AsyncModbusTcpClient stops after ~30 seconds of inactivity

[RoxanaDaniela]

Hello,

I'm using python3-pymodbus/now 3.0.0-5 all from packages.debian.org with AsyncModbusTcpClient connected with an IP from modbus device and port=502.

I already have a asyncio running loop and what I do is client = AsyncModbusTcpClient("x.x.x.x", 502) and await client.connect() then I successfully read some registers with await client.read_input_registers but in a few seconds (30s of inactivity- without writing or reading registers), the client disconnects ['ConnectionException', 'Modbus Error: [Connection] Not connected[AsyncModbusTcpClient x.x.x.x:502]'] and client.connected returns fail.

Is there any parameter to keep alive the connection or another approach?

Thank you

[janiversen]

First of all let me warn you, the version you are using have quite a number of bugs, 3.0.2 is the stable release.

Did you read the docs ? https://pymodbus.readthedocs.io/en/v3.0.2/source/library/pymodbus.client.html#client-setup

We do not have a keep-alive option, but it might be activated pr default at socket level, I do not remember. Personally I think your problem is something else.

Pull requests are welcome.

[RoxanaDaniela]

Now I'm running with 3.0.2 and I have the same behaviour. Somehow the connection with the client closes automatically after a few seconds? It's that possible? Now I run a very simple code from the examples shown in the documentation. With 10 seconds I don't have this problem, I see the last print with End of Program.

from pymodbus.client import AsyncModbusTcpClient
def setup_async_client():
    client = AsyncModbusTcpClient("x.x.x.x", 502)
    return client

async def run_async_client(client):
    print("Connecting..")
    await client.connect()
    print("Client connected: {}".format(client.connected))

    reg = await client.read_input_registers(128, 1)
    print("Input Register is: {}".format(reg.registers))

    print("Waiting 30s..")
    await asyncio.sleep(30)
    print("End of Waiting")

    print("Client connected: {}".format(client.connected))
    reg = await client.read_input_registers(128, 1)
    print("Input Register is{}".format(reg.registers))
    print("Client protocol{}".format(client.protocol))
    print("End of Program")    

if __name__ == "__main__":
    testclient = setup_async_client()
    asyncio.run(run_async_client(testclient))

OUTPUT:
Connecting..
Client connected: True
Input Register is: [1]
Waiting 20s..
End of Waiting
Client connected: False
....
raise ConnectionException(f"Not connected[{str(self)}]")
pymodbus.exceptions.ConnectionException: Modbus Error: [Connection] Not connected[AsyncModbusTcpClient x.x.x.x:502]

[janiversen]

Please add debug as per documentation (README), otherwise I do not have a clue what happens.

Apart from the missing debug log, your example is quite nice and makes it easy to test.

[janiversen]

I just ran your example:

(pymodbus) examples % python3 connect.py
Connecting..
Client connected: True
Input Register is: [17]
Waiting 30s..
End of Waiting
Client connected: True
Input Register is[17]
Client protocolModbusClientProtocol 127.0.0.1:502
End of Program

Which makes me wonder if the problem is that your device disconnects. Most devices have a timeout builtin to break an unused connection. From my experience the timeout is normally around 20-30 seconds.

Add logging and you will most likely see a message that the device closed the connection.

The keep-alive option of tcp/ip will NOT help here, since it is on application level, the device needs a modbus request within its builtin timeout.

[RoxanaDaniela]

Thank you a lot, I will add logging to see what happens.
With version 2.5.3 and sync modbus client from pyModbusTCP.client import ModbusClient everything works fine with same device, that's why I didn't suspect that it could be a problem with device timeout. Maybe it's different with async

[janiversen]

timeout did not really work in 2.5.3 and the timing in sync was quite different.