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/*
* Copyright (c) 2022 Vaughn Nugent
*
* Library: VNLib
* Package: VNLib.Data.Caching.ObjectCache
* File: BlobCache.cs
*
* BlobCache.cs is part of VNLib.Data.Caching.ObjectCache which is part of the larger
* VNLib collection of libraries and utilities.
*
* VNLib.Data.Caching.ObjectCache is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* VNLib.Data.Caching.ObjectCache is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see https://www.gnu.org/licenses/.
*/
using System;
using System.Collections.Generic;
using VNLib.Utils.Memory.Caching;
namespace VNLib.Data.Caching
{
/// <summary>
/// A general purpose binary data storage
/// </summary>
public class BlobCache : LRUCache<string, CacheEntry>
{
///<inheritdoc/>
public override bool IsReadOnly { get; }
///<inheritdoc/>
protected override int MaxCapacity { get; }
/// <summary>
/// Initializes a new <see cref="BlobCache"/> store
/// </summary>
/// <param name="maxCapacity">The maximum number of items to keep in memory</param>
/// <exception cref="ArgumentException"></exception>
public BlobCache(int maxCapacity)
:base(StringComparer.Ordinal)
{
if(maxCapacity < 1)
{
throw new ArgumentException("The maxium capacity of the store must be a positive integer larger than 0", nameof(maxCapacity));
}
MaxCapacity = maxCapacity;
//Update the lookup table size
LookupTable.EnsureCapacity(maxCapacity);
}
///<inheritdoc/>
protected override bool CacheMiss(string key, out CacheEntry value)
{
value = default;
return false;
}
///<inheritdoc/>
protected override void Evicted(ref KeyValuePair<string, CacheEntry> evicted)
{
//Dispose the cache item
evicted.Value.Dispose();
}
/// <summary>
/// If the <see cref="CacheEntry"/> is found in the store, changes the key
/// that referrences the blob.
/// </summary>
/// <param name="currentKey">The key that currently referrences the blob in the store</param>
/// <param name="newKey">The new key that will referrence the blob</param>
/// <param name="blob">The <see cref="CacheEntry"/> if its found in the store</param>
/// <returns>True if the record was found and the key was changes</returns>
public bool TryChangeKey(string currentKey, string newKey, out CacheEntry blob)
{
//Try to get the node at the current key
if (LookupTable.Remove(currentKey, out LinkedListNode<KeyValuePair<string, CacheEntry>> ? node))
{
//Remove the node from the ll
List.Remove(node);
//Get the stored blob
blob = node.ValueRef.Value;
//Update the
node.Value = new KeyValuePair<string, CacheEntry>(newKey, blob);
//Add to end of list
List.AddLast(node);
//Re-add to lookup table with new key
LookupTable.Add(newKey, node);
return true;
}
blob = default;
return false;
}
/// <summary>
/// Removes the <see cref="CacheEntry"/> from the store, and frees its resources
/// </summary>
/// <param name="key">The key that referrences the <see cref="CacheEntry"/> in the store</param>
/// <returns>A value indicating if the blob was removed</returns>
public override bool Remove(string key)
{
//Remove the item from the lookup table and if it exists, remove the node from the list
if (!LookupTable.Remove(key, out LinkedListNode<KeyValuePair<string, CacheEntry>>? node))
{
return false;
}
//always dispose blob
using (node.ValueRef.Value)
{
//Remove the node from the list
List.Remove(node);
}
return true;
}
/// <summary>
/// Removes all cache entires and disposes their held resources
/// </summary>
public override void Clear()
{
//Start from first node
LinkedListNode<KeyValuePair<string, CacheEntry>>? node = List.First;
//Classic ll node itteration
while(node != null)
{
//Dispose the cache entry
node.ValueRef.Value.Dispose();
//Move to next node
node = node.Next;
}
//empty all cache entires in the store
base.Clear();
}
}
}
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