import ray

@ray.remote
def f():
    return 1

ray.init(num_cpus=1)
print(ray.get(f.remote()))
ray.shutdown()

ray.init(num_cpus=1)
print(ray.get(f.remote()))
ray.shutdown()

The above script will hang at the second ray.get(f.remote()) with error message This worker was asked to execute a function that it does not have registered. You may have to restart Ray. This is because the function is only registered to the first GCS.

I discovered this issue when I was trying to consolidating python tests in travis, see

Similar but not the same with #3897