Start and stop server from v2.5.3 to v3.0.0

[e-aurelien-laporte]

Hello everyone !

I have an application using v2.5.3 which spawns multiple SlaveModbus.

These slaves contains either a ModbusTcpServer or a ModbusSerialServer which can be started or stopped via public methods. When started, the server are ran in the background via a thread.

The implementation is really simple and look like this.

from threading import Thread
from typing import Any


class ModbusServerManager:
    """Manages the Modbus server lifecycle."""

    def __init__(self, server: Any) -> None:
        self._server = server
        self._thread_server = Thread(
            target=self._server.serve_forever,
        )

    def start(self) -> None:
        self._thread_server.start()

    def stop(self) -> None:
        if self._thread_server.is_alive():
            self._server.shutdown()
            self._thread_server.join()

I have to update to version v3.0.0 because I need to use the package python3-modbus from debian 12.

I've spent multiple days trying to adapt this code using the new async pattern you adopted from this version, without any success.

I've looked for your examples, your unit tests, the documentation of asyncio, but I don't manage to make it work.

Should I use some tasks, keep using a thread, use await directly? I'm a bit lost to be honest 😕...

Note that I want the modification to be minimal and not use async functions since my whole code is complety synchronous.

I hope you'll be able to help me !

Thank in advance

[janiversen]

First of all 3.0.0 is very old and should not be used. Current version is 3.8.4

Secondly have a look at our examples, you can ether use startserver or continue use modbusserver which e.g. have a serve_forever public method. However please be aware that the 3.x server code is async.

[e-aurelien-laporte]

Hello!

First of all 3.0.0 is very old and should not be used.

I know it is not recommended to use old version of a software (people do it every day with mine 😄)...

However, as I said, this is the version provided by this package which package the version v3.0.0rc1 of your software (see here).

I don't have other choice to use this version.

Secondly have a look at our examples

I know functions StartServerXXX exist (once again, I've checked the examples and the unit tests), but I couldn't find examples where your server are ran in a program in background. That's what I'm trying to do.

I just needed some help about using asyncio to adapt this single code and have a guideline to move from v2.5.3 to an older version.

[janiversen]

Please also be aware this is the pymodbus project, NOT python3-modbus !

We have all source available on github, including unit test etc, I have no idea about the project you want to use.

[e-aurelien-laporte]

See this comment here #2541 (reply in thread).

python3-modbus provides a version of pymodbus in a debian package. I can't use pip for multiple reasons and I'm stuck using this version.

[janiversen]

It is of course up to you, which package you want to use, but it must be considered quite unusual that the maintainers of Debian include a release candidate instead of the proper release.

You might not be able to use pip in the standard environment, but you can create a virtual environment and in that install the packages you want (you can even install different python versions). I do that on my raspberry PIs, exactly to get around the Debian limitations.

Running the server in background is not a feature of pymodbus, but at a standard python functionality. We show how to use pymodbus not python :-)

If you want to you can simply run start server in background, with the method of your preference, pymodbus do not care. And just for reference a lot of our unit test run the server in background (of course using asyncio).

Please be aware that especially the release candidate had some severe bugs, which we will not be able to help you with.

[alexrudd2]

Neither Jan nor anyone else on this project have involvement with Debian's packaging of pymodbus, so you'd have to reach out to that maintainer directly.
https://tracker.debian.org/pkg/pymodbus has all the information.

I note that 3.6.9-1 is available in testing (currently trixie), so if you're able to use that package or repository I'd recommend using that.