Whether `shared_array.py` works for ddp

Hi, ptrblck. Thanks for providing the example of sharing an array among different workers in `shared_array.py'. However, there's only one `Dataset` instance in the job. I'm wondering whether it still applies in DDP scenario when multiple instances of `Dataset` exist. I haven't tried it in DDP on my own, but I want to make sure it works in DDP first. Thanks : )