Package io.servicetalk.loadbalancer

Class RoundRobinLoadBalancer<ResolvedAddress,C extends LoadBalancedConnection>

java.lang.Object

io.servicetalk.loadbalancer.RoundRobinLoadBalancer<ResolvedAddress,C>

Type Parameters:

ResolvedAddress - The resolved address type.

C - The type of connection.

All Implemented Interfaces:

LoadBalancer<C>, AsyncCloseable, ListenableAsyncCloseable

public final class RoundRobinLoadBalancer<ResolvedAddress,C extends LoadBalancedConnection>
extends java.lang.Object
implements LoadBalancer<C>

A LoadBalancer that uses a round robin strategy for selecting addresses. It has the following behaviour:

• Round robining is done at address level.
• Connections are created lazily, without any concurrency control on their creation. This can lead to over-provisioning connections when dealing with a requests surge.
• Existing connections are reused unless a selector passed to selectConnection(Predicate) suggests otherwise. This can lead to situations where connections will be used to their maximum capacity (for example in the context of pipelining) before new connections are created.
• Closed connections are automatically pruned.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	RoundRobinLoadBalancer.RoundRobinLoadBalancerFactory<ResolvedAddress,C extends LoadBalancedConnection>	LoadBalancerFactory for RoundRobinLoadBalancer.

Constructor Summary

Constructors

Constructor	Description
RoundRobinLoadBalancer(Publisher<? extends ServiceDiscovererEvent<ResolvedAddress>> eventPublisher, ConnectionFactory<ResolvedAddress,? extends C> connectionFactory)	Creates a new instance.

Method Summary

Modifier and Type	Method	Description
Completable	closeAsync()	Used to close/shutdown a resource.
Completable	closeAsyncGracefully()	Used to close/shutdown a resource, similar to AsyncCloseable.closeAsync(), but attempts to cleanup state before abruptly closing.
Publisher<java.lang.Object>	eventStream()	A Publisher of events provided by this LoadBalancer.
static <ResolvedAddress,C extends LoadBalancedConnection> RoundRobinLoadBalancer.RoundRobinLoadBalancerFactory<ResolvedAddress,C>	newRoundRobinFactory()	Create a LoadBalancerFactory that creates instances of RoundRobinLoadBalancer.
Completable	onClose()	Returns a Completable that is notified once the ListenableAsyncCloseable was closed.
Single<C>	selectConnection(java.util.function.Predicate<C> selector)	Select the most appropriate connection for a request.

Methods inherited from class java.lang.Object

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

Constructor Detail

RoundRobinLoadBalancer

public RoundRobinLoadBalancer(Publisher<? extends ServiceDiscovererEvent<ResolvedAddress>> eventPublisher,
                              ConnectionFactory<ResolvedAddress,? extends C> connectionFactory)

Creates a new instance.

Parameters:

eventPublisher - provides a stream of addresses to connect to.

connectionFactory - a function which creates new connections.

Method Detail

newRoundRobinFactory

public static <ResolvedAddress,C extends LoadBalancedConnection> RoundRobinLoadBalancer.RoundRobinLoadBalancerFactory<ResolvedAddress,C> newRoundRobinFactory()

Create a LoadBalancerFactory that creates instances of RoundRobinLoadBalancer.

Type Parameters:

ResolvedAddress - The resolved address type.

C - The type of connection.

Returns:

a LoadBalancerFactory that creates instances of RoundRobinLoadBalancer.

selectConnection

public Single<C> selectConnection(java.util.function.Predicate<C> selector)

Description copied from interface: LoadBalancer

Select the most appropriate connection for a request. Returned connection may be used concurrently for other requests.

Specified by:

selectConnection in interface LoadBalancer<ResolvedAddress>

Parameters:

selector - A Function that evaluates a connection for selection. This selector should return null if the connection MUST not be selected. This selector is guaranteed to be called for any connection that is returned from this method.

Returns:

a Single that completes with the most appropriate connection to use.

eventStream

public Publisher<java.lang.Object> eventStream()

Description copied from interface: LoadBalancer

A Publisher of events provided by this LoadBalancer. This maybe used to broadcast internal state of this LoadBalancer to provide hints/visibility for external usage.

Specified by:

eventStream in interface LoadBalancer<ResolvedAddress>

Returns:

A Publisher of events provided by this LoadBalancer.

onClose

public Completable onClose()

Description copied from interface: ListenableAsyncCloseable

Returns a Completable that is notified once the ListenableAsyncCloseable was closed.

Specified by:

onClose in interface ListenableAsyncCloseable

Returns:

the Completable that is notified on close.

closeAsync

public Completable closeAsync()

Description copied from interface: AsyncCloseable

Used to close/shutdown a resource.

Specified by:

closeAsync in interface AsyncCloseable

Returns:

A Completable that is notified once the close is complete.

closeAsyncGracefully

public Completable closeAsyncGracefully()

Description copied from interface: AsyncCloseable

Used to close/shutdown a resource, similar to AsyncCloseable.closeAsync(), but attempts to cleanup state before abruptly closing. This provides a hint that implementations can use to stop accepting new work and finish in flight work. This method is implemented on a "best effort" basis and may be equivalent to AsyncCloseable.closeAsync().

Note: Implementations may or may not apply a timeout for this operation to complete, if a caller does not want to wait indefinitely, and are unsure if the implementation applies a timeout, it is advisable to apply a timeout and force a call to AsyncCloseable.closeAsync().

Specified by:

closeAsyncGracefully in interface AsyncCloseable

Returns:

A Completable that is notified once the close is complete.