Option to limit concurrency

[faximan]

jobs==0 means "no limit concurrency.", which seems to be the case reading https://github.com/keith/rules_multirun/blob/e2245c6a4e1fb26cea7db6fac16d856693cf1ec1/internal/multirun.py:

processes = [
        (command, _run_command(command, block=False, **kwargs))
        for command
        in commands
    ]

We are considering using this in a deployment job to run hundreds of targets, each releasing a single build artifacts to some external store, but we don't want to spawn hundreds of processes in parallel. It would be great if the parallelism was configurable, or default limited to e.g. the number of CPU cores.

https://stackoverflow.com/questions/9808714/control-the-number-of-subprocesses-using-to-call-external-commands-in-python has some implementation ideas for this use case.

[keith]

see also #55

[faximan]

Ack, thanks for the pointer. I had missed that PR. FWIW, we do not care about the stdin features if those have to be mutually exclusive.