public override bool Equals(Object obj)
{
if (this == obj)
{
return(true);
}
else if (!(obj is IndexCacheEntryKey))
{
return(false);
}
IndexCacheEntryKey other = (IndexCacheEntryKey)obj;
if (this.subFileParameter == null && other.subFileParameter != null)
{
return(false);
}
else if (this.subFileParameter != null && !this.subFileParameter.Equals(other.subFileParameter))
{
return(false);
}
else if (this.indexBlockNumber != other.indexBlockNumber)
{
return(false);
}
return(true);
}
/**
* Returns the index entry of a block in the given map file. If the required index entry is not cached, it will be
* read from the map file index and put in the cache.
*
* @param subFileParameter
* the parameters of the map file for which the index entry is needed.
* @param blockNumber
* the number of the block in the map file.
* @return the index entry.
* @throws IOException
* if an I/O error occurs during reading.
*/
public long getIndexEntry(SubFileParameter subFileParameter, long blockNumber)
{
// check if the block number is out of bounds
if (blockNumber >= subFileParameter.NumberOfBlocks)
{
throw new IOException("invalid block number: " + blockNumber);
}
// calculate the index block number
long indexBlockNumber = blockNumber / INDEX_ENTRIES_PER_BLOCK;
// create the cache entry key for this request
IndexCacheEntryKey indexCacheEntryKey = new IndexCacheEntryKey(subFileParameter, indexBlockNumber);
// check for cached index block
byte[] indexBlock;
if (!this.map.TryGetValue(indexCacheEntryKey, out indexBlock))
{
// cache miss, seek to the correct index block in the file and read it
long indexBlockPosition = subFileParameter.IndexStartAddress + indexBlockNumber * SIZE_OF_INDEX_BLOCK;
int remainingIndexSize = (int)(subFileParameter.IndexEndAddress - indexBlockPosition);
int indexBlockSize = Math.Min(SIZE_OF_INDEX_BLOCK, remainingIndexSize);
indexBlock = new byte[indexBlockSize];
this.Stream.Seek(indexBlockPosition, SeekOrigin.Begin);
if (this.Stream.Read(indexBlock, 0, indexBlockSize) != indexBlockSize)
{
throw new IOException("could not read index block with size: " + indexBlockSize);
}
// put the index block in the map
this.map.Add(indexCacheEntryKey, indexBlock);
}
// calculate the address of the index entry inside the index block
long indexEntryInBlock = blockNumber % INDEX_ENTRIES_PER_BLOCK;
int addressInIndexBlock = (int)(indexEntryInBlock * SubFileParameter.BytesPerIndexEntry);
// return the real index entry
return(Deserializer.GetLong(indexBlock, addressInIndexBlock, SubFileParameter.BytesPerIndexEntry));
}
