/// <summary>
/// Caches some object <paramref name="Item"/>.
/// </summary>
/// <param name="HonestItemSizeInBytes">The size of <paramref name="Item"/> in bytes.</param>
/// <param name="Item">Object which should be cached.</param>
/// <returns>
/// A reference code for later access to the object <paramref name="Item"/>.
/// </returns>
public static ulong CacheItem(object Item, int HonestItemSizeInBytes)
{
RefCounter++;
Debug.Assert((!(Item is MultidimensionalArray)) || (((MultidimensionalArray)Item).Length * sizeof(double) == HonestItemSizeInBytes));
CacheBank cb = new CacheBank()
{
Item = Item,
MemSize = HonestItemSizeInBytes,
UseCount = 1,
Reference = RefCounter
};
while (CurrentSize + cb.MemSize > MaxMem)
{
if (!RemoveAtTail())
{
break;
}
}
int iBank = Insert(cb);
Debug.Assert(object.ReferenceEquals(Banks[iBank], cb));
Debug.Assert(cb.iBank == iBank);
ulong R = ((ulong)iBank);
R |= (((ulong)cb.Reference) << 32);
return(R);
}
/// <summary>
/// Returns true if the item stored under reference <paramref name="Reference"/> is still present in the cache, false otherwise.
/// In contrast to <see cref="GetItem"/>, this is cheaper and does not affect cache statistics.
/// </summary>
public static bool IsAlive(ulong Reference)
{
int iBank = (int)(Reference & 0x00000000FFFFFFFF);
int iref = (int)((Reference & 0xFFFFFFFF00000000) >> 32);
CacheBank cb = Banks[iBank];
return(cb != null && iref == cb.Reference);
}
static CacheBank Head; // dummy 'bank', marking the tail of the cache-ranking list (last object to discard)
static void Remove(int iBank)
{
CacheBank toRemove = Banks[iBank];
Debug.Assert(toRemove.iBank == iBank);
Banks[iBank] = null;
toRemove.prev.next = toRemove.next;
toRemove.next.prev = toRemove.prev;
CurrentSize = CurrentSize - toRemove.MemSize;
emptyBanks.Add(iBank);
m_NoOfUsedBanks--;
Debug.Assert(m_NoOfUsedBanks >= 0);
}
/// <summary>
/// Removes some cached item from the cache.
/// </summary>
public static void ForgetItem(ulong Reference)
{
int iBank = (int)(Reference & 0x00000000FFFFFFFF);
int iref = (int)((Reference & 0xFFFFFFFF00000000) >> 32);
CacheBank cb = Banks[iBank];
if ((cb != null && iref == cb.Reference))
{
// object is still in cache, so there is something to forget.
Remove(iBank);
}
}
static int Insert(CacheBank cb)
{
if (emptyBanks.Count > 0)
{
cb.iBank = emptyBanks[emptyBanks.Count - 1];
emptyBanks.RemoveAt(emptyBanks.Count - 1);
Debug.Assert(Banks[cb.iBank] == null);
Banks[cb.iBank] = cb;
}
else
{
cb.iBank = Banks.Count;
Banks.Add(cb);
}
m_NoOfUsedBanks++;
CurrentSize += cb.MemSize;// update the bank ranking:
switch (Strategy)
{
case CacheStrategy.DiscardLeastRecentyUsed:
// insert at head
cb.next = Head.next;
cb.prev = Head;
Head.next.prev = cb;
Head.next = cb;
break;
case CacheStrategy.DiscardLeastFrequentlyUsed:
// insert at tail
cb.next = Tail;
cb.prev = Tail.prev;
Tail.prev.next = cb;
Tail.prev = cb;
// bubble up until the sorting is ok.
BubbleUp(cb);
break;
default:
throw new NotImplementedException();
}
Debug.Assert(Banks[cb.iBank].iBank == cb.iBank);
return(cb.iBank);
}
static void ResetCache()
{
Tail = new CacheBank()
{
iBank = int.MinValue
};
Head = new CacheBank()
{
iBank = int.MinValue
};
Tail.prev = Head;
Head.next = Tail;
emptyBanks = new List <int>();
Banks = new List <CacheBank>();
CurrentSize = 0;
m_NoOfUsedBanks = 0;
}
private static void BubbleUp(CacheBank a)
{
while (
(!object.ReferenceEquals(a.prev, Head)) && // reached top of ranking
(a.UseCount >= a.prev.UseCount)) // >= prefers least-recently used in case of doubt
{
CacheBank p = a.prev;
CacheBank pp = p.prev;
CacheBank n = a.next;
pp.next = a;
a.next = p;
p.next = n;
a.prev = pp;
p.prev = a;
n.prev = p;
}
}
static CacheBank Access(int iBank)
{
CacheBank a = Banks[iBank];
if (a == null)
{
return(a);
}
a.UseCount++;
// update the bank ranking:
switch (Strategy)
{
case CacheStrategy.DiscardLeastRecentyUsed:
//
// remove 'a', where-ever it is...
a.prev.next = a.next;
a.next.prev = a.prev;
// ... and put it on top:
a.next = Head.next;
a.prev = Head;
Head.next.prev = a;
Head.next = a;
break;
case CacheStrategy.DiscardLeastFrequentlyUsed:
//
// bubble up until the sorting is ok.
BubbleUp(a);
break;
default:
throw new NotImplementedException();
}
return(a);
}
/// <summary>
/// Returns the item stored under reference <paramref name="Reference"/>
/// -- or --
/// null, if the object has been removed from the cache.
/// </summary>
public static object GetItem(ulong Reference)
{
int iBank = (int)(Reference & 0x00000000FFFFFFFF);
int iref = (int)((Reference & 0xFFFFFFFF00000000) >> 32);
CacheBank cb = Banks[iBank];
if (cb != null && iref == cb.Reference)
{
Access(iBank);
Hits++;
return(cb.Item);
}
else
{
Misses++;
return(null);
}
}
