Add a run_in_background option for executables

[linsword13]

No description provided.

[douglasjacobsen]

One small question.

As an aside, is it useful to capture the PID of the backgrounded process, so we can do something like sleep until it's finished?

[linsword13]

One small question.

As an aside, is it useful to capture the PID of the backgrounded process, so we can do something like sleep until it's finished?

Yeah good call. I was thinking to have a modifier to achieve that (using an executable_modifier to capture the PID,) and then do a wait-for-all at the end. I feel that might be more flexible. Will add such a modifier in this PR.

[linsword13]

One small question.
As an aside, is it useful to capture the PID of the backgrounded process, so we can do something like sleep until it's finished?

Yeah good call. I was thinking to have a modifier to achieve that (using an executable_modifier to capture the PID,) and then do a wait-for-all at the end. I feel that might be more flexible. Will add such a modifier in this PR.

Added a modifier doing the wait-for-completion for background jobs.

[douglasjacobsen]

Thanks for making the changes! This is awesome.

One small comment, otherwise it LGTM. Feel free to choose between adding the conditional check or adding a comment in the doc string.