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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.IO;
using System.Linq;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using VNLib.Utils.IO;
using VNLib.Utils.Logging;
using VNLib.Utils.Memory;
using VNLib.Utils.Memory.Caching;
namespace VNLib.Data.Caching
{
/// <summary>
/// A general purpose binary data storage
/// </summary>
public class BlobCache : LRUCache<string, MemoryHandle<byte>>
{
readonly IUnmangedHeap Heap;
readonly DirectoryInfo SwapDir;
readonly ILogProvider Log;
///<inheritdoc/>
public override bool IsReadOnly { get; }
///<inheritdoc/>
protected override int MaxCapacity { get; }
/// <summary>
/// Initializes a new <see cref="BlobCache"/> store
/// </summary>
/// <param name="swapDir">The <see cref="IsolatedStorageDirectory"/> to swap blob data to when cache</param>
/// <param name="maxCapacity">The maximum number of items to keep in memory</param>
/// <param name="log">A <see cref="ILogProvider"/> to write log data to</param>
/// <param name="heap">A <see cref="IUnmangedHeap"/> to allocate buffers and store <see cref="BlobItem"/> data in memory</param>
public BlobCache(DirectoryInfo swapDir, int maxCapacity, ILogProvider log, IUnmangedHeap heap)
:base(StringComparer.Ordinal)
{
IsReadOnly = false;
MaxCapacity = maxCapacity;
SwapDir = swapDir;
//Update the lookup table size
LookupTable.EnsureCapacity(maxCapacity);
//Set default heap if not specified
Heap = heap;
Log = log;
}
///<inheritdoc/>
protected override bool CacheMiss(string key, [NotNullWhen(true)] out MemoryHandle<byte>? value)
{
value = null;
return false;
}
///<inheritdoc/>
protected override void Evicted(KeyValuePair<string, MemoryHandle<byte>> evicted)
{
//Dispose the blob
evicted.Value.Dispose();
}
/// <summary>
/// If the <see cref="BlobItem"/> 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="BlobItem"/> 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, [NotNullWhen(true)] out MemoryHandle<byte>? blob)
{
if (LookupTable.Remove(currentKey, out LinkedListNode<KeyValuePair<string, MemoryHandle<byte>>>? node))
{
//Remove the node from the ll
List.Remove(node);
//Update the node kvp
blob = node.Value.Value;
node.Value = new KeyValuePair<string, MemoryHandle<byte>>(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 = null;
return false;
}
/// <summary>
/// Removes the <see cref="BlobItem"/> from the store without disposing the blobl
/// </summary>
/// <param name="key">The key that referrences the <see cref="BlobItem"/> 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, MemoryHandle<byte>>>? node))
{
//Remove the new from the list
List.Remove(node);
//dispose the buffer
node.Value.Value.Dispose();
return true;
}
return false;
}
/// <summary>
/// Removes and disposes all blobl elements in cache (or in the backing store)
/// </summary>
public override void Clear()
{
foreach (MemoryHandle<byte> blob in List.Select(kp => kp.Value))
{
blob.Dispose();
}
base.Clear();
}
}
}
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