Realsense cannot be instantiated more than once with multiprocessing

[m-decoster]

Describe the bug

RuntimeError: Frame didn't arrive within 5000

This is the same issue as #109 which was fixed in #115 for single process code.

The fix does not work when used with the multiprocessing package

To Reproduce

Below script:

# Set up multiprocessing camera.
namespace = "camera"

# Creating and starting the publisher
p = MultiprocessRGBPublisher(
    Realsense,
    camera_kwargs={
        "resolution": Realsense.RESOLUTION_720,
        "fps": 30,
        "enable_hole_filling": True,
    },
    shared_memory_namespace=namespace,
)
p.start()

self._camera = MultiprocessRGBReceiver(namespace)
self._rerun_logger = MultiprocessRGBRerunLogger(namespace)
self._rerun_logger.start()

Realsense will fail to send frames

Expected behavior

This should start and log images to rerun, but it only does so after replugging the USB cable (as was the case in the original issue)

[tlpss]

hm weird that it no longer works for the multiprocessing case. Could it be due to faulty resource management somehow? (i.e. closing the receivers without properly closing the camera?) @Victorlouisdg any thoughts?

[tlpss]

maybe related to #98

[Victorlouisdg]

There's a few things we can investigate:

• are you sure the publisher process has terminated and thus released the handle on the camera hardware?
• if it was terminated: was the __exit__ method of the RealSense object called and thus pipeline.stop()?
• if that was called, is the devices listed in the call to devices = ctx.query_devices() used by the fix?