private void MoveToHead(LRUCacheNode node)
{
_head.prev = node;
node.next = _head;
node.prev = null;
_head = node;
}
public bool TryGetValue(K key, out V val)
{
_counters.CacheReadPerSec.Increment();
LRUCacheNode node = null;
lock (_syncRoot) {
if (_data.TryGetValue(key, out node))
{
_order.Remove(node.TimeKey);
node.TimeKey = Stopwatch.GetTimestamp();
AddOrder(node.TimeKey, key);
}
}
if (node == null)
{
_counters.CacheHitRatio.IncreaseFraction(false);
val = default(V);
return(false);
}
else
{
_counters.CacheHitRatio.IncreaseFraction(true);
val = node.Value;
return(true);
}
}
private void Evict()
{
_keyToNodeDictionary.Remove(_tail.key);
_tail = _tail?.prev;
if (_tail?.next != null)
{
_tail.next = null;
}
}
/// <summary>
/// Set or insert the value if the key is not already present. When the cache reached its capacity, it should invalidate the least recently used item before inserting a new item.
/// </summary>
/// <param name="key"></param>
/// <param name="value"></param>
public void Insert(string key, int value)
{
LRUCacheNode newEntry;
if (_keyToNodeDictionary.ContainsKey(key))
{
_keyToNodeDictionary[key].val = value;
newEntry = _keyToNodeDictionary[key];
// Update MRU and LRU in case they point to this node
if (newEntry == _tail)
{
_tail = _tail.prev;
}
else if (newEntry == _head)
{
_head = _head.next;
}
// Detach from DLL
newEntry.Detach();
}
else
{
newEntry = new LRUCacheNode(key, value);
// Eviction based on LRU
if (_currentSize == _maxSize)
{
Evict();
}
else
{
_currentSize++; // Only increment if it is not contained and currentSize < maxsize
}
_keyToNodeDictionary.Add(newEntry.key, newEntry);
}
// Update MRU
var prevHead = _head;
_head = newEntry;
_head.next = prevHead;
if (prevHead != null)
{
prevHead.prev = _head;
}
if (_tail == null)
{
_tail = newEntry;
}
}
public void Put(int key, int value)
{
if (_map.ContainsKey(key))
{
var node = _map[key];
node.val = value;
if (_head == node)
{
return;
}
else if (node == _tail)
{
RemoveTail();
}
else
{
RemoveNode(node);
}
MoveToHead(node);
}
else
{
var node = new LRUCacheNode(key, value);
_map.Add(key, node);
if (_count == _capacity) // evicts
{
MoveToHead(node);
_map.Remove(_tail.key);
RemoveTail();
}
else
{
if (_head == null) // count 0
{
_head = _tail = node;
}
else if (_head == _tail) // count 1
{
_tail.prev = node;
node.next = _tail;
_head = node;
}
else
{
MoveToHead(node);
}
_count++;
}
}
}
/// <summary>
/// Helper function to detach a node from the DLL List
/// </summary>
public void Detach()
{
if (prev != null)
{
prev.next = next;
}
if (next != null)
{
next.prev = prev;
}
prev = null;
next = null;
}
private void RemoveNode(LRUCacheNode node)
{
var prev = node.prev;
var next = node.next;
if (prev != null)
{
prev.next = next;
}
if (next != null)
{
next.prev = prev;
}
}
private void RemoveTail()
{
_tail = _tail.prev;
_tail.next = null;
}
