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/* ====================================================================
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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==================================================================== */
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namespace HH.WMS.Utils.NPOI.POIFS.FileSystem
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{
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using System;
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using HH.WMS.Utils.NPOI.POIFS.Storage;
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using HH.WMS.Utils.NPOI.POIFS.NIO;
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using HH.WMS.Utils.NPOI.Util;
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/// <summary>
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/// This abstract class describes a way to read, store, chain
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/// and free a series of blocks (be they Big or Small ones)
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/// </summary>
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public abstract class BlockStore
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{
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/// <summary>
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/// Returns the size of the blocks managed through the block store.
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/// </summary>
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/// <returns></returns>
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public abstract int GetBlockStoreBlockSize();
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/// <summary>
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/// Load the block at the given offset.
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/// </summary>
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/// <param name="offset"></param>
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/// <returns></returns>
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public abstract ByteBuffer GetBlockAt(int offset);
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/// <summary>
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/// Extends the file if required to hold blocks up to
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/// the specified offset, and return the block from there.
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/// </summary>
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/// <param name="offset"></param>
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/// <returns></returns>
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public abstract ByteBuffer CreateBlockIfNeeded(int offset);
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/// <summary>
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/// Returns the BATBlock that handles the specified offset,
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/// and the relative index within it
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/// </summary>
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/// <param name="offset"></param>
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/// <returns></returns>
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public abstract BATBlockAndIndex GetBATBlockAndIndex(int offset);
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/// <summary>
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/// Works out what block follows the specified one.
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/// </summary>
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/// <param name="offset"></param>
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/// <returns></returns>
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public abstract int GetNextBlock(int offset);
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/// <summary>
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/// Changes the record of what block follows the specified one.
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/// </summary>
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/// <param name="offset"></param>
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/// <param name="nextBlock"></param>
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public abstract void SetNextBlock(int offset, int nextBlock);
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/// <summary>
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/// Finds a free block, and returns its offset.
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/// This method will extend the file/stream if needed, and if doing
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/// so, allocate new FAT blocks to address the extra space.
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/// </summary>
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/// <returns></returns>
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public abstract int GetFreeBlock();
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/// <summary>
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/// Creates a Detector for loops in the chain
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/// </summary>
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/// <returns></returns>
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public abstract ChainLoopDetector GetChainLoopDetector();
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}
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/// <summary>
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/// Used to detect if a chain has a loop in it, so
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/// we can bail out with an error rather than
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/// spinning away for ever...
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/// </summary>
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public class ChainLoopDetector
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{
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private bool[] used_blocks;
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private BlockStore blockStore;
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public ChainLoopDetector(long rawSize, BlockStore blockStore)
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{
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this.blockStore = blockStore;
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int numBlocks = (int)Math.Ceiling(1.0 * (rawSize / blockStore.GetBlockStoreBlockSize()));
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used_blocks = new bool[numBlocks];
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}
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public void Claim(int offset)
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{
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if (offset >= used_blocks.Length)
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{
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// They're writing, and have had new blocks requested
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// for the write to proceed. That means they're into
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// blocks we've allocated for them, so are safe
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return;
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}
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// Claiming an existing block, ensure there's no loop
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if (used_blocks[offset])
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{
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throw new InvalidOperationException(
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"Potential loop detected - Block " + offset +
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" was already claimed but was just requested again"
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);
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}
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used_blocks[offset] = true;
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}
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}
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}
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