Package org.eclipse.aether.util.concurrency

Class ConcurrentWeakCache<K,​V>

  • Type Parameters:
    K - the type of keys
    V - the type of values
    public class ConcurrentWeakCache<K,​V>
extends java.lang.Object
    A concurrent cache with weak keys and weak values, inspired by maven-impl's Cache class but stripped down and optimized for hot-path performance.

    Design compared to the full Cache:

    • Zero allocation on get() — uses a ThreadLocal reusable lookup key instead of allocating a new wrapper on every read
    • O(1) cleanup per stale entry — uses identity-based removal from the ReferenceQueue instead of a full entrySet().removeIf() scan
    • Lock-free reads — ConcurrentHashMap.get(java.lang.Object) is a volatile read with no lock acquisition
    • Lock-striped writes — ConcurrentHashMap uses fine-grained locking

    Keys are held via WeakReference: when a key is no longer strongly referenced elsewhere, its entry becomes eligible for garbage collection. Values are also held via WeakReference. Stale entries are cleaned up lazily on put(K, V).

    Since:
    2.0.19

    • Constructor Summary

      Constructors 
      Constructor Description
      ConcurrentWeakCache()
      Creates a new cache with default initial capacity.
      ConcurrentWeakCache​(int initialCapacity)
      Creates a new cache with the given initial capacity.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      V get​(K key)
      Returns the value for the given key, or null if the key is not present or the value has been garbage collected.
      void put​(K key, V value)
      Stores a key-value pair in the cache.
      V putIfAbsent​(K key, V value)
      If the key is not already present (or its value has been GC'd), stores the key-value pair and returns the given value.
      int size()
      Returns the number of entries in the cache (including possibly stale ones).

      • Methods inherited from class java.lang.Object

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

    • Constructor Detail

      • ConcurrentWeakCache

        public ConcurrentWeakCache()
        Creates a new cache with default initial capacity.

      • ConcurrentWeakCache

        public ConcurrentWeakCache​(int initialCapacity)
        Creates a new cache with the given initial capacity.
        Parameters:
        initialCapacity - the initial capacity

    • Method Detail

      • get

        public V get​(K key)
        Returns the value for the given key, or null if the key is not present or the value has been garbage collected.

        This method is lock-free and allocates no objects.

        Parameters:
        key - the key to look up
        Returns:
        the cached value, or null

      • put

        public void put​(K key,
                V value)
        Stores a key-value pair in the cache. Both key and value are held via weak references.

        Also performs lazy cleanup of entries whose keys have been garbage collected.

        Parameters:
        key - the key
        value - the value

      • putIfAbsent

        public V putIfAbsent​(K key,
                     V value)
        If the key is not already present (or its value has been GC'd), stores the key-value pair and returns the given value. If the key is already present with a live value, returns the existing value without storing. Concurrent callers for the same key are guaranteed to receive the same instance (the insert-or-keep decision is atomic per key via ConcurrentHashMap.merge(K, V, java.util.function.BiFunction<? super V, ? super V, ? extends V>)).

        Also performs lazy cleanup of entries whose keys have been garbage collected.

        Parameters:
        key - the key
        value - the value to store if absent
        Returns:
        the existing value if present, or the given value if newly stored

      • size

        public int size()
        Returns the number of entries in the cache (including possibly stale ones).
        Returns:
        the cache size