Wrong order of callbacks

Hello,

NATS documentation says, that messages from one publisher are received in the same order as they were published. But if we make few subscriptions, and publish messages for each one few times, callbacks will be called in different order. This is because each subscriber has own message queue. Here is example:

receive.py

import asyncio
from nats.aio.client import Client as NATS

async def run(loop):

    await nc.connect("nats://nats:4222", loop=loop)

    async def message_handler_A(msg):
        print('message_handler_A')

    async def message_handler_B(msg):
        print('message_handler_B')

    async def message_handler_C(msg):
        print('message_handler_C')

    await nc.subscribe("message_handler_A", cb=message_handler_A)
    await nc.subscribe("message_handler_B", cb=message_handler_B)
    await nc.subscribe("message_handler_C", cb=message_handler_C)
    print('receiving')


if __name__ == '__main__':
    nc = NATS()
    loop = asyncio.get_event_loop()
    loop.run_until_complete(run(loop))
    loop.run_forever()

publish.py:

import asyncio
from nats.aio.client import Client as NATS

async def run(loop):
    await nc.connect("nats://nats:4222", loop=loop)
    for i in range(10):
      await nc.publish("message_handler_B", b"")
      await nc.publish("message_handler_C", b"")
      await nc.publish("message_handler_A", b"")

if __name__ == '__main__':
    nc = NATS()
    loop = asyncio.get_event_loop()
    loop.run_until_complete(run(loop))
    loop.run_forever()

Just run publish.py after receive.py.

[nxsofsys]

I’ve found that asyncio.Lock doing job. I added lock around callbacks which should run in ordered way.

[wallyqs]

Closing as that is how the client is intended to work right now (similar behavior as in the Go client).