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Setting reconnect_delay=0 in AsyncModbusTcpClient causes infinite busy-loops on connection loss #1794

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sthelen-enqs opened this issue Oct 6, 2023 · 5 comments · Fixed by #1795
Closed

Setting reconnect_delay=0 in AsyncModbusTcpClient causes infinite busy-loops on connection loss #1794

sthelen-enqs opened this issue Oct 6, 2023 · 5 comments · Fixed by #1795

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@sthelen-enqs
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Versions

  • Python: 3.11.4
  • OS: Ubuntu 20.04
  • Pymodbus: 3.5.2
  • Modbus Hardware (if used): N/A

Pymodbus Specific

  • Server: tcp - async
  • Client: tcp - async

Description

I tried setting reconnect_delay=0 in the constructor for AsyncModbusTcpClient as documented in https://pymodbus.readthedocs.io/en/latest/source/client.html#pymodbus.client.ModbusBaseClient to prevent the client from reconnecting if the TCP connection drops, but whenever the connection dropped pymodbus would instead busy-loop at 100%CPU forever.

Code and Logs

Minimal Example:

import asyncio

import pymodbus
from pymodbus.client import AsyncModbusTcpClient

pymodbus.pymodbus_apply_logging_config()


async def main():
    client = AsyncModbusTcpClient(host="127.0.0.1", port=5502, reconnect_delay=0)
    r = await client.connect()

    while True:
        if not client.reconnect_task:
            resp = await client.read_input_registers(13, 2, slave=1)
        await asyncio.sleep(5)


if __name__ == "__main__":
    asyncio.run(main())

Logs (repeat ad-infimum):

2023-10-06 17:00:22,639 DEBUG logging:102 Connecting to 127.0.0.1:5502.
2023-10-06 17:00:22,639 DEBUG logging:102 Connecting comm
2023-10-06 17:00:22,640 DEBUG logging:102 Connected to comm
2023-10-06 17:00:22,640 DEBUG logging:102 callback_connected called
2023-10-06 17:00:22,640 DEBUG logging:102 send: 0x0 0x1 0x0 0x0 0x0 0x6 0x1 0x4 0x0 0xd 0x0 0x2
2023-10-06 17:00:22,640 DEBUG logging:102 Adding transaction 1
2023-10-06 17:00:22,640 DEBUG logging:102 recv: 0x0 0x1 0x0 0x0 0x0 0x7 0x1 0x4 0x4 0x0 0xe 0x0 0xf old_data:  addr=None
2023-10-06 17:00:22,640 DEBUG logging:102 Processing: 0x0 0x1 0x0 0x0 0x0 0x7 0x1 0x4 0x4 0x0 0xe 0x0 0xf
2023-10-06 17:00:22,641 DEBUG logging:102 Factory Response[ReadInputRegistersResponse': 4]
2023-10-06 17:00:22,641 DEBUG logging:102 Getting transaction 1
2023-10-06 17:00:27,646 DEBUG logging:102 send: 0x0 0x2 0x0 0x0 0x0 0x6 0x1 0x4 0x0 0xd 0x0 0x2
2023-10-06 17:00:27,647 DEBUG logging:102 Adding transaction 2
2023-10-06 17:00:27,647 DEBUG logging:102 recv: 0x0 0x2 0x0 0x0 0x0 0x7 0x1 0x4 0x4 0x0 0xe 0x0 0xf old_data:  addr=None
2023-10-06 17:00:27,647 DEBUG logging:102 Processing: 0x0 0x2 0x0 0x0 0x0 0x7 0x1 0x4 0x4 0x0 0xe 0x0 0xf
2023-10-06 17:00:27,648 DEBUG logging:102 Factory Response[ReadInputRegistersResponse': 4]
2023-10-06 17:00:27,648 DEBUG logging:102 Getting transaction 2
2023-10-06 17:00:28,814 DEBUG logging:102 -> transport: received eof
2023-10-06 17:00:28,815 DEBUG logging:102 Connection lost comm due to None
2023-10-06 17:00:28,815 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,815 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,816 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,816 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,816 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,817 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,817 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,817 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,818 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,818 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,818 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,819 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,819 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,819 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,820 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,820 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,820 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,821 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,821 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,821 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,822 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,823 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,823 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,823 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,823 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,824 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,824 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,824 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,824 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,825 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,825 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,825 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,826 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,826 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,826 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,826 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,826 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,826 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,827 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,827 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,827 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,827 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,827 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,827 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,828 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,828 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,828 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,828 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,828 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,828 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,828 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,828 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,828 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,829 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,829 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,829 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,829 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,829 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,829 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,830 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,830 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,830 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,830 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,830 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,830 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,830 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)
2023-10-06 17:00:28,830 DEBUG logging:102 Wait comm 0 ms before reconnecting.
2023-10-06 17:00:28,831 DEBUG logging:102 Connecting comm
2023-10-06 17:00:28,831 WARNING logging:108 Failed to connect [Errno 111] Connect call failed ('127.0.0.1', 5502)

For the server I used the following code and then just killed it with ^C after the first few successful reads:

import asyncio

from pymodbus.datastore import (
    ModbusSequentialDataBlock,
    ModbusServerContext,
    ModbusSlaveContext,
)
from pymodbus.server import StartAsyncTcpServer

datablock = ModbusSequentialDataBlock(0, list(range(25)))

ctx = ModbusServerContext(
    slaves=ModbusSlaveContext(di=datablock, co=datablock, hr=datablock, ir=datablock),
    single=True,
)

asyncio.run(
    StartAsyncTcpServer(
        context=ctx, address=("127.0.0.1", 5502), ignore_missing_slaves=True
    )
)
@sthelen-enqs sthelen-enqs changed the title Setting reconnect_delay=0 in AsyncModbusTcpClient constructor causes infinite busy-loops on connection loss Setting reconnect_delay=0 in AsyncModbusTcpClient causes infinite busy-loops on connection loss Oct 6, 2023
@janiversen
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Sounds like you have found a bug, thanks for reporting it.

I have enough information to debug and hopefully find/repair the problem.

@janiversen
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Please give your program a go, with this patch installed:

#1795

It should work, but I do not have time to test it thoroughly right now.

@janiversen janiversen mentioned this issue Oct 6, 2023
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@janiversen
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Sorry I was too fast, this broke something. I will make a new version tomorrow.

@janiversen
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If you want to test use #1795

It will be part of either 3.5.3 or 3.6.0, but there are no confirmed time at this moment.

@sthelen-enqs
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Thanks for the quick fix, seems to look good so far in tests.

@github-actions github-actions bot locked as resolved and limited conversation to collaborators Oct 20, 2023
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Reconect_delay == 0, do not reconnect. pymodbus-dev/pymodbus
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@janiversen @sthelen-enqs