CacheTKey, TValue Class

Represents a generic cache. If an item loader is specified, then cache expansion is transparent: the user needs only to read the indexer to retrieve items. When a non-existing key is accessed, then the item is loaded automatically by the loader function that was passed to the constructor. If the cache is full (elements Count reaches the Capacity) and a new element has to be stored, then the oldest or least recent used element (depends on the value of Behavior) is removed from the cache.

Definition

Namespace: KGySoft.Collections
Assembly: KGySoft.CoreLibraries (in KGySoft.CoreLibraries.dll) Version: 7.0.0
C#
[SerializableAttribute]
public class Cache<TKey, TValue> : IDictionary<TKey, TValue>, 
	ICollection<KeyValuePair<TKey, TValue>>, IEnumerable<KeyValuePair<TKey, TValue>>, 
	IEnumerable, ICache, IDictionary, ICollection, ISerializable, 
	IDeserializationCallback, IReadOnlyDictionary<TKey, TValue>, IReadOnlyCollection<KeyValuePair<TKey, TValue>>
Inheritance
Object    CacheTKey, TValue
Implements
ICache, ICollectionKeyValuePairTKey, TValue, IDictionaryTKey, TValue, IEnumerableKeyValuePairTKey, TValue, IReadOnlyCollectionKeyValuePairTKey, TValue, IReadOnlyDictionaryTKey, TValue, ICollection, IDictionary, IEnumerable, IDeserializationCallback, ISerializable

Type Parameters

TKey
Type of the keys stored in the cache.
TValue
Type of the values stored in the cache.

Remarks

CacheTKey, TValue type provides a fast-access storage with limited capacity and transparent access. If you need to store items that are expensive to retrieve (for example from a database or remote service) and you don't want to run out of memory because of just storing newer and newer elements without getting rid of old ones, then this type might fit your expectations. Once a value is stored in the cache, its retrieval by using its key is very fast, close to O(1).

A cache store must meet the following three criteria:

  1. Associative access – Accessing elements works the same way as in case of the DictionaryTKey, TValue type. CacheTKey, TValue implements both the generic IDictionaryTKey, TValue and the non-generic IDictionary interfaces so can be used similarly as DictionaryTKey, TValue or Hashtable types.
  2. Transparency – Users of the cache need only to read the cache by its indexer property. If needed, elements will be automatically loaded on the first access.
  3. Size managementCacheTKey, TValue type has a Capacity, which is the allowed maximal elements count. If the cache is full, the oldest or least recent used element will be automatically removed from the cache (see Behavior property).

Since CacheTKey, TValue implements IDictionaryTKey, TValue interface, Add, Remove, ContainsKey and TryGetValue methods are available for it, and these methods work exactly the same way as in case the DictionaryTKey, TValue type. But using these methods usually are not necessary, unless we want to manually manage cache content or when cache is initialized without an item loader. Normally after cache is instantiated, it is needed to be accessed only by the getter accessor of its indexer.

  Caution

Serializing a cache instance by IFormatter implementations involves the serialization of the item loader delegate. To deserialize a cache the assembly of the loader must be accessible. If you need to serialize cache instances try to use static methods as data loaders and avoid using anonymous delegates or lambda expressions, otherwise it is not guaranteed that another implementations or versions of CLR will able to deserialize data and resolve the compiler-generated members.

  Caution

.NET Core does not support serializing delegates. If the CacheTKey, TValue instance was initialized by a loader delegate it is possible that serialization throws a SerializationException on some platforms.

Example

The following example shows the suggested usage of CacheTKey, TValue.
C#
using System;
using System.Collections.Generic;
using KGySoft.Collections;

class Example
{
    private static Cache<int, bool> isPrimeCache;

    public static void Main()
    {
        // Cache capacity is initialized to store maximum 4 values
        isPrimeCache = new Cache<int, bool>(ItemLoader, 4);

        // If cache is full the least recent used element will be deleted
        isPrimeCache.Behavior = CacheBehavior.RemoveLeastRecentUsedElement;

        // cache is now empty
        DumpCache();

        // reading the cache invokes the loader method
        CheckPrime(13);

        // reading a few more values
        CheckPrime(23);
        CheckPrime(33);
        CheckPrime(43);

        // dumping content
        DumpCache();

        // accessing an already read item does not invoke loader again
        // Now it changes cache order because of the chosen behavior
        CheckPrime(13);
        DumpCache();

        // reading a new element with full cache will delete an old one (now 23)
        CheckPrime(111);
        DumpCache();

        // but accessing a deleted element causes to load it again
        CheckPrime(23);
        DumpCache();

        // dumping some statistics
        Console.WriteLine(isPrimeCache.GetStatistics().ToString());
    }

    // This is the item loader method. It can access database or perform slow calculations.
    // If cache is meant to be serialized it should be a static method rather than an anonymous delegate or lambda expression.
    private static bool ItemLoader(int number)
    {
        Console.WriteLine("Item loading has been invoked for value {0}", number);

        // In this example item loader checks whether the given number is a prime by a not too efficient algorithm.
        if (number <= 1)
            return false;
        if (number % 2 == 0)
            return true;
        int i = 3;
        int sqrt = (int)Math.Floor(Math.Sqrt(number));
        while (i <= sqrt)
        {
            if (number % i == 0)
                return false;
            i += 2;
        }

        return true;
    }

    private static void CheckPrime(int number)
    {
        // cache is used transparently here: indexer is always just read
        bool isPrime = isPrimeCache[number];
        Console.WriteLine("{0} is a prime: {1}", number, isPrime);
    }

    private static void DumpCache()
    {
        Console.WriteLine();
        Console.WriteLine("Cache elements count: {0}", isPrimeCache.Count);
        if (isPrimeCache.Count > 0)
        {
            // enumerating through the cache shows the elements in the evaluation order
            Console.WriteLine("Cache elements:");
            foreach (KeyValuePair<int, bool> item in isPrimeCache)
            {
                Console.WriteLine("\tKey: {0},\tValue: {1}", item.Key, item.Value);
            }
        }

        Console.WriteLine();
    }
}

// This code example produces the following output:
//
// Cache elements count: 0
// 
// Item loading has been invoked for value 13
// 13 is a prime: True
// Item loading has been invoked for value 23
// 23 is a prime: True
// Item loading has been invoked for value 33
// 33 is a prime: False
// Item loading has been invoked for value 43
// 43 is a prime: True
// 
// Cache elements count: 4
// Cache elements:
// Key: 13,        Value: True
// Key: 23,        Value: True
// Key: 33,        Value: False
// Key: 43,        Value: True
// 
// 13 is a prime: True
// 
// Cache elements count: 4
// Cache elements:
// Key: 23,        Value: True
// Key: 33,        Value: False
// Key: 43,        Value: True
// Key: 13,        Value: True
// 
// Item loading has been invoked for value 111
// 111 is a prime: False
// 
// Cache elements count: 4
// Cache elements:
// Key: 33,        Value: False
// Key: 43,        Value: True
// Key: 13,        Value: True
// Key: 111,       Value: False
// 
// Item loading has been invoked for value 23
// 23 is a prime: True
// 
// Cache elements count: 4
// Cache elements:
// Key: 43,        Value: True
// Key: 13,        Value: True
// Key: 111,       Value: False
// Key: 23,        Value: True
// 
// Cache<Int32, Boolean> cache statistics:
// Count: 4
// Capacity: 4
// Number of writes: 6
// Number of reads: 7
// Number of cache hits: 1
// Number of deletes: 2
// Hit rate: 14,29%

Constructors

CacheTKey, TValue Initializes a new instance of the CacheTKey, TValue class with default capacity of 128 and no item loader.
CacheTKey, TValue(IEqualityComparerTKey) Initializes a new instance of the CacheTKey, TValue class with the specified comparer, default capacity of 128 and no item loader.
CacheTKey, TValue(FuncTKey, TValue, IEqualityComparerTKey) Creates a new CacheTKey, TValue instance with the given itemLoader and comparer using default capacity of 128.
CacheTKey, TValue(IDictionaryTKey, TValue, IEqualityComparerTKey) Initializes a new instance of the CacheTKey, TValue class from the specified dictionary and comparer, with no item loader. The Capacity will be initialized to the number of elements in dictionary.
CacheTKey, TValue(Int32, IEqualityComparerTKey) Initializes a new instance of the CacheTKey, TValue class with specified capacity capacity and comparer and no item loader.
CacheTKey, TValue(SerializationInfo, StreamingContext) Initializes a new instance of the CacheTKey, TValue class from serialized data.
CacheTKey, TValue(FuncTKey, TValue, Int32, IEqualityComparerTKey) Creates a new CacheTKey, TValue instance with the given itemLoader, capacity and comparer.

Properties

Behavior Gets or sets the cache behavior when cache is full and an element has to be removed. The cache is full, when Count reaches the Capacity. Default value: RemoveLeastRecentUsedElement.
Capacity Gets or sets the capacity of the cache. If new value is smaller than elements count (value of the Count property), then old or least used elements (depending on Behavior) will be removed from CacheTKey, TValue.
Default value: 128, if the CacheTKey, TValue was initialized without specifying a capacity; otherwise, as it was initialized.
Count Gets number of elements currently stored in this CacheTKey, TValue instance.
DisposeDroppedValues Gets or sets whether internally dropped values are disposed if they implement IDisposable.
Default value: .
EnsureCapacity Gets or sets whether adding the first item to the cache or resetting Capacity on a non-empty cache should allocate memory for all cache entries.
Default value: , unless you use the IDictionaryTKey, TValue initializer constructor, which initializes this property to .
Item Gets or sets the value associated with the specified key. When an element with a non-existing key is read, and an item loader was specified by the appropriate constructor, then the value is retrieved by the specified loader delegate of this CacheTKey, TValue instance.
Keys Gets the keys stored in the cache in evaluation order.
Values Gets the values stored in the cache in evaluation order.

Methods

Add Adds an element with the provided key and value to the CacheTKey, TValue.
Clear Removes all keys and values from the CacheTKey, TValue.
ContainsKey Determines whether the CacheTKey, TValue contains a specific key.
ContainsValue Determines whether the CacheTKey, TValue contains a specific value.
GetEnumerator Returns an enumerator that iterates through the CacheTKey, TValue elements in the evaluation order.
GetObjectData In a derived class populates a SerializationInfo with the additional data of the derived type needed to serialize the target object.
GetStatistics Gets an ICacheStatistics instance that provides statistical information about this CacheTKey, TValue.
GetThreadSafeAccessor Gets a thread safe accessor for this CacheTKey, TValue instance. As it provides only a single readable indexer, it makes sense only if an item loader was passed to the appropriate constructor and the cache will not be accessed by other members but via the returned accessor.
GetValueUncached Loads the value of the key even if it already exists in the CacheTKey, TValue by using the item loader that was passed to the constructor.
OnDeserialization In a derived class restores the state the deserialized instance.
RefreshValue Refreshes the value of the key in the CacheTKey, TValue even if it already exists in the cache by using the item loader that was passed to the constructor.
Remove Removes the value with the specified key from the CacheTKey, TValue.
Reset Clears the CacheTKey, TValue and resets statistics.
Touch Renews the value with the specified key in the evaluation order.
TryGetValue Tries to gets the value associated with the specified key without using the item loader passed to the constructor.

Extension Methods

AddRangeKeyValuePairTKey, TValue Adds a collection to the target ICollectionT.
(Defined by CollectionExtensions)
AsThreadSafeKeyValuePairTKey, TValue Returns a LockingCollectionT, which provides a thread-safe wrapper for the specified collection. This only means that if the members are accessed through the returned LockingCollectionT, then the inner state of the wrapped collection remains always consistent and not that all of the multi-threading concerns can be ignored.
See the Remarks section of the LockingCollectionT class for details and some examples.
(Defined by CollectionExtensions)
Convert Converts an Object specified in the obj parameter to the desired targetType.
See the Examples section of the generic ConvertTTarget(Object, CultureInfo) overload for an example.
(Defined by ObjectExtensions)
ConvertTTarget Converts an Object specified in the obj parameter to the desired TTarget.
(Defined by ObjectExtensions)
ForEachKeyValuePairTKey, TValue Similarly to the List<T>.ForEach method, processes an action on each element of an enumerable collection.
(Defined by EnumerableExtensions)
GetRandomElementKeyValuePairTKey, TValue Gets a random element from the enumerable source using a new FastRandom instance.
(Defined by EnumerableExtensions)
GetRandomElementKeyValuePairTKey, TValue Gets a random element from the enumerable source using a specified Random instance.
(Defined by EnumerableExtensions)
In Gets whether item is among the elements of set.
See the Examples section of the generic InT(T, T) overload for an example.
(Defined by ObjectExtensions)
IndexOf Searches for an element in the source enumeration where the specified predicate returns .
(Defined by EnumerableExtensions)
IndexOf Searches for an element in the source enumeration.
(Defined by EnumerableExtensions)
IndexOfKeyValuePairTKey, TValue Searches for an element in the source enumeration where the specified predicate returns .
(Defined by EnumerableExtensions)
IndexOfKeyValuePairTKey, TValue Searches for an element in the source enumeration.
(Defined by EnumerableExtensions)
IsNullOrEmpty Determines whether the specified source is or empty (has no elements).
(Defined by EnumerableExtensions)
IsNullOrEmptyKeyValuePairTKey, TValue Determines whether the specified source is or empty (has no elements).
(Defined by EnumerableExtensions)
JoinKeyValuePairTKey, TValue Concatenates the items of the source collection into a new string instance using the specified separator between the items.
(Defined by EnumerableExtensions)
JoinKeyValuePairTKey, TValue Concatenates the items of the source collection into a new string instance using the specified separator between the items.
(Defined by EnumerableExtensions)
ShuffleKeyValuePairTKey, TValue Shuffles an enumerable source (randomizes its elements) using a new FastRandom instance.
(Defined by EnumerableExtensions)
ShuffleKeyValuePairTKey, TValue Shuffles an enumerable source (randomizes its elements) using the provided seed with a new FastRandom instance.
(Defined by EnumerableExtensions)
ShuffleKeyValuePairTKey, TValue Shuffles an enumerable source (randomizes its elements) using the provided seed with a new FastRandom instance.
(Defined by EnumerableExtensions)
ShuffleKeyValuePairTKey, TValue Shuffles an enumerable source (randomizes its elements) using a specified Random instance.
(Defined by EnumerableExtensions)
ToCircularListKeyValuePairTKey, TValue Creates a CircularListT from an IEnumerableT.
(Defined by EnumerableExtensions)
ToStringKeyedDictionaryKeyValuePairTKey, TValue Creates a StringKeyedDictionaryTValue from an IEnumerableT instance using the specified keySelector delegate and a comparer.
(Defined by EnumerableExtensions)
ToStringKeyedDictionaryKeyValuePairTKey, TValue, TValue Creates a StringKeyedDictionaryTValue from an IEnumerableT instance using the specified key and value selector delegates and a comparer.
(Defined by EnumerableExtensions)
TryAdd Tries to add the specified item to the collection.
(Defined by EnumerableExtensions)
TryAddKeyValuePairTKey, TValue Tries to add the specified item to the collection.
(Defined by EnumerableExtensions)
TryAddRange Tries to add the specified collection to the target collection.
(Defined by EnumerableExtensions)
TryAddRangeKeyValuePairTKey, TValue Tries to add the specified collection to the target collection.
(Defined by EnumerableExtensions)
TryClear Tries to remove all elements from the collection.
(Defined by EnumerableExtensions)
TryClearKeyValuePairTKey, TValue Tries to remove all elements from the collection.
(Defined by EnumerableExtensions)
TryConvert Tries to convert an Object specified in the obj parameter to the desired targetType.
See the Examples section of the ConvertTTarget(Object, CultureInfo) method for a related example.
(Defined by ObjectExtensions)
TryConvert Tries to convert an Object specified in the obj parameter to the desired targetType.
See the Examples section of the ConvertTTarget(Object, CultureInfo) method for a related example.
(Defined by ObjectExtensions)
TryConvertTTarget Tries to convert an Object specified in the obj parameter to the desired TTarget.
See the Examples section of the ConvertTTarget(Object, CultureInfo) method for a related example.
(Defined by ObjectExtensions)
TryConvertTTarget Tries to convert an Object specified in the obj parameter to the desired TTarget.
See the Examples section of the ConvertTTarget(Object, CultureInfo) method for a related example.
(Defined by ObjectExtensions)
TryGetCount Tries to get the number of elements in the source enumeration without enumerating it.
(Defined by EnumerableExtensions)
TryGetCountKeyValuePairTKey, TValue Tries to get the number of elements in the source enumeration without enumerating it.
(Defined by EnumerableExtensions)
TryGetElementAt Tries to get an item at the specified index in the collection.
(Defined by EnumerableExtensions)
TryGetElementAtKeyValuePairTKey, TValue Tries to get an item at the specified index in the collection.
(Defined by EnumerableExtensions)
TryInsert Tries to insert the specified item at the specified index to the collection.
(Defined by EnumerableExtensions)
TryInsertKeyValuePairTKey, TValue Tries to insert the specified item at the specified index to the collection.
(Defined by EnumerableExtensions)
TryInsertRange Tries to insert the specified collection into the target collection.
(Defined by EnumerableExtensions)
TryInsertRangeKeyValuePairTKey, TValue Tries to insert the specified collection into the target collection.
(Defined by EnumerableExtensions)
TryRemove Tries to remove the specified item from to the collection.
(Defined by EnumerableExtensions)
TryRemoveKeyValuePairTKey, TValue Tries to remove the specified item from to the collection.
(Defined by EnumerableExtensions)
TryRemoveAt Tries to remove an item at the specified index from the collection.
(Defined by EnumerableExtensions)
TryRemoveAtKeyValuePairTKey, TValue Tries to remove an item at the specified index from the collection.
(Defined by EnumerableExtensions)
TryRemoveRange Tries to remove count amount of items from the specified collection at the specified index.
(Defined by EnumerableExtensions)
TryRemoveRangeKeyValuePairTKey, TValue Tries to remove count amount of items from the specified collection at the specified index.
(Defined by EnumerableExtensions)
TryReplaceRange Tries to remove count amount of items from the target at the specified index, and to insert the specified collection at the same position. The number of elements in collection can be different from the amount of removed items.
(Defined by EnumerableExtensions)
TryReplaceRangeKeyValuePairTKey, TValue Tries to remove count amount of items from the target at the specified index, and to insert the specified collection at the same position. The number of elements in collection can be different from the amount of removed items.
(Defined by EnumerableExtensions)
TrySetElementAt Tries to set the specified item at the specified index in the collection.
(Defined by EnumerableExtensions)
TrySetElementAtKeyValuePairTKey, TValue Tries to set the specified item at the specified index in the collection.
(Defined by EnumerableExtensions)

Thread Safety

Members of this type are not safe for multi-threaded operations, though a thread-safe accessor can be obtained for the CacheTKey, TValue by the GetThreadSafeAccessor method. To get a thread-safe wrapper for all members use the AsThreadSafe extension method instead.

  Note

If a CacheTKey, TValue instance is wrapped into a LockingDictionaryTKey, TValue instance, then the whole cache will be locked during the time when the item loader delegate is being called. If that is not desirable consider to use the GetThreadSafeAccessor method instead with the default arguments and access the cache only via the returned accessor.

See Also