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/*
* Copyright (C) 2007-2010 Xagasoft, All rights reserved.
*
* This file is part of the libbu++ library and is released under the
* terms of the license contained in the file LICENSE.
*/
#ifndef BU_MYRIAD_H
#define BU_MYRIAD_H
#include <stdint.h>
#include "bu/bitstring.h"
#include "bu/exceptionbase.h"
#include "bu/array.h"
#include "bu/hash.h"
namespace Bu
{
class Stream;
class MyriadStream;
subExceptionDecl( MyriadException )
/**
* Numerically Indexed Data Streams. This is a working name so I can
* actually get some code written instead of agonizing over the name.
*
* This is a system for creating streams that contain other streams in
* a flexible block-allocated system.
*
* Header format is as follows:
*
* MMMMvBssssSSSS*
* M = Magic number (FFC399BD)
* v = version number
* B = Bits per int
* s = Blocksize in bytes
* S = Number of Streams
*
* The * represents the Stream headers, one per stream, as follows:
* IIIIssss$
* I = Id number of the stream
* s = size of stream in bytes
*
* The $ represents the Block headers, one per used block, as follows:
* IIII
* I = Index of the block
*
* The stream/block data is interleaved in the header, so all blocks stored
* with one stream are together. The block headers are in order, and the
* data in them is required to be "solid" you cannot fill partial blocks
* mid-way through a stream.
*
* The initial block starts with the nids header, and is both the zero block
* and the zero stream. For now, the minimum block size is the size needed
* to store the base header, the zero stream header, and the first two
* blocks of the zero stream, so 30 bytes. Since it's reccomended to use
* a size that will fit evenly into filesystem blocks, then a size of 32 is
* probably the smallest reccomended size because all powers of two equal
* to or greater than 32 are evenly divisible by 32.
*
* I have had a thought that if the block size were smaller than 42 bytes
* the header would consume the first N blocks where N * block size is
* enough space to house the initial header, the first stream header, and
* the first N block headers. This, of course, causes you to hit an
* infinite header if the block size is small enough.
*/
class Myriad
{
friend class MyriadStream;
public:
Myriad( Bu::Stream &sStore );
virtual ~Myriad();
/**
* Initialize this object based on the data already in the assosiated
* stream. This will be called automatically for you if you forget,
* but if you want to pre-initialize for some reason, just call this
* once before you actually start doing anything with your Myriad.
*/
void initialize();
/**
* Create a new Myriad system in the assosiated stream. This should be
* used carefully, it will destroy all data already within the stream.
* More options will probably be added soon.
*/
void initialize( int iBlockSize, int iPreAllocate=1 );
/**
* Create a new stream within the Myriad system. The ID of the new stream
* is returned.
*/
int createStream( int iPreAllocate=1 );
/**
* Delete a stream that's already within the Myriad.
*/
void deleteStream( int iId );
/**
* Return a new Stream object assosiated with the given stream ID.
*/
MyriadStream openStream( int iId );
int getBlockSize();
int getNumBlocks();
int getNumUsedBlocks();
int getBlockOverhead();
/**
* Syncronize the header data, etc. with the storage stream. It's not
* a bad idea to call this periodically.
*/
void sync();
private:
enum
{
blockUnused = 0xFFFFFFFFUL
};
typedef Bu::Array<int> BlockArray;
class Stream
{
public:
int iId;
int iSize;
BlockArray aBlocks;
};
typedef Bu::Array<Stream *> StreamArray;
class Block
{
public:
char *pData;
bool bChanged;
int iBlockIndex;
};
void updateHeader();
int findEmptyBlock();
/**
*@todo Change this to use a binary search, it's nicer.
*/
Stream *findStream( int iId );
Block *getBlock( int iBlock );
void releaseBlock( Block *pBlock );
void syncBlock( Block *pBlock );
private:
Bu::Stream &sStore;
int iBlockSize;
int iBlocks;
int iUsed;
Bu::BitString bsBlockUsed;
StreamArray aStreams;
typedef Bu::Hash<int, Block *> BlockHash;
BlockHash hActiveBlocks;
bool bHeaderChanged;
};
};
#endif
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