Error in watchdog loop

[TommyTomson585]

Hey there,

I am using the library to connect to a OPC Server of a welding machine. The client creates a subcription and resubscribes if it looses the connection.

I am using the asyncua in the version 1.0.3 an python 3.11

Let me say that I am just a "user" of the code. My knowledge is very basic or low level.

Here a snip of the code. It is just the "handler class" and the definition of the opcua_client() method.

`

 import asyncio
from asyncua import Client, Server, ua, Node
import datetime
from time import sleep
import logging

....

class SubHandler:
    def __init__(self):
        self.initial = True

        

        
     
          
   
async def datachange_notification(self, node: Node, val, data):
       
            global valCounter1, valCounter2
        
            async with datachange_notification_queue_lock:
                datachange_notification_queue.append((node,val,data))
        
                print("Node hat den Status geaendert. Aktueller Wert:",node, val)

                if node == itemlist[0]:
                    
                    if val is not None:
                        
                        if valCounter1 is None:
                            
                            valCounter1= val
                        
                        else:
                            
                            if val > valCounter1:
            
                                valCounter1=val
            
                   
                                await asyncio.sleep(1)
                
                                if station1.getValue() == None:
                                    print("Station1 leer" )
                                else:   
                                    print("Station1"  + station1.getValue())

                                if station2.getValue() == None:
                                    print("Station2 leer")
                                else:    
    
                                    print("Station2"  + station2.getValue())
               
                                if station1.getValue() == station2.getValue():
                                    counterBerghaus.doInkre()
                
                                elif station1.getValue() != station2.getValue():
                                    counterBerghaus.inkre()
                        
                    #if self.initial==True:
                        
                        #self.initial=False
                        
                    #else:
                                
                                await countState.set_value(counterBerghaus.getValue())
                  
                                await write()
                                await aufzeichner3()
                
                
                elif node == itemlist[1]:
                    
                    if val is not None:
                        
                        if valCounter2 is None:
                            
                            valCounter2= val
                            
                        else:
                            
                            if val > valCounter2:
                      
                
                                valCounter2 = val
                                await asyncio.sleep(1)
                
                elif node == itemlist[2]:
               
                    station1.setValue(val)
                    await aufzeichner3()
                
                elif node == itemlist[3]:
                
                    station2.setValue(val)
                    await aufzeichner3()
            
                elif node == itemlist[4]:
                    valState=val
                    valState=bool(valState)
                    global statusRob
                    statusRob = valState
                    
                    
                    await servState.set_value(valState)
                    await aufzeichner3()
                
        
            
      
    def event_notification(self, event):
        
        print("Python: New event", event)

async def opcua_client():
    
       
    
        client = Client(url=ServerUrl)
        
        
        
        itemlist.append(client.get_node(counter1))
        itemlist.append(client.get_node(counter2))
        itemlist.append(client.get_node(product1))
        itemlist.append(client.get_node(product2))
        itemlist.append(client.get_node(status))
        #itemlist.append(client.get_node(serverStatus))
       
       
       
       
        #client=Client("opc.tcp://Berghaus-WS26:4980/Softing_dataFEED_OPC_Suite_Configuration1")
        
        handler= SubHandler()
        subscription = None
        
        case = 0
        subscription_handle_list=[]
        idx = 0
        
        while 1:
            if case ==1:
                #connect
                print("connecting...")
                try:
                    await client.connect()
                    print("connected!")
                    case = 2
                    
                except:
                    print("connection error!")
                    case = 1
                    await  asyncio.sleep(2)
            elif case == 2:
                
                #subscribing nodes and events
                
                print("subscribing nodes and events.....")
                
                try:
                    subscription = await client.create_subscription(200, handler)
                    subscription_handle_list = []
                    if nodes_to_subscribe:
                        for node in nodes_to_subscribe:
                            handle = await subscription.subscribe_data_change(client.get_node(node))
                            subscription_handle_list.append(handle)
                    print("subscribed!!")
                    
                    case = 3
                except:
                    print("subscription error!!")
                    
                    case= 4
                    await asyncio.sleep(0)
            elif case == 3:
                
                try:
                    #service_level = await client.get_node("ns=12;s=Robo3_OPC.nsuri=http://opcfoundation.org/UA/;n=2259").get_value()
                    service_level = await client.get_node("ns=0;i=2256").get_value()
                    
                    
                    if service_level:
                        
                        case = 3
                        
                    else:
                        
                        case = 4
                    await asyncio.sleep(2)
                    
                except:
                    
                    case = 4
            
            elif case == 4:
                
                print("unsubscribing....!!")
                
                try:
                    
                    if subscription_handle_list:
                        for handle in subscription_handle_list:
                            await subscription.unsubscribe(handle)
                    
                    await subscription.delete()
                    print("unsubscribed!!!")
                
                except:
                    
                    print("unsubscription error!!!")
                    
                    subscription = None
                    subscription_handle_list = []
                    await asyncio.sleep(0)
                
                print("disconnecting...")
                
                try:
                    
                    await client.disconnect()
                
                except:
                    
                    print ("disconnection error!")
                
                case = 0
                
            else:
                
                case = 1
                await asyncio.sleep(2)

`

The client is working fine but from time to time I have an exception:

Here a part of the logfile when the error appears:

.
.

.
count_inkretwo
14094
Node hat den Status geaendert. Aktueller Wert: ns=5;s=MotionDeviceSystem.Controllers.Controller_1.ProcessData.Partcounter.Partcounter_St2 28703
Node hat den Status geaendert. Aktueller Wert: ns=5;s=MotionDeviceSystem.Controllers.Controller_1.ProcessData.State.ARC_ON 0
Node hat den Status geaendert. Aktueller Wert: ns=5;s=MotionDeviceSystem.Controllers.Controller_1.ProcessData.Productinfo.Productinfo_St1 RG15844524
Node hat den Status geaendert. Aktueller Wert: ns=5;s=MotionDeviceSystem.Controllers.Controller_1.ProcessData.Productinfo.Productinfo_St2 RG-15844524
Node hat den Status geaendert. Aktueller Wert: ns=5;s=MotionDeviceSystem.Controllers.Controller_1.ProcessData.State.ARC_ON 1
Node hat den Status geaendert. Aktueller Wert: ns=5;s=MotionDeviceSystem.Controllers.Controller_1.ProcessData.State.ARC_ON 0

Error in watchdog loop
Traceback (most recent call last):
File "C:\Users\Thomas.Hartz\AppData\Local\Programs\Python\Python311\Lib\asyncio\tasks.py", line 490, in wait_for
return fut.result()
^^^^^^^^^^^^
asyncio.exceptions.CancelledError

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
File "C:\Users\Thomas.Hartz\AppData\Local\Programs\Python\Python311\Lib\site-packages\asyncua\client\client.py", line 520, in _monitor_server_loop
_ = await self.nodes.server_state.read_value()
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Thomas.Hartz\AppData\Local\Programs\Python\Python311\Lib\site-packages\asyncua\common\node.py", line 179, in read_value
result = await self.read_data_value()
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Thomas.Hartz\AppData\Local\Programs\Python\Python311\Lib\site-packages\asyncua\common\node.py", line 190, in read_data_value
return await self.read_attribute(ua.AttributeIds.Value, None, raise_on_bad_status)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Thomas.Hartz\AppData\Local\Programs\Python\Python311\Lib\site-packages\asyncua\common\node.py", line 304, in read_attribute
result = await self.session.read(params)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Thomas.Hartz\AppData\Local\Programs\Python\Python311\Lib\site-packages\asyncua\client\ua_client.py", line 397, in read
data = await self.protocol.send_request(request)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Thomas.Hartz\AppData\Local\Programs\Python\Python311\Lib\site-packages\asyncua\client\ua_client.py", line 160, in send_request
data = await asyncio.wait_for(self._send_request(request, timeout, message_type), timeout if timeout else None)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Thomas.Hartz\AppData\Local\Programs\Python\Python311\Lib\asyncio\tasks.py", line 492, in wait_for
raise exceptions.TimeoutError() from exc
TimeoutError
DataChange subscription has no status_change_notification method
unsubscribing....!!
unsubscription error!!!
disconnecting...
disconnection error!
connecting...
connection error!
connecting...
connection error!
connecting...
connection error!
connecting...
connection error!
connecting...
connection error!
connecting...
connected!
subscribing nodes and events.....
Revised values returned differ from subscription values: CreateSubscriptionResult(SubscriptionId=1155306408, RevisedPublishingInterval=200.0, RevisedLifetimeCount=18000, RevisedMaxKeepAliveCount=6000)
subscribed!!
Node hat den Status geaendert. Aktueller Wert: ns=5;s=MotionDeviceSystem.Controllers.Controller_1.ProcessData.Partcounter.Partcounter_St1 28676
Station1RG15844524
Station2RG-15844524
Count_inkre
14094
Node hat den Status geaendert. Aktueller Wert: ns=5;s=MotionDeviceSystem.Controllers.Controller_1.ProcessData.Partcounter.Partcounter_St2 28703
Node hat den Status geaendert. Aktueller Wert: ns=5;s=MotionDeviceSystem.Controllers.Controller_1.ProcessData.State.ARC_ON 1
Node hat den Status geaendert. Aktueller Wert: ns=5;s=MotionDeviceSystem.Controllers.Controller_1.ProcessData.Productinfo.Productinfo_St1 RG15844524
Node hat den Status geaendert. Aktueller Wert: ns=5;s=MotionDeviceSystem.Controllers.Controller_1.ProcessData.Productinfo.Productinfo_St2 RG-15844524

Has anyone an idea why this error in the watchdog loop appears?

Thanks ahead for your support.

Kind regards

Thomas

[schroeder-]

The watchdog loop is to detect if the connection is lost. So this error is triggered if the server is not reachable.

[TommyTomson585]

Thank you for your reply.

Okay I got it. But shouldn't that be catched by an exception?

[schroeder-]

you can call check_connection periodical, this will throw the exception. Or add status_change_notification in your subscription handler.