org.tools4j.nobark.queue

Interface PollerListener<K,V>

Type Parameters:

K - the type of the conflation key

V - the type of values in the queue

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public interface PollerListener<K,V>

A listener for an poller of a ConflationQueue for instance useful to record performance metrics related to poll operations. The listener or a supplier thereof is usually passed to the constructor of a conflation queue. Note that listeners must be thread safe if used in a multi-consumer environment; best practice is to use separate listener instances for each consumer thread e.g. by using threadLocal(Supplier) or threadLocalSupplier(Supplier).

Field Summary

Fields

Modifier and Type	Field and Description
static PollerListener<java.lang.Object,java.lang.Object>	NOOP Constant for a no-op listener.

Method Summary

Modifier and Type	Method and Description
void	polled(ConflationQueue<? extends K,? extends V> queue, K key, V value) Called whenever a value is polled via any of the poll methods.
default void	polledButFoundEmpty(ConflationQueue<? extends K,? extends V> queue) Called whenever a poll attempt was made but the queue was found empty.
static <K,V> PollerListener<K,V>	threadLocal(java.util.function.Supplier<? extends PollerListener<K,V>> listenerSupplier) Creates a poller listener that delegates to thread-local listener instances created on demand by the given supplier.
static <L extends PollerListener<?,?>> java.util.function.Supplier<L>	threadLocalSupplier(java.util.function.Supplier<L> listenerSupplier) Creates a thread local supplier that creates a new instance once for every caller thread.

Field Detail

NOOP

static final PollerListener<java.lang.Object,java.lang.Object> NOOP

Constant for a no-op listener.

Method Detail

polled

void polled(ConflationQueue<? extends K,? extends V> queue,
            K key,
            V value)

Called whenever a value is polled via any of the poll methods. By default this method is also invoked when the queue was found empty (with null key and value) unless polledButFoundEmpty(ConflationQueue) is overridden and implemented differently.

Parameters:

queue - the conflation queue, sometimes useful to record queue size metrics, never null

key - the conflation key, may be null for poll invocations of the empty queue

value - the value that was polled, or null for unsuccessful poll invocations (i.e. when the queue was found empty)

polledButFoundEmpty

default void polledButFoundEmpty(ConflationQueue<? extends K,? extends V> queue)

Called whenever a poll attempt was made but the queue was found empty. The default implementation delegates the call to polled(ConflationQueue, Object, Object) passing nulls for key and value.

Parameters:

queue - the conflation queue, sometimes useful to record queue size metrics, never null

threadLocal

static <K,V> PollerListener<K,V> threadLocal(java.util.function.Supplier<? extends PollerListener<K,V>> listenerSupplier)

Creates a poller listener that delegates to thread-local listener instances created on demand by the given supplier. This listener can be passed to the constructors of AtomicConflationQueue which use a single poller instance for all consumer threads.

Type Parameters:

K - the type of the conflation key

V - the type of values in the queue

Parameters:

listenerSupplier - the supplier acting as factory for per-thread listener instances

Returns:

a listener that delegates to thread-local listener instances

threadLocalSupplier

static <L extends PollerListener<?,?>> java.util.function.Supplier<L> threadLocalSupplier(java.util.function.Supplier<L> listenerSupplier)

Creates a thread local supplier that creates a new instance once for every caller thread. This listener can be passed to the constructors of EvictConflationQueue and MergeConflationQueue which use a per thread poller instances; the returned supplier will create a new thread-local listener instance for every poller instance that is created.

Type Parameters:

L - the poller listener (sub-)type

Parameters:

listenerSupplier - the supplier acting as factory for per-thread listener instances

Returns:

a supplier creating thread-local listener instances