[Components] In some rare cases the method component.stop() can work incorrectly

[drew2a]

During the refactoring (#6335), we found the following potential problem:

In some rare cases the method component.stop() may not work correctly.

The current implementation (simplified) is the following:

class Session:
    async def start(self, failfast=True):
        coros = [comp.start() for comp in self.components.values()]
        await gather(*coros, return_exceptions=not failfast)

    async def shutdown(self):
        await gather(*[create_task(component.stop()) for component in self.components.values()])

That means whatever comp.start() was failed or succeeded, the corresponding component.stop() will be called during a shutdown.

That means component.stop() should distinguish initialized and uninitialized fields of the corresponding class (this is not currently being done).

[Solomon1732]

What is the way to check for a successfully started component? I'm guessing comp.started.is_set()?

[kozlovsky]

@Solomon1732 yes, but in 2730ab8 it was renamed to comp.started_event.is_set() to avoid possible mistake with a Boolean flag:

if comp.started:   # will evaluate to True even if component has not started yet 
    ...

Now it should look clearer:

if comp.started_event.is_set():
    ...