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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
namespace MS.Internal.Printing
{
internal class MostFrequentlyUsedCache<K, V>
{
public MostFrequentlyUsedCache(int maxEntries)
{
if(maxEntries <= 0)
{
throw new ArgumentOutOfRangeException("maxEntries", maxEntries, string.Empty);
}
this._dictionary = new Dictionary<K, Entry>(maxEntries);
this._maxEntries = maxEntries;
}
public void CacheValue(K key, V value)
{
Entry entry;
if(!this._dictionary.TryGetValue(key, out entry))
{
entry = new Entry(value);
// Trim the dictionary to make sure it does not exceed
// maxEntries entries
while(this._dictionary.Count >= this._maxEntries)
{
RemoveLeastFrequentlyUsedEntry();
}
Debug.Assert(this._dictionary.Count <= this._maxEntries);
this._dictionary.Add(key, entry);
}
else
{
entry.Value = value;
entry.UseCount = 0;
}
}
public bool TryGetValue(K key, out V value)
{
Entry entry;
if(this._dictionary.TryGetValue(key, out entry))
{
value = entry.Value;
entry.UseCount++;
return true;
}
value = default(V);
return false;
}
private void RemoveLeastFrequentlyUsedEntry()
{
int minUseCount = int.MaxValue;
K minUseCountKey = default(K);
bool keyFound = false;
foreach(KeyValuePair<K, Entry> pair in this._dictionary)
{
if(pair.Value.UseCount < minUseCount)
{
minUseCount = pair.Value.UseCount;
minUseCountKey = pair.Key;
keyFound = true;
}
}
if(keyFound)
{
this._dictionary.Remove(minUseCountKey);
}
}
class Entry {
public Entry(V value)
{
Value = value;
}
public V Value;
public int UseCount;
}
private readonly IDictionary<K, Entry> _dictionary;
private readonly int _maxEntries;
}
} |