Bug: OpcDaClient problems with Multithreading

[jamesbraza]

I have discovered that if you try to connect the OpcDaClient on a thread, it throws an Exception. Please see the below code snippet (done with MatrikonOPC Simulation Server):

from threading import Thread

from openopc2.config import OpenOpcConfig
from openopc2.da_client import OpcDaClient

MATRIKON_SIMULATION_SERVER = "Matrikon.OPC.Simulation"

open_opc_config = OpenOpcConfig()
open_opc_config.OPC_SERVER = MATRIKON_SIMULATION_SERVER

# 1. Instantiate client in main thread
opc = OpcDaClient(open_opc_config=open_opc_config)
# 2. Connect client in another thread (doesn't work)
thread = Thread(
    target=opc.connect, kwargs={"opc_server": MATRIKON_SIMULATION_SERVER}
)
thread.start()
thread.join()
# 2. Connect client in the main thread (works)
opc.connect(opc_server=MATRIKON_SIMULATION_SERVER)
# 3. Try reading tag
result = opc.read("Random.Boolean")
_ = 0  # Debug here

If you use the main thread the whole time, this works.

If you call OpcDaClient.connect on a thread, you get this Exception when OpcCom.connect calls self.opc_client.Connect:

pywintypes.com_error(-2147352567,
                     'Exception occurred.',
                     (0, None, None, None, 0, -2147467259),
                     None)

Notable, OpenOPC (not OpenOPC 2) doesn't have this error:

from threading import Thread

import OpenOPC

MATRIKON_SIMULATION_SERVER = "Matrikon.OPC.Simulation"

# 1. Instantiate client in main thread
opc = OpenOPC.open_client("localhost")  # Open mode
# 2. Connect client in another thread (works)
thread = Thread(
    target=opc.connect, kwargs={"opc_server": MATRIKON_SIMULATION_SERVER}
)
thread.start()
thread.join()
# 3. Try reading tag
result = opc.read("Random.Boolean")
_ = 0  # Debug here

This is a bummer for me, because I use a software framework where all device connections are all made asynchronously (on a thread). I would like to use OpenOPC2, but this is an issue.