/**
* @brief Initializes the Disk Cache.
*
* When this is finished, all data is on disk, and the in-RAM cache
* is empty.
*
* @param element_count The number of data elements.
* @param cache_size_ The max number of data blocks to hold in RAM at once.
*/
void init(size_t element_count_, size_t cache_size_) {
block_count = (element_count_ / BLOCK_SIZE) + 1;
e_count = block_count * BLOCK_SIZE;
cache_size = cache_size_;
// Initialize vectors
cache.resize(cache_size * BLOCK_SIZE);
cache_info.resize(cache_size);
data_table.resize(block_count);
// Set all cache blocks to "not used"
for (size_t i=0; i < cache_size; i++) {
cache_info[i].priority = 0;
cache_info[i].modified = false;
cache_info[i].used = false;
}
// Clear out the data_table pointers
memset(&(data_table[0]), 0, sizeof(T*)*block_count);
// Initialize the disk cache file with the appropriate size
data_file.open();
data_file.seekp((sizeof(T)*e_count)-1);
data_file.put('\0');
data_file.flush();
}
/**
* Unloads a block from the cache, making sure that any modifications
* are written back to disk.
*/
void unload_cache_block(size_t cb_index) {
const size_t b_index = cache_info[cb_index].index;
// Clear the reference from the table
if (cache_info[cb_index].used)
data_table[b_index] = nullptr;
// Check if the cache block is modified, and if so, write it to disk
if (cache_info[cb_index].modified && cache_info[cb_index].used) {
// Seek to the correct place in the file
data_file.seekp(sizeof(T)*BLOCK_SIZE*b_index);
// Write out the data block
const T* i = &(cache[cb_index*BLOCK_SIZE]);
data_file.write((char*)i, sizeof(T)*BLOCK_SIZE);
// Clear modified tag
cache_info[cb_index].modified = false;
cache_info[cb_index].used = false;
}
// Set priority to zero
cache_info[cb_index].priority = 0;
}
