org.tools4j.nobark.queue

Interface AppenderListener<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 AppenderListener<K,V>

A listener for an appender of a ConflationQueue for instance useful to record performance metrics related to enqueue 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-producer environment; best practice is to use separate listener instances for each producer thread e.g. by using threadLocal(Supplier) or threadLocalSupplier(Supplier).

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static class	AppenderListener.Conflation The type of conflation that occurred when an element was enqueued.

Field Summary

Fields

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

Method Summary

Modifier and Type	Method and Description
void	enqueued(ConflationQueue<? extends K,? extends V> queue, K key, V newValue, V oldValue, AppenderListener.Conflation conflation) Called whenever a value is enqueued.
static <K,V> AppenderListener<K,V>	threadLocal(java.util.function.Supplier<? extends AppenderListener<K,V>> listenerSupplier) Creates an appender listener that delegates to thread-local listener instances created on demand by the given supplier.
static <L extends AppenderListener<?,?>> 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 AppenderListener<java.lang.Object,java.lang.Object> NOOP

Constant for a no-op listener.

Method Detail

enqueued

void enqueued(ConflationQueue<? extends K,? extends V> queue,
              K key,
              V newValue,
              V oldValue,
              AppenderListener.Conflation conflation)

Called whenever a value is enqueued.

Parameters:

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

key - the conflation key, never null

newValue - the value that has been enqueued (the merged value if conflation==MERGED), never null

oldValue - the old value that is replaced, unless conflation=UNCONFLATED in which case old value is either null or the exchange value in case of an ExchangeConflationQueue

conflation - the type of conflation that has occurred, if any

threadLocal

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

Creates an appender 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 appender instance for all producer 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 AppenderListener<?,?>> 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 appender instances; the returned supplier will create a new thread-local listener instance for every appender instance that is created.

Type Parameters:

L - the appender listener (sub-)type

Parameters:

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

Returns:

a supplier creating thread-local listener instances