net.openhft.chronicle.core.threads

Class ThreadLocalHelper

java.lang.Object

net.openhft.chronicle.core.threads.ThreadLocalHelper

public final class ThreadLocalHelper
extends Object

Utility methods for caching values in a ThreadLocal without locking.

Each thread keeps its own instance so no synchronisation is required. Where WeakReferences are used the value can be reclaimed once nothing else refers to it, preventing user-level leaks if the thread outlives the value.

Method Summary

Modifier and Type	Method and Description
static <T> T	getSTL(@NotNull ThreadLocal<T> threadLocal, @NotNull Supplier<T> supplier) Gets a strong thread-local value without needing locks.
static <T,A> T	getTL(@NotNull ThreadLocal<WeakReference<T>> threadLocal, A a, @NotNull Function<A,T> function) Gets a thread-local value via a function using a WeakReference.
static <T,A> T	getTL(@NotNull ThreadLocal<WeakReference<T>> threadLocal, A supplyingEntity, @NotNull Function<A,T> constructor, @Nullable ReferenceQueue<T> referenceQueue, @Nullable Consumer<WeakReference<T>> registrar) Gets a thread-local value via a function and records the weak reference.
static <T> T	getTL(@NotNull ThreadLocal<WeakReference<T>> threadLocal, @NotNull Supplier<T> supplier) Gets a thread-local value backed by a WeakReference without locks.

Methods inherited from class java.lang.Object

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

Method Detail

getTL

@NotNull
public static <T> T getTL(@NotNull
                                   @NotNull ThreadLocal<WeakReference<T>> threadLocal,
                                   @NotNull
                                   @NotNull Supplier<T> supplier)

Gets a thread-local value backed by a WeakReference without locks.

The value is created via the supplier when absent. Storing the weak reference means it can be cleared when the caller drops the strong reference, avoiding memory leaks if the thread persists.

Type Parameters:

T - Type of value held

Parameters:

threadLocal - ThreadLocal storing the weak reference

supplier - Supplier used to create the value on first access

Returns:

Existing or newly created value

getSTL

@NotNull
public static <T> T getSTL(@NotNull
                                    @NotNull ThreadLocal<T> threadLocal,
                                    @NotNull
                                    @NotNull Supplier<T> supplier)

Gets a strong thread-local value without needing locks.

The supplier is called once per thread to create the value. The returned object remains strongly referenced by the thread until removed, so use getTL(ThreadLocal, Supplier) if the value should be reclaimable.

Type Parameters:

T - Type of value held

Parameters:

threadLocal - ThreadLocal holding the value

supplier - Supplier used to create the value when absent

Returns:

Existing or newly created value

getTL

@NotNull
public static <T,A> T getTL(@NotNull
                                     @NotNull ThreadLocal<WeakReference<T>> threadLocal,
                                     A a,
                                     @NotNull
                                     @NotNull Function<A,T> function)

Gets a thread-local value via a function using a WeakReference.

Each thread holds its own instance so no locking is needed. The supplier is invoked only when the reference is absent or has been cleared.

Type Parameters:

T - Type of value held

A - Type of the supplied argument

Parameters:

threadLocal - ThreadLocal storing the weak reference

a - Input passed to the constructor function

function - Function used to create the value when required

Returns:

Existing or newly created value

getTL

@NotNull
public static <T,A> T getTL(@NotNull
                                     @NotNull ThreadLocal<WeakReference<T>> threadLocal,
                                     @NotNull
                                     A supplyingEntity,
                                     @NotNull
                                     @NotNull Function<A,T> constructor,
                                     @Nullable
                                     @Nullable ReferenceQueue<T> referenceQueue,
                                     @Nullable
                                     @Nullable Consumer<WeakReference<T>> registrar)

Gets a thread-local value via a function and records the weak reference.

When a new value is created the reference may be registered in the given referenceQueue using the supplied registrar. This lets a background cleaner notice when the value has been cleared and remove any associated state outside the event loop.

Type Parameters:

T - Type of value held

A - Type of the supplied argument

Parameters:

threadLocal - ThreadLocal holding the weak reference

supplyingEntity - Argument passed to the constructor

constructor - Function to create the value if required

referenceQueue - Optional queue in which to enqueue the weak reference

registrar - Optional consumer used to register the reference

Returns:

Existing or newly created value