitAndNeedsToBeSingleton'>