(subshell=$BASHPID
  (kill $subshell && wait $subshell 2>/dev/null) &
sleep 600)

echo subshell done
	
./test.sh: line 4:  5439 Terminated              ( subshell=$BASHPID; ( kill $subshell && wait $subshell 2> /dev/null ) & sleep 600 )
subshell done