private void RemoveFromLinkedList(LeastRecentlyUsedCacheNode node)
{
var nextNode = node.Next;
var prevNode = node.Previous;
if (nextNode != null)
{
//move next node's previous to original node's previous
nextNode.Previous = node.Previous;
}
if (prevNode != null)
{
//move previous node's next to original node's previous
prevNode.Next = node.Next;
}
if (_head == node)
{
_head = nextNode;
}
if (_tail == node)
{
_tail = prevNode;
}
}
private void MakeMostRecentlyUsed(LeastRecentlyUsedCacheNode node)
{
if (node == _head)
{
return;
}
RemoveFromLinkedList(node);
AddToHead(node);
}
/// <summary>
/// Removes all items from the cache.
/// </summary>
public void Clear()
{
using (_entriesSync.WriteLock())
{
_nodesByKey.Clear();
_head = null;
_tail = null;
_currentCount = 0;
}
}
private void AddToHead(LeastRecentlyUsedCacheNode node)
{
node.Previous = null;
node.Next = _head;
if (_head != null)
{
_head.Previous = node;
}
_head = node;
}
/// <summary>
/// Inserts a specified key and value into the cache.
/// </summary>
/// <param name="key">The key to add.</param>
/// <param name="value">The value to add.</param>
/// <remarks>
/// Internall this method will :
/// 1) If the cache is full, remove the LRU item from the cache.
/// 2) If the specified key already exists in the cache, update the value held in the cache.
/// 3) Mark the key/value added as the new LRU item in the cache.
/// </remarks>
/// <exception cref="ArgumentNullException"><paramref name="key"/> was null.</exception>
public void Insert(TKey key, TValue value)
{
if (key == null)
{
throw new ArgumentNullException(nameof(key),
$"Unable to insert into MRU Cache. {nameof(key)} parameter cannot be null");
}
using (_entriesSync.WriteLock())
{
LeastRecentlyUsedCacheNode node;
if (!_nodesByKey.TryGetValue(key, out node))
{
//not in cache so insert
//check another thread has not inserted the node
if (!_nodesByKey.TryGetValue(key, out node))
{
if (IsFull)
{
node = _tail;
_nodesByKey.Remove(_tail.Key);
node.Key = key;
node.Value = value;
}
else
{
_currentCount++;
node = new LeastRecentlyUsedCacheNode {
Key = key, Value = value
};
}
_nodesByKey.Add(key, node);
}
}
else
{
//exists in cache so locak the node and update its' value
lock (node)
{
node.Value = value;
}
}
MakeMostRecentlyUsed(node);
if (_tail == null)
{
_tail = _head;
}
}
}
