[FIXED] RuntimeError: There is no current event loop in thread 'Thread-1' , multithreading and asyncio error

Issue

I am having a thread which calls asyncio loops, however this causes the mentioned exception:

RuntimeError: There is no current event loop in thread 'Thread-1'.

This question: RuntimeError: There is no current event loop in thread in async + apscheduler came across the same problem, however they refered to a scheduler which I do not have.

My code is the following:

def worker(ws):
      l1 = asyncio.get_event_loop()
      l1.run_until_complete(ws.start())  


      l2 = asyncio.get_event_loop()
      l2.run_forever()


if __name__ == '__main__':
    ws = Server()
    p = threading.Thread(target=worker,args=(ws,))
    p.start()


    while True:
        try:
            #...do sth
        except KeyboardInterrupt:
            p.join()
            exit() 

Solution

New thread doesn't have an event loop so you have to pass and set it explicitly:

def worker(ws, loop):
    asyncio.set_event_loop(loop)
    loop.run_until_complete(ws.start())

if __name__ == '__main__':
    ws = Server()
    loop = asyncio.new_event_loop()
    p = threading.Thread(target=worker, args=(ws, loop,))
    p.start()

Also, p.join() won't terminate your script correctly as you never stop the server so your loop will continue running, presumably hanging up the thread. You should call smth like loop.call_soon_threadsafe(ws.shutdown) before joining the thread, ideally waiting for the server's graceful shutdown.

Answered By - hoefling