close multiprocessing safely

[yangia]

I think

workers.close()
workers.join()

should be added right before the return xxx in method combine_to_panoptic_multi_core and pq_compute_multi_core for closing multiprocessing safely, as my collegue found it might not release the memory properly. I agreed and adopted it, but I didn't test it.

[penguinflys]

I found the problem too, this has actually caused several downtimes at the server of my boss. I have tested it, and it works well now.

[Basseldonk]

Agreed. Not closing led to memory leaking problems. The solution proposed by @yangia solved the problem for me.

[dahliau]

Agreed. @yangia thanks for that.
I test it, and workers.close() is enough to close the process.