Interface StateStore

All Known Implementing Classes:

MemoryStateStore

public interface StateStore

Interface for a simple KV state store

Method Summary

Modifier and Type	Method	Description
default double	add(String key, double delta)
void	clear()
default void	clear(String key)
default int	dec(String key)
default com.google.common.util.concurrent.AtomicDouble	getAccumulator(String key)	Returns the AtomicDouble accumulator for the given key, creating it lazily on first access.
default AtomicInteger	getCounter(String key)	Returns the AtomicInteger counter for the given key, creating it lazily on first access.
default <T> T	getOrCreateState(String key, Supplier<T> factory)	Returns the value for the given key, creating and storing it via factory on first access.
<T> T	getState(String key)
default <T> T	getState(String key, T defaultValue)
default boolean	has(String key)
default int	inc(String key)
default boolean	is(String key)
default void	reset(String key)	Resets the value at the given key based on its type: AtomicInteger and AtomicDouble are set to 0, Boolean values are unset (set to false).
default void	set(String key)
default void	set(String key, boolean value)
<T> void	setState(String key, T value)
default void	unset(String key)

Method Details

setState

<T> void setState(String key,
 T value)

getState

<T> T getState(String key)

getState

default <T> T getState(String key,
 T defaultValue)

clear

void clear()

has

default boolean has(String key)

clear

default void clear(String key)

inc

default int inc(String key)

dec

default int dec(String key)

add

default double add(String key,
 double delta)

reset

default void reset(String key)

Resets the value at the given key based on its type: AtomicInteger and AtomicDouble are set to 0, Boolean values are unset (set to false). Other types are left unchanged. This polymorphic reset avoids removing the entry, preserving the type for future use.

Parameters:

key - the state key to reset

set

default void set(String key)

unset

default void unset(String key)

set

default void set(String key,
 boolean value)

is

default boolean is(String key)

getOrCreateState

default <T> T getOrCreateState(String key,
 Supplier<T> factory)

Returns the value for the given key, creating and storing it via factory on first access. This is the lazy-creation seam behind getCounter(String)/getAccumulator(String): the atomicity of those accessors' thread-safety promise is only as strong as this method.

This DEFAULT implementation is check-then-put and therefore NOT atomic — two concurrent first accesses can each create a value and one wins, so increments applied to the loser are lost. Implementations backed by a concurrent map MUST override it with an atomic compute-if-absent (see MemoryStateStore); only single-threaded stores may keep the default.

Parameters:

key - the state key

factory - creates the value when absent

Returns:

the stored value (never null)

getCounter

default AtomicInteger getCounter(String key)

Returns the AtomicInteger counter for the given key, creating it lazily on first access. Thread-safe for concurrent increment/decrement operations WHEN the implementation provides an atomic getOrCreateState(String, Supplier) — the historical inline check-then-put here could hand two racing threads two different counters, silently losing increments.

Parameters:

key - the state key

Returns:

the atomic counter (never null)

getAccumulator

default com.google.common.util.concurrent.AtomicDouble getAccumulator(String key)

Returns the AtomicDouble accumulator for the given key, creating it lazily on first access. Thread-safe for concurrent add operations under the same getOrCreateState(String, Supplier) atomicity condition as getCounter(String).

Parameters:

key - the state key

Returns:

the atomic accumulator (never null)