using System; using System.Collections.Generic; using libsecondlife; namespace Opensim.Framework { // The delegate we will use for performing fetch from backing store // public delegate Object FetchDelegate(LLUUID index); public delegate bool ExpireDelegate(LLUUID index); // Strategy // // Conservative = Minimize memory. Expire items quickly. // Balanced = Expire items with few hits quickly. // Aggressive = Keep cache full. Expire only when over 90% and adding // public enum CacheStrategy { Conservative = 0, Balanced = 1, Aggressive = 2 } // Select classes to store data on different media // public enum CacheMedium { Memory = 0, File = 1 } public enum CacheFlags { CacheMissing = 1, AllowUpdate = 2 } // The base class of all cache objects. Implements comparison and sorting // by the LLUUID member. // // This is not abstract because we need to instantiate it briefly as a // method parameter // public class CacheItemBase : IEquatable<CacheItemBase>, IComparable<CacheItemBase> { public LLUUID uuid; public DateTime entered; public DateTime lastUsed; public DateTime expires = new DateTime(0); public int hits = 0; public virtual Object Retrieve() { return null; } public virtual void Store(Object data) { } public CacheItemBase(LLUUID index) { uuid = index; entered = DateTime.Now; lastUsed = entered; } public CacheItemBase(LLUUID index, DateTime ttl) { uuid = index; entered = DateTime.Now; lastUsed = entered; expires = ttl; } public virtual bool Equals(CacheItemBase item) { return uuid == item.uuid; } public virtual int CompareTo(CacheItemBase item) { return uuid.CompareTo(item.uuid); } public virtual bool IsLocked() { return false; } } // Simple in-memory storage. Boxes the object and stores it in a variable // public class MemoryCacheItem : CacheItemBase { private Object m_Data; public MemoryCacheItem(LLUUID index) : base(index) { } public MemoryCacheItem(LLUUID index, DateTime ttl) : base(index, ttl) { } public MemoryCacheItem(LLUUID index, Object data) : base(index) { Store(data); } public MemoryCacheItem(LLUUID index, DateTime ttl, Object data) : base(index, ttl) { Store(data); } public override Object Retrieve() { return m_Data; } public override void Store(Object data) { m_Data = data; } } // Simple persistent file storage // public class FileCacheItem : CacheItemBase { public FileCacheItem(LLUUID index) : base(index) { } public FileCacheItem(LLUUID index, DateTime ttl) : base(index, ttl) { } public FileCacheItem(LLUUID index, Object data) : base(index) { Store(data); } public FileCacheItem(LLUUID index, DateTime ttl, Object data) : base(index, ttl) { Store(data); } public override Object Retrieve() { //TODO: Add file access code return null; } public override void Store(Object data) { //TODO: Add file access code } } // The main cache class. This is the class you instantiate to create // a cache // public class Cache { private List<CacheItemBase> m_Index = new List<CacheItemBase>(); private Dictionary<LLUUID, CacheItemBase> m_Lookup = new Dictionary<LLUUID, CacheItemBase>(); private CacheStrategy m_Strategy; private CacheMedium m_Medium; private CacheFlags m_Flags = 0; private int m_Size = 1024; private TimeSpan m_DefaultTTL = new TimeSpan(0); public ExpireDelegate OnExpire; // Comparison interfaces // private class SortLRU : IComparer<CacheItemBase> { public int Compare(CacheItemBase a, CacheItemBase b) { if (a == null && b == null) return 0; if (a == null) return -1; if (b == null) return 1; return(a.lastUsed.CompareTo(b.lastUsed)); } } // Convenience constructors // public Cache() { m_Strategy = CacheStrategy.Balanced; m_Medium = CacheMedium.Memory; m_Flags = 0; } public Cache(CacheMedium medium) : this(medium, CacheStrategy.Balanced) { } public Cache(CacheMedium medium, CacheFlags flags) : this(medium, CacheStrategy.Balanced, flags) { } public Cache(CacheMedium medium, CacheStrategy strategy) : this(medium, strategy, 0) { } public Cache(CacheStrategy strategy, CacheFlags flags) : this(CacheMedium.Memory, strategy, flags) { } public Cache(CacheFlags flags) : this(CacheMedium.Memory, CacheStrategy.Balanced, flags) { } public Cache(CacheMedium medium, CacheStrategy strategy, CacheFlags flags) { m_Strategy = strategy; m_Medium = medium; m_Flags = flags; } // Count of the items currently in cache // public int Count { get { lock (m_Index) { return m_Index.Count; } } } // Maximum number of items this cache will hold // public int Size { get { return m_Size; } set { SetSize(value); } } private void SetSize(int newSize) { lock (m_Index) { if (Count <= Size) return; m_Index.Sort(new SortLRU()); m_Index.Reverse(); m_Index.RemoveRange(newSize, Count - newSize); m_Size = newSize; m_Lookup.Clear(); foreach (CacheItemBase item in m_Index) m_Lookup[item.uuid] = item; } } public TimeSpan DefaultTTL { get { return m_DefaultTTL; } set { m_DefaultTTL = value; } } // Get an item from cache. Return the raw item, not it's data // protected virtual CacheItemBase GetItem(LLUUID index) { CacheItemBase item = null; lock (m_Index) { if (m_Lookup.ContainsKey(index)) item = m_Lookup[index]; } if (item == null) { Expire(true); return null; } item.hits++; item.lastUsed = DateTime.Now; Expire(true); return item; } // Get an item from cache. Do not try to fetch from source if not // present. Just return null // public virtual Object Get(LLUUID index) { CacheItemBase item = GetItem(index); if (item == null) return null; return item.Retrieve(); } // Fetch an object from backing store if not cached, serve from // cache if it is. // public virtual Object Get(LLUUID index, FetchDelegate fetch) { Object item = Get(index); if (item != null) return item; Object data = fetch(index); if (data == null) { if ((m_Flags & CacheFlags.CacheMissing) != 0) { lock (m_Index) { CacheItemBase missing = new CacheItemBase(index); if (!m_Index.Contains(missing)) { m_Index.Add(missing); m_Lookup[index] = missing; } } } return null; } Store(index, data); return data; } // Find an object in cache by delegate. // public Object Find(Predicate<Opensim.Framework.CacheItemBase> d) { CacheItemBase item = m_Index.Find(d); if (item == null) return null; return item.Retrieve(); } public virtual void Store(LLUUID index, Object data) { Type container; switch (m_Medium) { case CacheMedium.Memory: container = typeof(MemoryCacheItem); break; case CacheMedium.File: return; default: return; } Store(index, data, container); } public virtual void Store(LLUUID index, Object data, Type container) { Store(index, data, container, new Object[] { index }); } public virtual void Store(LLUUID index, Object data, Type container, Object[] parameters) { Expire(false); CacheItemBase item; lock (m_Index) { if (m_Index.Contains(new CacheItemBase(index))) { if ((m_Flags & CacheFlags.AllowUpdate) != 0) { item = GetItem(index); item.hits++; item.lastUsed = DateTime.Now; if (m_DefaultTTL.Ticks != 0) item.expires = DateTime.Now + m_DefaultTTL; item.Store(data); } return; } item = (CacheItemBase)Activator.CreateInstance(container, parameters); if (m_DefaultTTL.Ticks != 0) item.expires = DateTime.Now + m_DefaultTTL; m_Index.Add(item); m_Lookup[index] = item; } item.Store(data); } protected virtual void Expire(bool getting) { if (getting && (m_Strategy == CacheStrategy.Aggressive)) return; if (m_DefaultTTL.Ticks != 0) { DateTime now= System.DateTime.Now; foreach (CacheItemBase item in new List<CacheItemBase>(m_Index)) { if (item.expires.Ticks == 0 || item.expires <= now) { m_Index.Remove(item); m_Lookup.Remove(item.uuid); } } } switch (m_Strategy) { case CacheStrategy.Aggressive: if (Count < Size) return; lock (m_Index) { m_Index.Sort(new SortLRU()); m_Index.Reverse(); int target = (int)((float)Size * 0.9); if (target == Count) // Cover ridiculous cache sizes return; ExpireDelegate doExpire = OnExpire; if (doExpire != null) { List<CacheItemBase> candidates = m_Index.GetRange(target, Count - target); foreach (CacheItemBase i in candidates) { if (doExpire(i.uuid)) { m_Index.Remove(i); m_Lookup.Remove(i.uuid); } } } else { m_Index.RemoveRange(target, Count - target); m_Lookup.Clear(); foreach (CacheItemBase item in m_Index) m_Lookup[item.uuid] = item; } } break; default: break; } } public void Invalidate(LLUUID uuid) { if (!m_Lookup.ContainsKey(uuid)) return; CacheItemBase item = m_Lookup[uuid]; m_Lookup.Remove(uuid); m_Index.Remove(item); } } }