public virtual StateChangeReturn set_state
Sets the state of the element.
This function will try to set the requested state by going through all the intermediary states and calling the class's state change function
This function can return ASYNC, in which case the element will
perform the remainder of the state change asynchronously in another thread. An application can use
get_state to wait for the completion of the state change or it
can wait for a state change message on the bus.
State changes to READY or
NULL never return
||the element's new State.
|Result of the state change using StateChangeReturn. MT safe.