sync.Clinet is not reusable

[okapies]

Describe the bug Calling connect() on sync.Client after disconnect() will raise ThreadLoopNotRunning error.

To Reproduce

>>> client = Client('opc.tcp://localhost')
>>> client.connect()
>>> client.disconnect()
>>> client.connect()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/user/project/venv/lib/python3.10/site-packages/asyncua/sync.py", line 95, in wrapper
    result = self.tloop.post(aio_func(*args, **kwargs))
  File "/home/user/project/venv/lib/python3.10/site-packages/asyncua/sync.py", line 51, in post
    raise ThreadLoopNotRunning(f"could not post {coro}")
asyncua.sync.ThreadLoopNotRunning: could not post <coroutine object Client.connect at 0x7faf0b51ace0>

Expected behavior (Re-)initialize tloop every time we call connect().

Version

• Python-Version: 3.10
• opcua-asyncio Version (e.g. master branch, 0.9): 1.0.2

[oroulet]

This is really common. You cannot restart a Thread object. But the error message is is really hard to understand...we need to improve that..

[okapies]

Yes, but the async Client is reusable instead. This is problematic especially when want to combine both versions. Can we fix to start the thread when connect instead of __init__?

[miki5799]

Same is happening to me and I agree with your proposed expected behaviour.

[aclementptw]

I'd like to bump this, as we are currently migrating from opcua to opcua-asyncio using the wrapper functions. We do reuse Clients and this poses a problem for us.

[miki5799]

Yes, but the async Client is reusable instead. This is problematic especially when want to combine both versions. Can we fix to start the thread when connect instead of __init__?

Hello everyone,

I have submitted a PR #1503, in which a new thread is started analogous to __init__ iff the ThreadLoop has stopped, so that the updated connect method looks like this:

def connect(self) -> None:
    if not self.tloop.is_alive():
        self.tloop = ThreadLoop()
        self.tloop.start()
        self.close_tloop = True
    self.tloop.post(self.aio_obj.connect())

Analogous for the Server's start method.

This now ensures reusability of client and server, allowing a smoother migration, as mentioned by @aclementptw.