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