/// <summary>
/// A least recently used cache with a time to live.
/// </summary>
/// <param name="capacity">
/// The number of entries the cache will hold
/// </param>
/// <param name="hours">The number of hours in the TTL</param>
/// <param name="minutes">The number of minutes in the TTL</param>
/// <param name="seconds">The number of seconds in the TTL</param>
/// <param name="refreshEntries">
/// Whether the TTL should be refreshed upon retrieval
/// </param>
public LRUCache(
int capacity,
int hours = 0,
int minutes = 0,
int seconds = 0,
bool refreshEntries = true)
{
this._capacity = capacity;
this._entries = new Dictionary <K, CacheNode>(this._capacity);
this._head = null;
this._tail = null;
this._count = 0;
this._ttl = new TimeSpan(hours, minutes, seconds);
this._refreshEntries = refreshEntries;
if (this._ttl > TimeSpan.Zero)
{
this._timer = new Timer(
Purge,
null,
(int)this._ttl.TotalMilliseconds,
5000); // 5 seconds
}
}
private void RemoveFromLL(CacheNode entry)
{
var next = entry.Next;
var prev = entry.Prev;
if (null != next)
{
next.Prev = entry.Prev;
}
if (null != prev)
{
prev.Next = entry.Next;
}
if (this._head == entry)
{
this._head = next;
}
if (this._tail == entry)
{
this._tail = prev;
}
}
private void RemoveLeastRecentlyUsed()
{
cachedItems.Remove(tail.Key);
tail.Previous.Next = null;
tail = tail.Previous;
}
/// <summary>
/// Sets the item being stored to the supplied value.
/// </summary>
/// <param name="key">The cache key.</param>
/// <param name="value">The value to set in the cache.</param>
/// <returns>True if the set was successful. False otherwise.</returns>
public bool TryAdd(K key, V value)
{
CacheNode entry;
if (!this._entries.TryGetValue(key, out entry))
{
// Add the entry
lock (this)
{
if (!this._entries.TryGetValue(key, out entry))
{
if (this.IsFull)
{
// Re-use the CacheNode entry
entry = this._tail;
_entries.Remove(this._tail.Key);
// Reset with new values
entry.Key = key;
entry.Value = value;
entry.LastAccessed = DateTime.UtcNow;
// Next and Prev don't need to be reset.
// Move to front will do the right thing.
}
else
{
this._count++;
entry = new CacheNode()
{
Key = key,
Value = value,
LastAccessed = DateTime.UtcNow
};
}
_entries.Add(key, entry);
}
}
}
else
{
// If V is a nonprimitive Value type (struct) then sets are
// not atomic, therefore we need to lock on the entry.
lock (entry)
{
entry.Value = value;
}
}
MoveToHead(entry);
// We don't need to lock here because two threads at this point
// can both happily perform this check and set, since they are
// both atomic.
if (null == this._tail)
{
this._tail = this._head;
}
return(true);
}
