void onSubchannelState(ConnectivityStateInfo newState)
The initial state of a Subchannel is IDLE. You won't get a notification for the initial IDLE state.
If the new state is not SHUTDOWN, this method should create a new picker and call
Helper.updateBalancingState(). Failing to do so may result in
unnecessary delays of RPCs. Please refer to
PickResult.withSubchannel()'s javadoc for more information.
SHUTDOWN can only happen in two cases. One is that LoadBalancer called
LoadBalancer.Subchannel.shutdown() earlier, thus it should have already discarded this Subchannel. The
other is that Channel is doing a
forced shutdown or has
already terminated, thus there won't be further requests to LoadBalancer. Therefore, the
LoadBalancer usually don't need to react to a SHUTDOWN state.
newState- the new state