/// <summary>
/// Sets the specific value for the specified key.
/// </summary>
/// <param name="key">The key for which value needs to be set.</param>
/// <param name="value">The value to be set.</param>
public void Set(TKey key, TValue value)
{
if (key == null)
{
throw new ArgumentNullException($"'{nameof(key)}' cannot be null.");
}
lock (_lock)
{
if (_dictionary.TryGetValue(
key: key,
value: out LRUChainItem <KeyValuePair <TKey, TValue> > lruChainItem)) // Key already present in cache.
{
// Promote the LRU chain item and update the value in the chain item.
lruChainItem.ItemValue = new KeyValuePair <TKey, TValue>(key, value);
_lruChain.Promote(lruChainItem);
}
else // Key does not exist in the cache. Add fresh.
{
// See if eviction is required.
EvictIfRequired();
// Set the item in the cache.
lruChainItem = new LRUChainItem <KeyValuePair <TKey, TValue> >(new KeyValuePair <TKey, TValue>(key, value));
_dictionary[key] = lruChainItem;
_lruChain.AddFirst(lruChainItem);
}
}
}
/// <summary>
/// Adds item to the front of the list.
/// </summary>
public void AddFirst(LRUChainItem <TValue> item)
{
if (item == null)
{
throw new ArgumentNullException($"'{nameof(item)}' cannot be null");
}
if (_head == null) // case of empty list
{
item.Previous = null;
item.Next = null;
_head = item;
_tail = item;
}
else
{
// Create a link between the item and _head.
item.Previous = null;
item.Next = _head;
_head.Previous = item;
_head = item;
// Tail doesn't update.
}
}
/// <summary>
/// Removes the specified item.
/// </summary>
public void Remove(LRUChainItem <TValue> item)
{
if (item == null)
{
throw new ArgumentNullException($"'{nameof(item)}' cannot be null");
}
// Update the link between the previous and next items.
if (item.Previous != null)
{
item.Previous.Next = item.Next;
}
if (item.Next != null)
{
item.Next.Previous = item.Previous;
}
// Check if _tail needs to be updated.
if (_tail == item)
{
_tail = item.Previous;
}
// Check if _head needs to be updated.
if (_head == item)
{
_head = item.Next;
}
}
/// <summary>
/// Promotes the item to the front of the list.
/// </summary>
public void Promote(LRUChainItem <TValue> item)
{
if (item == null)
{
throw new ArgumentNullException($"'{nameof(item)}' cannot be null");
}
if (item == _head)
{
// Already at the front of the list. No action requried.
return;
}
Remove(item);
AddFirst(item);
}