Why does an async Python endpoint freeze other requests during file processing?

Declaring a function async does not make its synchronous work nonblocking. CPU loops or blocking library calls still occupy the event-loop thread. For blocking I/O, consider await asyncio.to_thread(blocking_call); for substantial CPU work, use a suitable process or worker architecture. Test by running a periodic heartbeat alongside the operation and measuring missed ticks. Do not assume threads accelerate ordinary Python CPU loops under every interpreter configuration. Bound concurrent jobs so a busy endpoint cannot create unlimited workers. Cancellation of the awaiting coroutine does not forcibly stop an already running thread, so the underlying operation still needs its own timeout or cooperative stop mechanism.