Device creation in a python subprocess freezes

AlessandroB

Hello,

while the device creation in the main thread or in a thread of the main process works fine, the program freezes if this is done in a subprocess (created through the python multiprocessing module).

Is this the expected behavior?

Thanks!

Alessandro

abroekhof

I've successfully created devices in mp.Process. Do you have a MWE?

AlessandroB

code mwe

Hi abroekhof , in the link above there is the code of the MWE.

If the acquisition_oak function is executed within a thread (line 234) it works fine, instead if within a process (line 235) it hangs at line 134 (with dai.Device(pipeline) as device🙂.

Cheers.

erik

Hi AlessandroB ,
I believe that connecting to the device has to be done in the main thread, and there must be some delay between connecting to 2 separate devices. We have a demo here that uses threading. Thoughts?
Thanks, Erik
PS. note that 250 LoC isn't very minimal🙂

AlessandroB

Hi erik ,

thank you for the clarification, it wasn't clear to me the main thread "constraint".

Sorry for the MWE length, I'll do better in the future.

Cheers

Alessandro

AlessandroB

Hi erik ,

I had a think and the issue is slightly different.

I'm able to initialize a device in a thread different from the main thread, but I fail if that happens within a different process. Instead, @abroekhof claims he's able to do so.

In my application I found a workaround, nonetheless it would be interesting to get to know if initialization within a subprocess is actually allowed.

Best

Alessandro

abroekhof

Hi @AlessandroB we're able to connect to cameras in separate processes, looks something like this.

for info in infos:
    # Converts enum eg. 'XLinkDeviceState.X_LINK_UNBOOTED' to 'UNBOOTED'
    state = str(info.state).split('X_LINK_')[1]
    logging.info(
        'Found device %s, MxId: %s, State: %s', info.name, info.mxid, state
    )
    proc = mp.Process(
        target=cam_process,
        name=info.mxid,
        args=(
            log_queue,
            info.mxid,
            data_queue,
            exit_event,
        ),
        daemon=True,
    )
    procs.append(proc)
    proc.start()

AlessandroB

Hi abroekhof ,

if I run the function in a thread it works, if in a process it hangs at the line "with dai.Device(pipeline) as device:".

It's very strange, as it works for you!

Cheers

Alessandro

abroekhof

Oh, one other thing to try, put

mp.set_start_method('spawn')

at the top of your main function.

AlessandroB

Hi abroekhof ,

with this process start method it works!!!

Thank you very much!!

Alessandro