Validator hangs in MonoCameraValidator.generateMovoview() when called from CameraChainValidator.synchronizedCallback

[brawner]

It's unclear why this is an issue only for me, but the validator hangs for me when after it brings up all the cv2 windows. As I understand it's likely because the GUI calls happening inside a ROS message subscriber, which is being executed in a separate thread.

I believe it's only recommended to interact with the CV2 gui's from the main thread, which is not necessarily the case if you are calling the gui API from within a ROS subscriber callback. In that case, subscriber callbacks should be only adding images to a SPSC queue, which are updated in a while loop in main. Since there is no "spin once" for ros python, that would imply the rospy.spin() would need to run in a background thread and feed images for viewing to the main thread.

https://stackoverflow.com/a/60739664/2089061 https://github.com/opencv/opencv/issues/8407

If you have any recommended workarounds to this issue, that would be very helpful. Thank you

[goldbattle]

Can you provide details of the OS you are using and library version (opencv, ros etc)?

On Wed, Jun 22, 2022 at 6:21 PM Stephen Brawner @.***> wrote:

It's unclear why this is an issue only for me, but the validator hangs for me when after it brings up all the cv2 windows. As I understand it's likely because the GUI calls happening inside a ROS message subscriber, which is being executed in a separate thread.

I believe it's only recommended to interact with the CV2 gui's from the main thread, which is not necessarily the case if you are calling the gui API from within a ROS subscriber callback. In that case, subscriber callbacks should be only adding images to a SPSC queue, which are updated in a while loop in main. Since there is no "spin once" for ros python, that would imply the rospy.spin() would need to run in a background thread and feed images for viewing to the main thread.

https://stackoverflow.com/a/60739664/2089061 opencv/opencv#8407 https://github.com/opencv/opencv/issues/8407

If you have any recommended workarounds to this issue, that would be very helpful. Thank you

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[brawner]

Ubuntu 20.04, ROS noetic. Using the master branch of Kaliber with opencv-python == 4.6.0.66