Crash in easyopencv when attempting to stop streaming on a VisionPortal

For an orderly shutdown of Autonomous we are attempting to disable a processor, stop streaming on the VisionPortal instance, and then call close() on the VisionPortal. The call to disable the processor completes but then on the next call to stopStreaming(0 we get this in our matchlog
--------- beginning of crash
11-21 09:37:52.323 1723 1964 E AndroidRuntime: FATAL EXCEPTION: Thread-48
11-21 09:37:52.323 1723 1964 E AndroidRuntime: Process: com.qualcomm.ftcrobotcontroller, PID: 1723
11-21 09:37:52.323 1723 1964 E AndroidRuntime: java.lang.NullPointerException: Attempt to invoke interface method ‘void org.openftc.easyopencv.OpenCvCamera.stopStreaming()’ on a null object reference

Nowhere do we access easyopencv directly - we only use the VisionPortal.

Phil Young
FTC Team 4348

The VisionPortal uses EasyOpenCV on the backend. EasyOpenCV is used for all VisionPortal displays on the Driver Station and Robot Controller, and is also used to perform all AprilTag detection.

I’m sure you probably realize this, but I am going to say it for those who may not be aware, in order to safely clean up you generally have to work in reverse order of how you started it up - this goes for virtually all resource allocation use, not just the VisionPortal.

From your description, it’s difficult to tell that you’re following the proper steps. Can you post the appropriate snippet of your cleanup code so we can ensure the resources are being torn down in the appropriate sequence?


Note that VisionPortal automagically performs an orderly shutdown when the OpMode is stopped regardless of whether the user tries to manually teardown anything or not.

Could you post a minimal, complete, and verifiable example OpMode that demonstrates the issue? From looking at the implementations, I think what is happening is there is a race condition between the automatic cleanup and your manual cleanup.

OK, I have a reliable test case based on the sample ConceptAprilTag. This week we’re desperately getting ready for our Meet 2 next weekend but I should be able to find some time to create a Gist.

Here is the link to a public gist that contains my modified version of ConceptAprilTag and the matchlog of the crash.