//returns the number of doubles actually freed
size_t DiskBackedBlockMap::backup_and_free_doubles(size_t requested_doubles_to_free) {
size_t freed_count = 0;
try {
while (freed_count < requested_doubles_to_free) { //if requested_doubles_to_free <= 0, no iterations performed.
ServerBlock* block;
BlockId bid = policy_.get_next_block_for_removal(block);
block->wait();
ServerBlock* blk = block_map_.block(bid);
check(blk == block, "bug in free_doubles");
SIP_LOG(
std::cout << "S " << sip_mpi_attr_.company_rank() << " : Freeing block " << bid << " and writing to disk to make space for new block" << std::endl);
if (!blk->disk_state_.is_valid_on_disk()) {
write_block_to_disk(bid, blk);
blocks_to_disk_.inc();
blk->disk_state_.set_valid_on_disk();
}
double* data_to_free = blk->get_data();
free_data(data_to_free, blk->size()); //this method updates remaining_doubles_
blk->disk_state_.unset_in_memory();
blk->data_ = NULL;
freed_count += blk->size();
}
} catch (const std::out_of_range& oor) {
//ran out of blocks, just return what was freed.
}
return freed_count;
}
/** Template specialization for ServerBlock.
*
* Regular LRU Array policy is to evict the
* "first" block from the least recently used array.
* For ServerBlocks however, since they are not
* removed from the BlockMap, but are "emptied out",
* the regular array policy won't work.
*
* This methods first chooses an array whose block
* is to be evicted. It then finds one, skipping
* over those blocks which have been "emptied" out.
*/
template<> BlockId LRUArrayPolicy<ServerBlock>::get_next_block_for_removal(){
/** Return an arbitrary block from the least recently used array
*/
if(lru_list_.empty())
throw std::out_of_range("No blocks have been touched, yet block requested for flushing");
while (!lru_list_.empty()) {
int to_remove_array = lru_list_.back();
IdBlockMap<ServerBlock>::PerArrayMap* array_map = block_map_.per_array_map(to_remove_array);
IdBlockMap<ServerBlock>::PerArrayMap::iterator it = array_map->begin();
for (; it != array_map->end(); it ++) {
ServerBlock *blk = it->second;
if (blk !=NULL && blk->get_data() != NULL) {
return it->first;
}
}
lru_list_.pop_back();
}
throw std::out_of_range("No server blocks to remove - all empty or none present !");
}
