Stdlib system interaction API: call for feedback

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Nice, elegant idea! let’s try to discuss this a bit deeper cause I’m not super expert in this event-driven coding. If I want to do something similar, with the current logic I’d just do:

if (is_completed(process)) call callback(process%exit_state)

However, we could add it part of the process type as a pointer:

procedure(process_oncomplete), pointer :: callback => null()

And then when the process is completed:

! check completion
[...]
process%complete = .true.

! [...] load stdout, stderr

if (associated(process%callback)) &
call process%callback(process%exit_state,process%stdin,process%stdout,process%stderr)

So I think a good callback interface would be

abstract interface
    procedure process_oncomplete(exit_state,stdin,stdout,stderr)
        integer, intent(in) :: exit_state
        ! presence depends on allocation status in process type (<- user request)
        character(len=*), optional, intent(in) :: stdin,stdout,stderr
    end procedure process_oncomplete
end interface

Another slightly related thing is that we may want to ensure the system is not clogged with dangling processes. Should we have a finalizer?

! Process variable goes out of scope: ensure no dangling process
subroutine process_final(process)
    type(process_type), intent(inout) :: process
    logical :: success

    if (is_running(process)) call kill(process, success)
end subroutine