Package io.grpc.util

Class ForwardingLoadBalancer

java.lang.Object

io.grpc.LoadBalancer

io.grpc.util.ForwardingLoadBalancer

Direct Known Subclasses:

GracefulSwitchLoadBalancer

@ExperimentalApi("https://github.com/grpc/grpc-java/issues/1771")
public abstract class ForwardingLoadBalancer
extends LoadBalancer

Nested Class Summary

Nested classes/interfaces inherited from class io.grpc.LoadBalancer

LoadBalancer.CreateSubchannelArgs, LoadBalancer.ErrorPicker, LoadBalancer.Factory, LoadBalancer.FixedResultPicker, LoadBalancer.Helper, LoadBalancer.PickDetailsConsumer, LoadBalancer.PickResult, LoadBalancer.PickSubchannelArgs, LoadBalancer.ResolvedAddresses, LoadBalancer.Subchannel, LoadBalancer.SubchannelPicker, LoadBalancer.SubchannelStateListener

Field Summary

Fields inherited from class io.grpc.LoadBalancer

ATTR_HEALTH_CHECKING_CONFIG, DISABLE_SUBCHANNEL_RECONNECT_KEY, EMPTY_PICKER, HAS_HEALTH_PRODUCER_LISTENER_KEY, HEALTH_CONSUMER_LISTENER_ARG_KEY, IS_PETIOLE_POLICY

Constructor Summary

Constructors

Constructor	Description
ForwardingLoadBalancer()

Method Summary

Modifier and Type	Method	Description
boolean	canHandleEmptyAddressListFromNameResolution()	Whether this LoadBalancer can handle empty address group list to be passed to LoadBalancer.handleResolvedAddresses(ResolvedAddresses).
protected abstract LoadBalancer	delegate()	Returns the underlying balancer.
void	handleNameResolutionError(Status error)	Handles an error from the name resolution system.
void	handleResolvedAddresses(LoadBalancer.ResolvedAddresses resolvedAddresses)	Handles newly resolved server groups and metadata attributes from name resolution system.
void	handleSubchannelState(LoadBalancer.Subchannel subchannel, ConnectivityStateInfo stateInfo)	Deprecated.
void	requestConnection()	The channel asks the LoadBalancer to establish connections now (if applicable) so that the upcoming RPC may then just pick a ready connection without waiting for connections.
void	shutdown()	The channel asks the load-balancer to shutdown.
String	toString()

Methods inherited from class io.grpc.LoadBalancer

acceptResolvedAddresses

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

ForwardingLoadBalancer

public ForwardingLoadBalancer()

Method Detail

delegate

protected abstract LoadBalancer delegate()

Returns the underlying balancer.

handleResolvedAddresses

public void handleResolvedAddresses(LoadBalancer.ResolvedAddresses resolvedAddresses)

Description copied from class: LoadBalancer

Handles newly resolved server groups and metadata attributes from name resolution system. servers contained in EquivalentAddressGroup should be considered equivalent but may be flattened into a single list if needed.

Implementations should not modify the given servers.

Overrides:

handleResolvedAddresses in class LoadBalancer

Parameters:

resolvedAddresses - the resolved server addresses, attributes, and config.

handleNameResolutionError

public void handleNameResolutionError(Status error)

Description copied from class: LoadBalancer

Handles an error from the name resolution system.

Specified by:

handleNameResolutionError in class LoadBalancer

Parameters:

error - a non-OK status

handleSubchannelState

@Deprecated
public void handleSubchannelState(LoadBalancer.Subchannel subchannel,
                                  ConnectivityStateInfo stateInfo)

Deprecated.

Description copied from class: LoadBalancer

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.

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.

Overrides:

handleSubchannelState in class LoadBalancer

Parameters:

subchannel - the involved Subchannel

stateInfo - the new state

shutdown

public void shutdown()

Description copied from class: LoadBalancer

The channel asks the load-balancer to shutdown. No more methods on this class will be called after this method. The implementation should shutdown all Subchannels and OOB channels, and do any other cleanup as necessary.

Specified by:

shutdown in class LoadBalancer

canHandleEmptyAddressListFromNameResolution

public boolean canHandleEmptyAddressListFromNameResolution()

Description copied from class: LoadBalancer

Whether this LoadBalancer can handle empty address group list to be passed to LoadBalancer.handleResolvedAddresses(ResolvedAddresses). The default implementation returns false, meaning that if the NameResolver returns an empty list, the Channel will turn that into an error and call LoadBalancer.handleNameResolutionError(io.grpc.Status). LoadBalancers that want to accept empty lists should override this method and return true.

This method should always return a constant value. It's not specified when this will be called.

Overrides:

canHandleEmptyAddressListFromNameResolution in class LoadBalancer

requestConnection

public void requestConnection()

Description copied from class: LoadBalancer

The channel asks the LoadBalancer to establish connections now (if applicable) so that the upcoming RPC may then just pick a ready connection without waiting for connections. This is triggered by ManagedChannel.getState(true).

If LoadBalancer doesn't override it, this is no-op. If it infeasible to create connections given the current state, e.g. no Subchannel has been created yet, LoadBalancer can ignore this request.

Overrides:

requestConnection in class LoadBalancer

toString

public String toString()

Overrides:

toString in class Object