CODEWITHSUNDEEP
pythonpython-3.5python-multithreadingpython-asyncio
Sergio Ivanuzzo
Sergio Ivanuzzo

Reputation: 1922

Python3 asyncio - running two servers in own thread

I have my servers classes inherited from BaseServer:

class BaseServer(object):

    def __init__(self, host, port):
        self.loop = asyncio.new_event_loop()
        asyncio.set_event_loop(self.loop)

        self.instance = asyncio.start_server(self.handle_connection, host = host, port = port)

    async def handle_connection(self, reader: StreamReader, writer: StreamWriter):
        pass

    def start(self):
        # wrapping coroutine into ensure_future to allow it to call from call_soon
        # wrapping into lambda to make it callable
        callback = asyncio.ensure_future(self.instance)
        self.loop.call_soon(lambda: callback)
        self.loop.run_forever()
        self.loop.close()

    def stop(self):
        self.loop.call_soon_threadsafe(self.loop.stop)

    @staticmethod
    def get_instance():
        return BaseServer(None, None)

I need two servers running in own thread to processing requests in parallel. But when I trying to run them as needed, only first server is running. Below how I run them:

if __name__ == '__main__':
    loop = asyncio.new_event_loop()
    asyncio.set_event_loop(loop)

    async def run():
        pool = ThreadPoolExecutor(max_workers=cpu_count())

        await loop.run_in_executor(pool, Server1.get_instance().start)
        await loop.run_in_executor(pool, Server2.get_instance().start)

    loop.run_until_complete(run())
  1. What am I doing wrong? How to run each server in own thread?
  2. When asyncio.set_event_loop is calling from def __init__ I got next error:

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

But if I remove asyncio.set_event_loop from def __init__ and move it to def start error disappears. Why this happened?

Upvotes: 2

Views: 3587

Answers (1)

Vincent
Vincent

Reputation: 13415

Following up on OP's comment:

But running two servers via run_until_complete in the same loop blocks loop for one of servers to process request to another, isn't it ? How to run two servers correctly ?

Here is a modified version of the TCP server example from the asyncio documentation for python 3.5:

# Start server 1
coro1 = asyncio.start_server(handle_echo, '127.0.0.1', 8888, loop=loop)
server1 = loop.run_until_complete(coro1)
print('Serving 1 on {}'.format(server1.sockets[0].getsockname()))

# Start server 2
coro2 = asyncio.start_server(handle_echo, '127.0.0.1', 8889, loop=loop)
server2 = loop.run_until_complete(coro2)
print('Serving 2 on {}'.format(server2.sockets[0].getsockname()))

# Serve requests until Ctrl+C is pressed
try:
    loop.run_forever()
except KeyboardInterrupt:
    pass

# Close the servers
server1.close()
loop.run_until_complete(server1.wait_closed())
server2.close()
loop.run_until_complete(server2.wait_closed())

# Close the loop
loop.close()

Note that with python 3.7 additions to asyncio, it would look much nicer:

async def main():
    server1 = await asyncio.start_server(
        handle_echo, '127.0.0.1', 8888)

    addr1 = server1.sockets[0].getsockname()
    print(f'Serving 1 on {addr1}')

    server2 = await asyncio.start_server(
        handle_echo, '127.0.0.1', 8889)

    addr2 = server2.sockets[0].getsockname()
    print(f'Serving 2 on {addr2}')

    async with server1, server2:
        await asyncio.gather(
            server1.serve_forever(), server2.serve_forever())

asyncio.run(main())

Upvotes: 5

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