Client can't get notification until method complete

[frinklai]

Describe the bug

[What I do]

1. Create an UA server with a method that can trigger an event

2. Create UA clientA which register the event.

3. Create clientB and use it to trigger event by call ua method.

[ISSUE]

• I found when I use another ua clientB to call UA_method_for_trigger_event, the event_notification in clientA will executed until UA_method_for_trigger_event complete.

• Is there any way to let client get notification immediately, while event_generator trigger signal

[Simple example code are as follows:]

[server.py]

    def UA_method_for_trigger_event():   # <====== Suppose this is an UA method in UA server.
        event_generator.trigger(message="")
        time.sleep(30)

[clientA.py]

    class UASubscriber(object):
        def __init__(self):
           pass 

        def event_notification(self, event):
            # Will execute until  'UA_method_for_trigger_event ' in server complete   <====== ISSUE
            data = event.get_event_props_as_fields_dict()
            print("data = ", data)

Expected behavior

Is there any way to let client get notification while event_generator.trigger event_generator.trigger singal

Version

python 3.8

[frinklai]

BTW
I just found the problem is the if condition in below code is not true,
but I still have no idea about why and how to solve it

internal_subscription.py - _pop_triggered_events

[oroulet]

not sure either but you should really use asyncua and not python-opcua...

[AndreasHeine]

ua-methods aren't supposed to have long execution times like more then a few seconds for those usecases opc ua has defined "Part 10 Programs" https://reference.opcfoundation.org/Core/Part10/4.1/

.trigger() just creates and appends a event-notification to the queue which will be emptied in the next publishinterval

[oroulet]

But it is strange that that call hangs the processing of events. Even if such a long call should not be done.
If asyncua has the same issue might need to have a look

[AndreasHeine]

if you follow the trigger method you will end up in internal subscription append to queue... from first view there cant hang anything ^^

python-opcua/opcua/server/event_generator.py

Line 109 in 96a8ea6

self.isession.subscription_service.trigger_event(self.event)

python-opcua/opcua/server/internal_subscription.py

Line 230 in 96a8ea6

def _trigger_event(self, event, mid):

[oroulet]

Might be the same thread doing both things. You cannot have so many threads in python. I think i fixed/improved something like that in asyncua once

[AndreasHeine]

@oroulet

from the data it looks correct but with ua expert i can confirm that it shows the event after the call is done!?

Publish interval of the Event subscription is at 500ms so a lot faster then the 5s sleep!

Testcode:

import asyncio
import logging
from asyncua import ua
from asyncua.server import Server, EventGenerator
import datetime

# logging.basicConfig(level=logging.INFO)
# _logger = logging.getLogger('asyncua')

async def main():
    server = Server()
    await server.init()
    server.set_endpoint("opc.tcp://0.0.0.0:4840/freeopcua/server/")
    # setup our own namespace, not really necessary but should as spec
    uri = "http://examples.freeopcua.github.io"
    idx = await server.register_namespace(uri)
    # populating our address space
    myobj = await server.nodes.objects.add_object(idx, "MyObject")

    myevgen = await server.get_event_generator(ua.ObjectIds.BaseEventType, myobj)

    async def func(parent, variant):
        print("Calltimestamp", datetime.datetime.now())
        myevgen.event.Message = ua.LocalizedText("MyFirstEvent %d" % variant.Value)
        myevgen.event.Severity = 500
        await myevgen.trigger()
        await asyncio.sleep(5)
        print("Donetimestamp", datetime.datetime.now())
        ret = False
        if variant.Value % 2 == 0:
            ret = True
        return [ua.Variant(ret, ua.VariantType.Boolean)]

    await myobj.add_method(idx, "mymethod", func, [ua.VariantType.Int64], [ua.VariantType.Boolean])

    async with server:
        while True:
            await asyncio.sleep(1)


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

[frinklai]

@AndreasHeine @oroulet
Got it, thanks very much for your test code and suggestions, I will try to using async opcua in my project.

[AndreasHeine]

@frinklai the timestamps are looking correct can you tell me what clientA (the subscribing one) is? UaExpert or a different tool / software?

just to make sure its not just uaexpert making some sync thread stuff with the ui...

[frinklai]

@AndreasHeine Both client A and client B are a python script.
I think maybe I need to use async opcua, rather than python-opcua, so that event can trigger immediately.
Is that right?