void onSubchannelState(ConnectivityStateInfo newState)Handles a state change on a Subchannel.
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.
When a subchannel's state is IDLE or TRANSIENT_FAILURE and the address for the subchannel was received in
LoadBalancer.handleResolvedAddresses(io.grpc.LoadBalancer.ResolvedAddresses), load balancers should call
LoadBalancer.Helper.refreshNameResolution()to inform polling name resolvers that it is an appropriate time to refresh the addresses. Without the refresh, changes to the addresses may never be detected.
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 shutdownor 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