Recommendation to perform parallel operations

[Selvam96]

Hello All,

I'm subscribing to multiple tags. based on particular tag, I'm calling an image analysis function under datachangenotification method During the time it takes to finish the image analysis I Was not able to read and store data of other tags . I want to read the other tags value as well as to perform image analysis parellely. Working on closed loop process !. what blocks the operation ?

[swamper123]

Hey ho,

running image analysis in the datachange notification is a pretty tough task for a single core. That will be your blocking behaviour.
In an example is written:

Do not do expensive, slow or network operation there. Create another
thread if you need to do such a thing

In your case I would even say, use another process and try to handle it with that, because you won't have a good performance with threadding as well I would say.

[Selvam96]

danke @AndreasHeine . I would like to know how to start the subhandler class using multiprocessing ?

[oroulet]

@Selvam96 https://www.google.com/search?q=python+multithreading+tutorial&oq=python+multithreading+tutorial

[Selvam96]

def subscribe(client,sub_nodes):
    handler = SubHandler()
    sub = client.create_subscription(100, handler)
    sub.subscribe_data_change(sub_nodes)

if __name__ == "__main__":
    
    client = Client("opc.tcp://localhost:4840")
    client.connect()
    analysis_status = client.get_node("ns=4;s=MAIN.analysisStart")
    ntest = client.get_node("ns=4;s=MAIN.ntest")
    sub_nodes = [analysis_status,ntest]
    #p1 = threading.Thread(target=subscribe, args=(client, sub_nodes))
    p1 = multiprocessing.Process(target=subscribe, args=(client, sub_nodes))
    p1.start()

I get an error while working with multiprocess but it works fine with Threading

ie .TypeError: can't pickle _thread.lock objects

[AndreasHeine]

thats a miss understanding of threads and processes! you need to learn more about processes and understand the difference to threads... i can only encourage you to think more about program structure even if i send you a code sniped, you need to understand the paradigma behind in the first place!
https://www.youtube.com/watch?v=9zinZmE3Ogk
maybe producer/consumer architecture is a good point to start
https://stonesoupprogramming.com/2017/09/11/python-multiprocessing-producer-consumer-pattern/comment-page-1/

[Selvam96]

Thanks Andreas .. I'm happy to get a such good inputs and support . I will read more about these concepts

[oroulet]

yes put your data in some Queue object and have another thread of proces analyse it