# Can't stop acquisition: try\_stop() freezes python process **URL:** \ **Category:** Python API\ **Tags:** acquisition\ **Created:** [January 18, 2022, 2:00pm UTC](https://forum.commonvisionblox.com/t/cant-stop-acquisition-try-stop-freezes-python-process/1586 "2022-01-18T14:00:51Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Swaab](https://avatars.discourse-cdn.com/v4/letter/s/ecd19e/32.png) [@Swaab](https://forum.commonvisionblox.com/u/Swaab)\ **Post date:** [January 18, 2022, 2:00pm UTC](https://forum.commonvisionblox.com/t/cant-stop-acquisition-try-stop-freezes-python-process/1586/1 "2022-01-18T14:00:51Z")
Hi! This is partially related to [Acquisition stuck when terminating early](https://forum.commonvisionblox.com/t/acquisition-stuck-when-terminating-process-early/1390) We have a system in which we make many small captures in quick succession of each other. The captures are split because they require different settings. Currently, we open the stream to take pictures, and then when we have enough we try to stop (or abort) the stream. Often this goes well, but sometimes it gets stuck in stream.try\_stop(). The code just ‘freezes’ without Exception, also doesn’t terminate. _Above also tested for try\_abort, and multi/continuous mode) It happens after a random amount of captures, in either of the cameras we’re using (no consistencies found yet). We use two cameras that are coupled in a “master-slave” configuration_ 1. How/when can this happen? 2. Is there a better way to start/stop the acquisition? We currently use a MultiFrame for capturing. It would be better to keep the stream running, and just like in Genicam use AcquisitionStart to reinitiate a capture, but I haven’t figured out a way of doing this through the python API? 3. Is there a way to force terminate the acquisition (see [Acquisition stuck when terminating early](https://forum.commonvisionblox.com/t/acquisition-stuck-when-terminating-process-early/1390) , after I would reconnect to the device after such an error?) configuration: - windows 10, 64 bit - python version: 3.8.8 - CVB version: 13.04.004 (x64) - camera: [GO-5000M-PGE (usb3)](https://www.stemmer-imaging.com/media/uploads/cameras/jai/10/103557-JAI_GO-5000_USB_Manual.pdf) Thx in advance! ---
**Author:** ![johang](https://avatars.discourse-cdn.com/v4/letter/j/ecc23a/32.png) [@johang](https://forum.commonvisionblox.com/u/johang)\ **Post date:** [January 18, 2022, 5:56pm UTC](https://forum.commonvisionblox.com/t/cant-stop-acquisition-try-stop-freezes-python-process/1586/2 "2022-01-18T17:56:21Z")
Copy that! The same happend to me. I finally got it reasonable good by putting cam start/stop in a daemon thread. This is my flow: 1. Main program starts a “recording thread” (daemon thread) 2. Recording thread starts and stops cam/stream once before starting the actual recording. 3. Main program waits a while for a “CAM OK” state from the recording thread. 4. If the “CAM OK” state doesn’t show up we know the recording thread is hanging. 5. The main program makes a system exit() which kills the daemon thread. (I haven’t found a good way of killing a hanging thread in Python?) 6. A third “defibrillator” program checks if my main program is running and restarts if necessary. It looks crazy complicated and I totally agree. It shouldn’t have to be like this but it works pretty well now. I’ll attach part of the defibrillator code so you can save some time on those annoying things😉 -------- “defibrillator” code -------- I removed a few things so it might not be running directly😊 I start the Python scripts from .bat files hence the CMD stuff and 2 processes (cmd & python). ```python running_state = DefibrillatorState.NORMAL class DefibrillatorState(Enum): NORMAL = 0 RESTARTED = 1 XXX_FAIL = 2 def check_processes(): global running_state try: python_rec_proc=None cmd_rec_proc=None # Find processes of interest for proc in psutil.process_iter(['pid', 'name', 'cmdline', 'cpu_percent']): # Get CMD processes if proc.name().startswith("cmd") and len( proc.cmdline() ) > 2: if "run_REC.bat" in proc.cmdline()[2]: cmd_rec_proc = proc # Get Python processes if proc.name().startswith("python") and len( proc.cmdline() ) > 1: if "recording.py" in proc.cmdline()[1]: python_rec_proc = proc # Do the process validation if python_rec_proc==None or running_state == DefibrillatorState.XXX_FAIL: # Python recording has died. Do a safety kill on CMD and PY and restart kill_proc(python_rec_proc, "Python recorder") kill_proc(cmd_rec_proc, "CMD RECORDING") time.sleep(1) os.system("start cmd /c run_REC.bat") running_state = DefibrillatorState.RESTARTED else: if running_state == DefibrillatorState.RESTARTED: running_state = DefibrillatorState.NORMAL except Exception as e: logging.warning(f"Exception during checking of processes: {e}") except KeyboardInterrupt: logging.info("Defibrillator received CTRL-C. Exiting.") sys.exit(2) def kill_proc(proc, proc_name): try: if proc == None: logging.debug(f"---{proc_name} was not running") else: logging.debug(f"---Killing {proc_name}") proc.kill() except Exception as e: logging.debug(f"Exception during killing of {proc_name}: {e}") if __name__ == ' __main__': logging.debug(f"DEFIBRILLATOR is running...") while True: time.sleep(15) check_processes() ``` ---
**Author:** ![Chris](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.commonvisionblox.com/chris/32/1154_2.png) [@Chris](https://forum.commonvisionblox.com/u/Chris)\ **Post date:** [January 24, 2022, 7:47am UTC](https://forum.commonvisionblox.com/t/cant-stop-acquisition-try-stop-freezes-python-process/1586/3 "2022-01-24T07:47:07Z")
Hi @Swaab , have you tried to use the try\_abort()? The reason is, that the try\_stop() waits for the current image, if this is not delivered, it will wait for ever. try\_abort() on the other hand simply cancels any ongoing waits. The timeout after which a possible active wait will be canceled is infinite per default (exception: CompositeStreamBase Streams). The new acquisition stack has an overload for the try\_stop() to pass a timeout after which the acquisition will be cancelled. [Gen 3 acq stack](https://help.commonvisionblox.com/NextGen/14.0/md_theory_of_operation_image_manager __migration_guide__ acquisition_stack.html) (C++ examples only, python works pretty much the same) Cheers Chris ---
**Author:** ![Swaab](https://avatars.discourse-cdn.com/v4/letter/s/ecd19e/32.png) [@Swaab](https://forum.commonvisionblox.com/u/Swaab)\ **Post date:** [January 25, 2022, 8:34am UTC](https://forum.commonvisionblox.com/t/cant-stop-acquisition-try-stop-freezes-python-process/1586/4 "2022-01-25T08:34:53Z")
Hi Johang! Thx for sharing your knowledge and code. I had the same consideration but I’m hoping there is a simpler approach before spending some time on it 😅. If not will definitely try to implement it! ---
**Author:** ![Swaab](https://avatars.discourse-cdn.com/v4/letter/s/ecd19e/32.png) [@Swaab](https://forum.commonvisionblox.com/u/Swaab)\ **Post date:** [January 25, 2022, 8:40am UTC](https://forum.commonvisionblox.com/t/cant-stop-acquisition-try-stop-freezes-python-process/1586/5 "2022-01-25T08:40:20Z")
@Chris I have tested try\_abort(), abort(), stop(), try\_stop() independently, in combination with a stream.wait, and a stream.wait\_for(10). Execution still freezes on the try\_abort(). That was tested yesterday in combination with the stream\_wait\_for(10). Next week I’ll have some time to extract the class from our system and I’ll try to build a simpler testable script in hope of reproducing the problem. Any other ideas of what could be the problem in the meantime? ---
**Author:** ![Chris](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.commonvisionblox.com/chris/32/1154_2.png) [@Chris](https://forum.commonvisionblox.com/u/Chris)\ **Post date:** [January 25, 2022, 9:18am UTC](https://forum.commonvisionblox.com/t/cant-stop-acquisition-try-stop-freezes-python-process/1586/6 "2022-01-25T09:18:53Z")
Hi @Swaab , I forwarded the information you provided to some of my colleagues to see if someone actually has another idea on what we could do here. What would be a great help for us to try and reproduce the problem would be an example script we can run that shows the problem. If you could send us over an example that would be great… I think you are already in contact with one of my colleagues?!