You MUST await a future returned from `loop.run_in_executor()` to avoid the leak. Yuri, what should we do with the issue? I see the second similar report in the last half of the year. Sure, we can add weakrefs somewhere in futures._chain_future() but I pretty sure that the proper fix is just enforcing `await` here, e.g. 1. rename existing run_in_executor() into a private _run_in_executor() function. 2. write async trampoline: async def run_in_executor(self, executor, func, *args): return await self._run_in_executor(executor, func, *args)