yield
task 1
set event
yield
wait task
task 1 done
----
yield
task 2
set event
yield
schedule
schedule done
wait task
task 2 done
----
set event
yield
task 3
task 3 done
wait task
----
set event
yield
clear event
yield
yield
task 4
set event
yield
wait task
task 4 done
