PinnedBlock KeepFileBlockSource::NextBlock() {
if (current_block_ >= file_.num_blocks() && fetching_blocks_.empty())
return PinnedBlock();
if (prefetch_size_ == 0)
{
// operate without prefetching
return NextUnpinnedBlock().PinWait(local_worker_id_);
}
else
{
// prefetch #desired bytes
while (fetching_bytes_ < prefetch_size_ &&
current_block_ < file_.num_blocks())
{
Block b = NextUnpinnedBlock();
fetching_bytes_ += b.size();
fetching_blocks_.emplace_back(b.Pin(local_worker_id_));
}
// this might block if the prefetching is not finished
PinnedBlock b = fetching_blocks_.front()->Wait();
fetching_bytes_ -= b.size();
fetching_blocks_.pop_front();
return b;
}
}
void KeepFileBlockSource::Prefetch(size_t prefetch_size) {
if (prefetch_size >= prefetch_size_) {
prefetch_size_ = prefetch_size;
// prefetch #desired bytes
while (fetching_bytes_ < prefetch_size_ &&
current_block_ < file_.num_blocks())
{
Block b = NextUnpinnedBlock();
fetching_bytes_ += b.size();
fetching_blocks_.emplace_back(b.Pin(local_worker_id_));
}
}
else if (prefetch_size < prefetch_size_) {
prefetch_size_ = prefetch_size;
// cannot discard prefetched Blocks
}
}
