461 lines
16 KiB
C#
461 lines
16 KiB
C#
//
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// Copyright (c) 2008-2011, Kenneth Bell
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//
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// Permission is hereby granted, free of charge, to any person obtaining a
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// copy of this software and associated documentation files (the "Software"),
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// to deal in the Software without restriction, including without limitation
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// the rights to use, copy, modify, merge, publish, distribute, sublicense,
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// and/or sell copies of the Software, and to permit persons to whom the
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// Software is furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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// DEALINGS IN THE SOFTWARE.
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//
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using System;
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using System.Collections.Generic;
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using System.IO;
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namespace DiscUtils.Streams
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{
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/// <summary>
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/// A stream implementing a block-oriented read cache.
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/// </summary>
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public sealed class BlockCacheStream : SparseStream
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{
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private bool _atEof;
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private readonly int _blocksInReadBuffer;
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private readonly BlockCache<Block> _cache;
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private readonly Ownership _ownWrapped;
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private long _position;
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private readonly byte[] _readBuffer;
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private readonly BlockCacheSettings _settings;
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private readonly BlockCacheStatistics _stats;
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private SparseStream _wrappedStream;
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/// <summary>
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/// Initializes a new instance of the BlockCacheStream class.
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/// </summary>
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/// <param name="toWrap">The stream to wrap.</param>
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/// <param name="ownership">Whether to assume ownership of <c>toWrap</c>.</param>
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public BlockCacheStream(SparseStream toWrap, Ownership ownership)
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: this(toWrap, ownership, new BlockCacheSettings()) {}
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/// <summary>
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/// Initializes a new instance of the BlockCacheStream class.
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/// </summary>
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/// <param name="toWrap">The stream to wrap.</param>
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/// <param name="ownership">Whether to assume ownership of <c>toWrap</c>.</param>
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/// <param name="settings">The cache settings.</param>
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public BlockCacheStream(SparseStream toWrap, Ownership ownership, BlockCacheSettings settings)
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{
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if (!toWrap.CanRead)
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{
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throw new ArgumentException("The wrapped stream does not support reading", nameof(toWrap));
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}
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if (!toWrap.CanSeek)
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{
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throw new ArgumentException("The wrapped stream does not support seeking", nameof(toWrap));
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}
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_wrappedStream = toWrap;
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_ownWrapped = ownership;
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_settings = new BlockCacheSettings(settings);
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if (_settings.OptimumReadSize % _settings.BlockSize != 0)
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{
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throw new ArgumentException("Invalid settings, OptimumReadSize must be a multiple of BlockSize",
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nameof(settings));
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}
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_readBuffer = new byte[_settings.OptimumReadSize];
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_blocksInReadBuffer = _settings.OptimumReadSize / _settings.BlockSize;
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int totalBlocks = (int)(_settings.ReadCacheSize / _settings.BlockSize);
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_cache = new BlockCache<Block>(_settings.BlockSize, totalBlocks);
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_stats = new BlockCacheStatistics();
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_stats.FreeReadBlocks = totalBlocks;
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}
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/// <summary>
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/// Gets an indication as to whether the stream can be read.
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/// </summary>
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public override bool CanRead
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{
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get { return true; }
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}
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/// <summary>
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/// Gets an indication as to whether the stream position can be changed.
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/// </summary>
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public override bool CanSeek
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{
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get { return true; }
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}
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/// <summary>
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/// Gets an indication as to whether the stream can be written to.
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/// </summary>
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public override bool CanWrite
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{
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get { return _wrappedStream.CanWrite; }
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}
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/// <summary>
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/// Gets the parts of the stream that are stored.
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/// </summary>
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/// <remarks>This may be an empty enumeration if all bytes are zero.</remarks>
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public override IEnumerable<StreamExtent> Extents
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{
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get
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{
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CheckDisposed();
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return _wrappedStream.Extents;
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}
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}
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/// <summary>
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/// Gets the length of the stream.
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/// </summary>
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public override long Length
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{
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get
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{
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CheckDisposed();
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return _wrappedStream.Length;
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}
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}
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/// <summary>
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/// Gets and sets the current stream position.
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/// </summary>
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public override long Position
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{
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get
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{
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CheckDisposed();
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return _position;
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}
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set
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{
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CheckDisposed();
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_position = value;
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}
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}
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/// <summary>
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/// Gets the performance statistics for this instance.
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/// </summary>
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public BlockCacheStatistics Statistics
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{
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get
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{
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_stats.FreeReadBlocks = _cache.FreeBlockCount;
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return _stats;
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}
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}
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/// <summary>
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/// Gets the parts of a stream that are stored, within a specified range.
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/// </summary>
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/// <param name="start">The offset of the first byte of interest.</param>
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/// <param name="count">The number of bytes of interest.</param>
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/// <returns>An enumeration of stream extents, indicating stored bytes.</returns>
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public override IEnumerable<StreamExtent> GetExtentsInRange(long start, long count)
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{
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CheckDisposed();
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return _wrappedStream.GetExtentsInRange(start, count);
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}
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/// <summary>
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/// Reads data from the stream.
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/// </summary>
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/// <param name="buffer">The buffer to fill.</param>
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/// <param name="offset">The buffer offset to start from.</param>
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/// <param name="count">The number of bytes to read.</param>
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/// <returns>The number of bytes read.</returns>
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public override int Read(byte[] buffer, int offset, int count)
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{
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CheckDisposed();
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if (_position >= Length)
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{
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if (_atEof)
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{
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throw new IOException("Attempt to read beyond end of stream");
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}
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_atEof = true;
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return 0;
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}
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_stats.TotalReadsIn++;
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if (count > _settings.LargeReadSize)
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{
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_stats.LargeReadsIn++;
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_stats.TotalReadsOut++;
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_wrappedStream.Position = _position;
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int numRead = _wrappedStream.Read(buffer, offset, count);
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_position = _wrappedStream.Position;
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if (_position >= Length)
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{
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_atEof = true;
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}
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return numRead;
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}
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int totalBytesRead = 0;
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bool servicedFromCache = false;
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bool servicedOutsideCache = false;
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int blockSize = _settings.BlockSize;
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long firstBlock = _position / blockSize;
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int offsetInNextBlock = (int)(_position % blockSize);
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long endBlock = MathUtilities.Ceil(Math.Min(_position + count, Length), blockSize);
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int numBlocks = (int)(endBlock - firstBlock);
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if (offsetInNextBlock != 0)
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{
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_stats.UnalignedReadsIn++;
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}
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int blocksRead = 0;
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while (blocksRead < numBlocks)
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{
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Block block;
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// Read from the cache as much as possible
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while (blocksRead < numBlocks && _cache.TryGetBlock(firstBlock + blocksRead, out block))
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{
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int bytesToRead = Math.Min(count - totalBytesRead, block.Available - offsetInNextBlock);
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Array.Copy(block.Data, offsetInNextBlock, buffer, offset + totalBytesRead, bytesToRead);
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offsetInNextBlock = 0;
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totalBytesRead += bytesToRead;
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_position += bytesToRead;
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blocksRead++;
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servicedFromCache = true;
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}
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// Now handle a sequence of (one or more) blocks that are not cached
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if (blocksRead < numBlocks && !_cache.ContainsBlock(firstBlock + blocksRead))
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{
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servicedOutsideCache = true;
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// Figure out how many blocks to read from the wrapped stream
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int blocksToRead = 0;
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while (blocksRead + blocksToRead < numBlocks
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&& blocksToRead < _blocksInReadBuffer
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&& !_cache.ContainsBlock(firstBlock + blocksRead + blocksToRead))
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{
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++blocksToRead;
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}
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// Allow for the end of the stream not being block-aligned
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long readPosition = (firstBlock + blocksRead) * blockSize;
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int bytesRead = (int)Math.Min(blocksToRead * (long)blockSize, Length - readPosition);
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// Do the read
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_stats.TotalReadsOut++;
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_wrappedStream.Position = readPosition;
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StreamUtilities.ReadExact(_wrappedStream, _readBuffer, 0, bytesRead);
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// Cache the read blocks
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for (int i = 0; i < blocksToRead; ++i)
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{
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int copyBytes = Math.Min(blockSize, bytesRead - i * blockSize);
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block = _cache.GetBlock(firstBlock + blocksRead + i);
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Array.Copy(_readBuffer, i * blockSize, block.Data, 0, copyBytes);
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block.Available = copyBytes;
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if (copyBytes < blockSize)
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{
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Array.Clear(_readBuffer, i * blockSize + copyBytes, blockSize - copyBytes);
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}
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}
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blocksRead += blocksToRead;
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// Propogate the data onto the caller
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int bytesToCopy = Math.Min(count - totalBytesRead, bytesRead - offsetInNextBlock);
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Array.Copy(_readBuffer, offsetInNextBlock, buffer, offset + totalBytesRead, bytesToCopy);
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totalBytesRead += bytesToCopy;
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_position += bytesToCopy;
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offsetInNextBlock = 0;
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}
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}
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if (_position >= Length && totalBytesRead == 0)
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{
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_atEof = true;
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}
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if (servicedFromCache)
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{
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_stats.ReadCacheHits++;
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}
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if (servicedOutsideCache)
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{
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_stats.ReadCacheMisses++;
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}
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return totalBytesRead;
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}
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/// <summary>
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/// Flushes the stream.
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/// </summary>
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public override void Flush()
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{
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CheckDisposed();
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_wrappedStream.Flush();
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}
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/// <summary>
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/// Moves the stream position.
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/// </summary>
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/// <param name="offset">The origin-relative location.</param>
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/// <param name="origin">The base location.</param>
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/// <returns>The new absolute stream position.</returns>
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public override long Seek(long offset, SeekOrigin origin)
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{
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CheckDisposed();
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long effectiveOffset = offset;
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if (origin == SeekOrigin.Current)
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{
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effectiveOffset += _position;
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}
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else if (origin == SeekOrigin.End)
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{
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effectiveOffset += Length;
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}
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_atEof = false;
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if (effectiveOffset < 0)
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{
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throw new IOException("Attempt to move before beginning of disk");
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}
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_position = effectiveOffset;
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return _position;
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}
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/// <summary>
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/// Sets the length of the stream.
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/// </summary>
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/// <param name="value">The new length.</param>
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public override void SetLength(long value)
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{
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CheckDisposed();
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_wrappedStream.SetLength(value);
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}
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/// <summary>
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/// Writes data to the stream at the current location.
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/// </summary>
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/// <param name="buffer">The data to write.</param>
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/// <param name="offset">The first byte to write from buffer.</param>
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/// <param name="count">The number of bytes to write.</param>
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public override void Write(byte[] buffer, int offset, int count)
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{
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CheckDisposed();
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_stats.TotalWritesIn++;
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int blockSize = _settings.BlockSize;
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long firstBlock = _position / blockSize;
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long endBlock = MathUtilities.Ceil(Math.Min(_position + count, Length), blockSize);
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int numBlocks = (int)(endBlock - firstBlock);
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try
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{
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_wrappedStream.Position = _position;
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_wrappedStream.Write(buffer, offset, count);
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}
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catch
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{
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InvalidateBlocks(firstBlock, numBlocks);
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throw;
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}
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int offsetInNextBlock = (int)(_position % blockSize);
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if (offsetInNextBlock != 0)
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{
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_stats.UnalignedWritesIn++;
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}
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// For each block touched, if it's cached, update it
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int bytesProcessed = 0;
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for (int i = 0; i < numBlocks; ++i)
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{
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int bufferPos = offset + bytesProcessed;
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int bytesThisBlock = Math.Min(count - bytesProcessed, blockSize - offsetInNextBlock);
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Block block;
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if (_cache.TryGetBlock(firstBlock + i, out block))
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{
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Array.Copy(buffer, bufferPos, block.Data, offsetInNextBlock, bytesThisBlock);
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block.Available = Math.Max(block.Available, offsetInNextBlock + bytesThisBlock);
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}
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offsetInNextBlock = 0;
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bytesProcessed += bytesThisBlock;
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}
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_position += count;
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}
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/// <summary>
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/// Disposes of this instance, freeing up associated resources.
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/// </summary>
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/// <param name="disposing"><c>true</c> if invoked from <c>Dispose</c>, else <c>false</c>.</param>
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protected override void Dispose(bool disposing)
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{
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if (disposing)
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{
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if (_wrappedStream != null && _ownWrapped == Ownership.Dispose)
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{
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_wrappedStream.Dispose();
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}
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_wrappedStream = null;
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}
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base.Dispose(disposing);
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}
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private void CheckDisposed()
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{
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if (_wrappedStream == null)
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{
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throw new ObjectDisposedException("BlockCacheStream");
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}
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}
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private void InvalidateBlocks(long firstBlock, int numBlocks)
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{
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for (long i = firstBlock; i < firstBlock + numBlocks; ++i)
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{
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_cache.ReleaseBlock(i);
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}
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}
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}
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} |