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/*
* Copyright (c) 2023 Vaughn Nugent
*
* Library: VNLib
* Package: VNLib.Data.Caching.ObjectCache
* File: BlobCacheTable.cs
*
* BlobCacheTable.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.Linq;
using System.Collections;
using System.Collections.Generic;
using VNLib.Utils;
using VNLib.Utils.Memory;
namespace VNLib.Data.Caching.ObjectCache
{
/// <summary>
/// A concrete implementation of a <see cref="IBlobCacheTable"/>
/// </summary>
public sealed class BlobCacheTable : VnDisposeable, IBlobCacheTable
{
private readonly uint _tableSize;
private readonly IBlobCacheBucket[] _buckets;
/// <summary>
/// Initializes a new <see cref="BlobCacheTable"/>
/// </summary>
/// <param name="bucketSize">The number of elements in each bucket</param>
/// <param name="tableSize">The number of buckets within the table</param>
/// <param name="heap">The heap used to allocate cache entry buffers from</param>
/// <exception cref="ArgumentNullException"></exception>
/// <exception cref="ArgumentException"></exception>
public BlobCacheTable(uint tableSize, uint bucketSize, IUnmangedHeap heap)
{
_ = heap ?? throw new ArgumentNullException(nameof(heap));
if(tableSize == 0)
{
throw new ArgumentException("Cache table must have atleast 1 bucket");
}
//Init bucket table
_tableSize = tableSize;
_buckets = new IBlobCacheBucket[tableSize];
//Init buckets
InitBuckets(tableSize, bucketSize, _buckets, heap);
}
private static void InitBuckets(uint size, uint bucketSize, IBlobCacheBucket[] table, IUnmangedHeap heap)
{
for(int i = 0; i < size; i++)
{
table[i] = new BlobCacheBucket((int)bucketSize, heap);
}
}
/*
* A very simple algorithm that captures unique values
* from an object id and builds an unsigned 32bit integer
* used to determine the bucked index within the table.
*
* This method will alawys result in the same index for
* for a given object-id
*/
private uint FastGetBucketIndexFromId(ReadOnlySpan<char> objectId)
{
if (objectId.Length < 4)
{
throw new ArgumentException("Object id must be larger than 3 characters");
}
Span<byte> buffer = stackalloc byte[4];
//cast the characters
buffer[0] = (byte)objectId[0];
buffer[1] = (byte)objectId[objectId.Length / 2];
buffer[2] = (byte)objectId[1];
buffer[3] = (byte)objectId[^1];
//Read the buffer back to a uint and mod by the table size to get the bucket index
return BitConverter.ToUInt32(buffer) % _tableSize;
}
///<inheritdoc/>
///<exception cref="ObjectDisposedException"></exception>
public IBlobCacheBucket GetBucket(ReadOnlySpan<char> objectId)
{
Check();
//If tablesize is 1, skip lookup, otherwise perform bucket index lookup
uint index = _tableSize == 1 ? 0 : FastGetBucketIndexFromId(objectId);
return _buckets[index];
}
///<inheritdoc/>
protected sealed override void Free()
{
//Dispose buckets
Array.ForEach(_buckets, static b => b.Dispose());
}
///<inheritdoc/>
public IEnumerator<IBlobCacheBucket> GetEnumerator()
{
Check();
return _buckets.AsEnumerable().GetEnumerator();
}
///<inheritdoc/>
IEnumerator IEnumerable.GetEnumerator()
{
Check();
return _buckets.AsEnumerable().GetEnumerator();
}
}
}
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