Block Pop() {
if (read_closed_) return Block();
Block b;
queue_.pop(b);
read_closed_ = !b.IsValid();
return b;
}
//! Return next block for BlockQueue, store into caching File and return it.
Block NextBlock() {
Block b = queue_->Pop();
// cache block in file_ (but not the termination block from the queue)
if (b.IsValid())
queue_->file_.AppendBlock(b);
return b;
}
