mirror of
https://github.com/ksherlock/profuse.git
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120 lines
2.3 KiB
C++
120 lines
2.3 KiB
C++
#include "BlockCache.h"
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#include "BlockDevice.h"
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#include "auto.h"
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#include <algorithm>
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/*
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* Note -- everything is assumed to be single-threaded.
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*
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*/
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using namespace ProFUSE;
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typedef std::vector<BlockDescriptor>::iterator BDIter;
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const unsigned CacheSize = 16;
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BlockCache::BlockCache(BlockDevice *device)
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{
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_device = device;
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_ts = 0;
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_blocks.reserve(CacheSize);
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}
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BlockCache::~BlockCache()
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{
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for (BDIter iter = _blocks.begin(); iter != _blocks.end(); ++iter)
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{
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if (iter->data) delete[] iter->data;
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}
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}
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void *BlockCache::acquire(unsigned block)
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{
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unsigned mints = -1;
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unsigned freeCount = 0;
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BDIter oldest;
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++_ts;
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/*
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* keep a pointer to the oldest free entry (according to ts).
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* and re-use if >= 16 entries.
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*/
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for (BDIter iter = _blocks.begin(); iter != _blocks.end(); ++iter)
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{
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if (iter->block == block)
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{
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++iter->count;
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iter->ts = _ts;
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return iter->data;
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}
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if (iter->count == 0)
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{
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++freeCount;
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if (iter->ts < mints)
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{
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mints = iter->ts;
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oldest = iter;
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}
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}
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}
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if (freeCount && (_blocks.size() >= CacheSize))
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{
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oldest->block = block;
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oldest->count = 1;
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oldest->ts = _ts;
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_device->read(block, oldest->data);
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return oldest->data;
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}
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auto_array<uint8_t> buffer(new uint8_t[512]);
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BlockDescriptor bd = { block, 1, _ts, buffer.get() };
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_device->read(block, buffer.get());
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_blocks.push_back(bd);
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return buffer.release();
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}
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void BlockCache::release(unsigned block)
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{
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for (BDIter iter = _blocks.begin(); iter != _blocks.end(); ++iter)
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{
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if (iter->block == block)
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{
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if (!--iter->count)
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{
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_device->write(block, iter->data);
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// trim back if too many entries.
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if (_blocks.size() > CacheSize)
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{
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delete[] iter->data;
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_blocks.erase(iter);
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}
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}
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return;
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}
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}
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} |