How to do reconnection logic?

[SoldierStone]

After a long time disconnect with PLC, the python program in ubuntu can not reconnect to PLC.

The code run on ubuntu22.04 and python3.12. When PLC and python program is running, the variable can be read from PLC successfully.
If I turn off the PLC, the program will give the error message," ADSError: timeout elapsed (1861)". Then I turn on the PLC, the error will disappear and the variable can be read successfully.

However,if the PLC was turn off more then 15 minutes, the program will throw the error",Error: read frame failed with error: No route to host". Then I turn on the PLC, but I still can not read variable form PLC, the error is same as before.

The code is as following:

import pyads
import platform
import time

system = platform.system() 
release = platform.release() 




# configure ADS communication

def init_linux_ads_route(plc_netid: str = '192.168.0.20.1.1',  # PLC AmsNetId
                         linux_ip: str = '192.168.0.222',  # Liunx IP Address
                         plc_ip: str = '192.168.0.20',  # PLC IP Address
                         plc_username: str = 'Administrator',  # PLC username
                         plc_password: str = '1',  # PLC password
                         linux_route_name: str = 'eric',  # Linux hostname
                         linux_netid: str = '192.168.0.222.1.1',  # Linux AmsNetId
                         ):

    try:
        port_num = pyads.open_port()
        print(f"init ADS communication Service, port: {port_num}")

        # set AmsNetId , only available in Linux
        pyads.set_local_address(linux_netid)

    except pyads.ADSError as err:
        print(f"Error: init ADS communication failed. {err}")

    # if the system is Linux ,configure ADS router
    if system.lower() in ['ubuntu', 'linux', "ubuntu 22.0.4"]:
        try:
            # add  Linux info to PLC route
            SUCESS = pyads.add_route_to_plc(sending_net_id=plc_netid,  # PLC AmsNetId
                                            adding_host_name=linux_ip,  # Liunx IP Address
                                            ip_address=plc_ip,  # PLC IP Address
                                            username=plc_username,  # PLC username
                                            password=plc_password,  # PLC password
                                            route_name=linux_route_name,  # Linux ADS Route name
                                            added_net_id=linux_netid,  # Linux AmsNetId
                                            )
            print(f"Is connect to PLC: {SUCESS}")
        except Exception as err:
            print(f"Error: Added an ADS routing error. {err}")

        try:
            # add PLC info to Linux route
            pyads.add_route(adr=plc_netid,  # PLC AmsNetId
                            ip_address=plc_ip  # PLC IP Address
                            )


        except Exception as err:
            print(f"Error: Added an ADS routing error. {err}")
    else:
        print(f"System info: {system}")



if system.lower() in ['ubuntu', 'linux', "ubuntu 22.0.4"]:
    init_linux_ads_route()
    print("Successful initialization ADS Route.")
else:
    print(f"System info: {system}")







def get_data(timeout_ms: int = 10000, max_retries: int = 5, retry_interval: int = 1):
    # Infinite loop, read the data in the PLC memory every 1s
    while True:
        for attempt in range(max_retries + 1):

            try:
                
                port_num = pyads.open_port()
                print(f"port_num: {port_num}")

                # if the system is ubuntu,reset AmsNetId
                if system.lower() in ['ubuntu', 'linux', "ubuntu 22.0.4"]:
                    pyads.set_local_address('192.168.0.222.1.1')

                pyads.set_timeout(timeout_ms)

                # connect to  PLC port 851
                plc = pyads.Connection(ams_net_id='192.168.0.20.1.1',  # PLC AmsNetId
                                       ams_net_port=851,  # PLC Runtime Port
                                       ip_address='192.168.0.20'  # PLC IP Address
                                       )
                try:
                    plc.open()
                except Exception as err:
                    print(f"open PLC failed {err}")
                    time.sleep(60)  # ADS communication timeout, sleep 60s

                # check the connection state
                ads_state, device_state = plc.read_state()
                print(f"ADS code: {ads_state}, Device code: {device_state}")

                # read the variable in  PLC
                record_time = plc.read_by_name('MAIN.formatTime', pyads.PLCTYPE_STRING)  # 实时时间, yyyy-MM-dd HH:dd:ss.sss
                print(f"format time: {record_time}")


                # close connection
                plc.close()
                pyads.close_port()
                print(" ADS connection closed")

                time.sleep(1)

            except Exception as err:

                if attempt < max_retries:
                    print(f"  ADS connect failed {attempt + 1} times, retry in {retry_interval} second . {err}")
                    time.sleep(retry_interval)
                    # close connection
                    plc.close()
                    pyads.close_port()
                    print(" ADS connection closed")
                else:
                    # close connection
                    plc.close()
                    pyads.close_port()
                    print(" ADS connection closed")

[chrisbeardy]

The reconnection of ADS (not just pyads) is not straightforward, I've often found it to be a little annoying. I normally have a heartbeat running that I can monitor on a notification (or in your specific case here you are just polling so that also works), then if I have an error I cause the program to have to be restarted. I understand this is not practical in every case. However, looking at your code I can't see anything inherently wrong, theoretically just trying to recreate the connection as you are doing should work. I suspect the 15 minute timeout error is being caused by the underlying ADS library or some python "cacheing" of the plc / pyads instance. What happens when you restart the python program, does it now just read ok? Could you try reloading pyads after the time out too, import importlib; importlib.reload(package) and also del plc.