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Add DataBlockCache template class. It parses but I don't know if it compiles yet.

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Updates #951, #965, #990.

Originally committed to SVN as r3412.
This commit is contained in:
Niels Martin Hansen 2009-08-15 21:48:58 +00:00
parent 324094960b
commit 76d94ec94c
1 changed files with 297 additions and 0 deletions
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aegisub/src/block_cache.h Normal file
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// Copyright (c) 2009, Niels Martin Hansen
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// * Redistributions of source code must retain the above copyright notice,
// this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright notice,
// this list of conditions and the following disclaimer in the documentation
// and/or other materials provided with the distribution.
// * Neither the name of the Aegisub Group nor the names of its contributors
// may be used to endorse or promote products derived from this software
// without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
//
// Aegisub Project http://www.aegisub.org/
//
// $Id$
/// @file block_cache.h
/// @ingroup utility
/// @brief Template class for creating caches for blocks of data
// Include guard
#ifndef BLOCK_CACHE_H
#define BLOCK_CACHE_H
#include <vector>
/// @class BasicDataBlockFactory
/// @brief Simple factory for allocating blocks for DataBlockCache
/// @tparam BlockT Type of blocks to produce
///
/// This is the default block factory class used by DataBlockCache if another isn't specified.
/// It allocates blocks on the heap using operator new and the default constructor, and does
/// nothing special to initialise the blocks.
///
/// Custom block factories could use a large internally pre-allocated buffer to create the
/// requested blocks in to avoid the default allocator.
template <class BlockT>
struct BasicDataBlockFactory {
/// @brief Allocates a block and returns it
/// @param i Index of the block to allocate
/// @return A pointer to the allocated block
///
/// This default implementation does not use the i parameter. Custom implementations
/// of block factories should use i to determine what data to fill into the block.
BlockT *ProduceBlock(size_t i)
{
(void)i;
return new BlockT;
}
/// @brief De-allocate a block
/// @param block Pointer to the block to de-allocate
///
/// It is guaranteed that block was returned by ProduceBlock.
void DisposeBlock(BlockT *block)
{
delete block;
}
/// @brief Retrieve the amount of memory consumed by a single block
/// @return Number of bytes consumed by a block
///
/// All blocks must consume the same amount of memory. The size of a block
/// is used to manage and limit the size of the cache.
size_t GetBlockSize() const
{
return sizeof(BlockT);
}
};
/// @class DataBlockCache
/// @brief Cache for blocks of data in a stream or similar
/// @tparam BlockT Type of blocks to store
/// @tparam MacroblockExponent Controls the number of blocks per macroblock, for tuning memory usage
/// @tparam BlockFactoryT Type of block factory, see BasicDataBlockFactory class for detail on these
template <
class BlockT,
int MacroblockExponent = 6,
class BlockFactoryT = BasicDataBlockFactory<BlockT>
>
class DataBlockCache {
/// Type of an array of blocks
typedef std::vector<BlockT*> BlockArray;
struct MacroBlock {
int access_count;
BlockArray blocks;
};
/// Type of an array of macro blocks
typedef std::vector<MacroBlock> MacroBlockArray;
/// The data in the cache
MacroBlockArray data;
/// Number of blocks per macroblock
size_t macroblock_size;
/// Bitmask to extract the inside-macroblock index for a block by bitwise and
size_t macroblock_index_mask;
/// Factory object for blocks
BlockFactoryT factory;
/// @brief Dispose of all blocks in a macroblock and mark it empty
/// @param mb_index Index of macroblock to clear
void KillMacroBlock(size_t mb_index)
{
MacroBlock &mb = data[mb_index];
mb.access_count = 0;
for (size_t bi = 0; bi < blocks.size(); ++bi)
{
BlockT *b = mb.blocks[bi];
if (!b)
factory.DisposeBlock(b);
}
mb.blocks.clear();
}
public:
/// @brief Constructor
/// @param block_count Total number of blocks the cache will manage
/// @param factory Factory object to use for producing blocks
///
/// Note that the block_count is the maximum block index the cache will ever see,
/// it is an error to request a block number greater than block_count.
///
/// The factory object passed must respond well to copying.
DataBlockCache(size_t block_count, BlockFactoryT factory = BlockFactoryT())
: factory(factory)
{
macroblock_size = 1 << MacroblockExponent;
macroblock_index_mask = ~(((~0) >> MacroblockExponent) << MacroblockExponent);
data.resize( (block_count + macroblock_size - 1) >> MacroblockExponent );
}
/// @brief Destructor
///
/// Disposes of all cached blocks
~DataBlockCache()
{
// Clear all blocks by aging to zero bytes
Age(0);
}
/// @brief Clean up the cache
/// @param max_size Target maximum size of the cache in bytes
///
/// Passing a max_size of 0 (zero) causes the cache to be completely flushed
/// in a fast manner.
///
/// The max_size is not a hard limit, the cache size might somewhat exceed the max
/// after the aging operation, though it shouldn't be by much.
void Age(size_t max_size)
{
// Quick way out: get rid of everything
if (max_size == 0)
{
for (size_t mbi = 0; mbi < data.size(); ++mbi)
{
KillMacroBlock(mbi);
}
return;
}
// Get a list of macro blocks sorted by access count
struct AccessData {
MacroBlockArray::iterator mb;
AccessData(MacroBlockArray::iterator i) : mb(i) { }
// Sort in decreasing order: most accesses first
bool operator < (const AccessData &other) { return mb->access_count > other.mb->access_count; }
};
std::vector<AccessData> access_data;
access_data.reserve(data.size());
for (MacroBlockArray::iterator mb = data.begin(); mb != data.end(); ++mb)
access_data.push_back(AccessData(mb));
access_data.sort();
// Sum up data size until we hit the max
size_t cur_size = 0;
size_t block_size = factory.GetBlockSize();
size_t mbi = 0;
for (; mbi < data.size(); ++mbi)
{
BlockArray &ba = data[mbi].blocks;
for (size_t i = 0; i < ba.size(); ++i)
{
if (ba[i] != 0)
cur_size += block_size;
}
// Cut access count in half for live blocks, so parts that don't get accessed
// a lot will eventually be killed off.
data[mbi].access_count /= 2;
if (cur_size >= max_size)
{
++mbi;
break;
}
}
// Hit max, clear all remaining blocks
for (; mbi < data.size(); ++mbi)
{
KillMacroBlock(mbi);
}
}
/// @brief Obtain a data block from the cache
/// @param i Index of the block to retrieve
/// @param[out] created On return, tells whether the returned block was created during the operation
/// @return A pointer to the block in cache
///
/// It is legal to pass 0 (null) for created, in this case nothing is returned in it.
BlockT *Get(size_t i, bool *created = 0)
{
size_t mbi = i >> MacroblockExponent;
assert(mbi < data.size());
MacroBlock &mb = data[mbi];
mb.access_count += 1;
if (mb.blocks.size() == 0)
{
mb.blocks.resize(macroblock_size);
}
size_t block_index = i & macroblock_index_mask;
assert(block_index < mb.blocks.size());
BlockT *b = mb.blocks[block_index];
if (!b)
{
b = factory.ProduceBlock(i);
assert(b != 0);
mb.blocks[block_index] = b;
if (created) *created = true;
}
else
if (created) *created = false;
return b;
}
/// @brief Speculatively add blocks not present to the cache
/// @param forward Assume forwards linear access is plausible
/// @param backward Assume backwards linear access is plausible
/// @return Number of blocks added to the cache
///
/// Assuming forwards and/or backwards linear access causes the macroblock access data to be
/// used for speculating in macroblocks that may be accessed soon, and also allocate block
/// in macroblocks that may otherwise not have been accessed recently.
///
/// @todo Implement this.
size_t Speculate(bool forward, bool backward)
{
(void)forward;
(void)backward;
return 0;
}
};
// Include guard
#endif