[distributed env] potentially unsafe parallel execution
You can pass the same `experiment_id` for all the metrics of the same group, and use another `experiment_id` for the other groups.
Maybe we can add an environment variable that sets the default value for `experiment_id` ? What do you think ? Ah, you're absolutely correct, @lhoestq - it's exactly the equivalent of the shared secret. Thank you!
```
metric = load_metric('glue', 'mrpc', num_process=num_process, process_id=rank)
```

presumes that there is only one set of parallel processes running - and will intermittently fail if you have multiple sets running as they will surely overwrite each other. Similar to https://github.com/huggingface/datasets/issues/1942 (but for a different reason).
That's why dist environments use some unique to a group identifier so that each group is dealt with separately. 

e.g. the env-way of pytorch dist syncing is done with a unique per set `MASTER_ADDRESS+MASTER_PORT`

So ideally this interface should ask for a shared secret to do the right thing.

I'm not reporting an immediate need, but am only flagging that this will hit someone down the road.

This problem can be remedied by adding a new optional `shared_secret` option, which can then be used to differentiate different groups of processes. and this secret should be part of the file lock name and the experiment.

Thank you