Detect that a child is waiting for input

[unDEFER via Digitalmars-d]

On Sunday, 20 November 2016 at 21:03:57 UTC, John Colvin wrote:
> If blocking is an error, you could close stdin and assuming the 
> process checks the error codes correctly....

No, I mean blocking is not error.
One method to find it, run gdb or strace and see where the 
process stopped, or which syscall was last. But I believe that 
must be other way.