[Python] Intermittently losing ContextVar when passing from parent to child thread

I have a subclass of Thread that I use across my project. In this class, I pass in the ContextVar manually. However, at times (once or twice a day), I notice that the ContextVar in the child thread is not set (reverted to a default value).

class MyThread(Thread):
def __init__(
self,
group: None = None,
target: Callable[..., Any] | None = None,
name: str | None = None,
args: tuple[Any, ...] = (),
kwargs: dict[str, Any] | None = None,
*,
daemon: bool | None = None,
):
super().__init__(group=group, target=target, name=name, args=args, kwargs=kwargs, daemon=daemon)
self.my_resource = get_resource_info()

def run(self):
self._exception = None
try:
set_my_resource_info(self.my_resource.name, self.my_resource.kind)
self._return_value = super().run()
except BaseException as e:
self._exception = e

def join(self, timeout: float | None = None):
super().join(timeout)
if self._exception:
raise self._exception
return self._return_value


And in another module I have:

@dataclass
class MyResourceInfo:
name: str
kind: str ="unknown"


resource_info: ContextVar[MyResourceInfo] = ContextVar(
'my_resource_info',
default=MyResourceInfo(name=get_default_resource_name()),
)

def set_resource_info(name: str, kind: str = 'unknown') -> Token[MyResourceInfo]:
return resource_info.set(MyResourceInfo(name=name, kind=kind))



Why does the context var revert to default value intermittently in child threads?

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