gistfile1.cpp

void NGramIndexReader::Find(const std::string &query,
                            SearchResults *results) {
  if (query.size() < ngram_size_) {
    FindSmall(query, results);
    return;
  }

  // split the query into its constituent ngrams
  std::set<std::string> ngrams;
  for (std::string::size_type i = 0;
       i <= query.length() - ngram_size_; i++) {
    ngrams.insert(query.substr(i, ngram_size_));
  }
  assert(!ngrams.empty());

  std::vector<std::thread> threads;
  std::size_t parallelism = std::thread::hardware_concurrency() + 1;
  threads.reserve(parallelism);

  auto it = shards_.begin();
  while (true) {
    // build up a vector of threads to do searches
    for (std::size_t i = 0; i < parallelism; i++) {
      SSTableReader *reader = *it;
      threads.push_back(std::thread(&NGramIndexReader::FindShard, this, query,
                                    ngrams, *reader, results));
      if (++it == shards_.end()) {
        break;
      }
    }
    for (std::size_t i = 0; i < threads.size(); i++) {
      threads[i].join();
    }
    if (results->IsFull() || it == shards_.end()) {
      break;
    }
    threads.clear();
  }
}