Cleaning up url_index_private_data and in_memory_url_index_types.

components/omnibox/browser/url_index_private_data.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/omnibox/browser/url_index_private_data.h"
 
 #include <stdint.h>
 
 #include <functional>
 #include <iterator>
@@ skipping 19 matching lines @@
 #include "components/omnibox/browser/in_memory_url_index.h"
 #include "components/search_engines/template_url_service.h"
 #include "components/url_formatter/url_formatter.h"
 
 #if defined(USE_SYSTEM_PROTOBUF)
 #include <google/protobuf/repeated_field.h>
 #else
 #include "third_party/protobuf/src/google/protobuf/repeated_field.h"
 #endif
 
+namespace {
+
 using google::protobuf::RepeatedField;
 using google::protobuf::RepeatedPtrField;
 using in_memory_url_index::InMemoryURLIndexCacheItem;
 
 typedef in_memory_url_index::InMemoryURLIndexCacheItem_WordListItem
     WordListItem;
 typedef in_memory_url_index::InMemoryURLIndexCacheItem_WordMapItem_WordMapEntry
     WordMapEntry;
 typedef in_memory_url_index::InMemoryURLIndexCacheItem_WordMapItem WordMapItem;
 typedef in_memory_url_index::InMemoryURLIndexCacheItem_CharWordMapItem
@@ skipping 12 matching lines @@
         HistoryInfoMapEntry;
 typedef in_memory_url_index::
     InMemoryURLIndexCacheItem_HistoryInfoMapItem_HistoryInfoMapEntry_VisitInfo
         HistoryInfoMapEntry_VisitInfo;
 typedef in_memory_url_index::InMemoryURLIndexCacheItem_WordStartsMapItem
     WordStartsMapItem;
 typedef in_memory_url_index::
     InMemoryURLIndexCacheItem_WordStartsMapItem_WordStartsMapEntry
         WordStartsMapEntry;
 
+// ContainerCast ---------------------------------------------------------------
+// A helper to Intersect algorithm that takes advantage of copy/move constructor
+// if the original and resulting sets type are the same.
+
+// ContainerTo has a constructor from ContainerFrom.
+template <typename ContainerTo, typename ContainerFrom>
+ContainerTo ContainerCastImpl(ContainerFrom&& cont, std::true_type) {
+  return ContainerTo(std::forward<ContainerFrom>(cont));
+}
+
+// ContainerTo does not have a constructor from ContainerFrom.
+template <typename ContainerTo, typename ContainerFrom>
+ContainerTo ContainerCastImpl(const ContainerFrom& cont, std::false_type) {
+  return ContainerTo(cont.begin(), cont.end());
+}
+
+// Type traits to disable perfect forwarding.
+template <typename T>
+using rvalue_t = typename std::add_rvalue_reference<
+    typename std::remove_reference<T>::type>::type;
+
+// ContainerTo does not have a constructor from ContainerFrom.
+// Note: we have to use remove_reference to disable perfect forwarding.
+template <typename ContainerTo, typename ContainerFrom>
+ContainerTo ContainerCastImpl(rvalue_t<ContainerFrom> cont, std::false_type) {
+  return ContainerTo(std::make_move_iterator(cont.begin()),
+                     std::make_move_iterator(cont.end()));
+}
+
+template <typename ContainerTo, typename ContainerFrom>
+ContainerTo ContinerCast(ContainerFrom&& cont) {

[Alexander Yashkin, 2017/02/21 07:07:15]

ContainerCast?

[dyaroshev, 2017/02/26 01:12:17]

Not applicable.

+  return ContainerCastImpl<ContainerTo>(
+      std::forward<ContainerFrom>(cont),
+      std::is_convertible<ContainerTo, ContainerFrom>{});
+}
+
 // Algorithm Functions ---------------------------------------------------------
 
 // Comparison function for sorting search terms by descending length.
 bool LengthGreater(const base::string16& string_a,
                    const base::string16& string_b) {
   return string_a.length() > string_b.length();
 }
 
+// Creates a new set by intersecting all the sets in range defined by |fist|,

[Alexander Yashkin, 2017/02/21 07:07:15]

Can you make this comment more human readable?
Whats the customization point? I am not sure every mere mortal knows whats it.

Until I saw how this function is used I could not figure what it was doing.
Maybe example would be useful?

I would prefer this function to be inlined in both places where its used instead
of having 
all the ContainerCast magic.

Peter, Mark?

[dyaroshev, 2017/02/22 22:57:25]

Another good argument for not inlining this -> this seems to be a bad way to
implement multiple sets intersect (still better than the previous one) - it
calls an allocator multiple times an does many unnecessary copies.

A good way could grow out of smth like this: https://godbolt.org/g/V67d6R - it's
definitely not inlinable. And if we put a method in an independent location, we
could easily improve it later and affect all the places of use.

[dyaroshev, 2017/02/23 00:45:54]

Significantly revised version: https://godbolt.org/g/vgCVmr

+// |last|. |get_set| is a customization point for getting the set from the
+// element of the range.
+template <typename ResultingSet, typename Iter, typename Projection>
+ResultingSet IntersectSetsWithProjection(Iter first,
+                                         Iter last,
+                                         Projection get_set) {
+  if (first == last)
+    return ResultingSet();
+
+  auto res = ContinerCast<ResultingSet>(get_set(*first));

[Peter Kasting, 2017/02/25 04:54:42]

It seems like the main reason you need ContainerCast is because one of the
callers is trying to supply a vector type for ResultingSet.

This sort of makes the type names and comments of this function a lie.  They
shouldn't explicitly say "set" if this is really just about working on arbitrary
containers.

But the other fix would be to intersect to a set, and then pull a vector out of
that at the end to return from the caller that wants to do so.  This would allow
removing all the ContainerCast stuff, which still seems like a desirable goal to
me in terms of lowering boilerplate and improving readability.  It's not
instantly obvious how it would affect efficiency, but it seems like it would
lower it slightly (but maybe not enough to matter).

[dyaroshev, 2017/02/26 01:12:16]

Since this is the cleaning up patch and I don't see a 100% satisfying solution -
I've reverted the intersect patch, created a task for writing a generic
union/intersect functions and added a todo. Is this ok?

[Peter Kasting, 2017/02/28 00:33:54]

It's fine.

+
+  // Like std::accumulate but short circuits if set is empty.
+  for (++first; first != last && !res.empty(); ++first)
+    res = base::STLSetIntersection<ResultingSet>(res, get_set(*first));
+
+  return res;
+}
+
+}  // namespace
 
 // UpdateRecentVisitsFromHistoryDBTask -----------------------------------------
 
 // HistoryDBTask used to update the recent visit data for a particular
 // row from the history database.
 class UpdateRecentVisitsFromHistoryDBTask : public history::HistoryDBTask {
  public:
   explicit UpdateRecentVisitsFromHistoryDBTask(
       URLIndexPrivateData* private_data,
       history::URLID url_id);
@@ skipping 97 matching lines @@
     // the index we need individual, lower-cased words, ignoring escapings. For
     // the final filtering we need whitespace separated substrings possibly
     // containing escaped characters.
     base::string16 lower_raw_string(base::i18n::ToLower(search_string));
     base::string16 lower_unescaped_string = net::UnescapeURLComponent(
         lower_raw_string,
         net::UnescapeRule::SPACES | net::UnescapeRule::PATH_SEPARATORS |
             net::UnescapeRule::URL_SPECIAL_CHARS_EXCEPT_PATH_SEPARATORS);
 
     // Extract individual 'words' (as opposed to 'terms'; see comment in
-    // HistoryIdSetToScoredMatches()) from the search string. When the user
+    // HistoryIdsToScoredMatches()) from the search string. When the user
     // types "colspec=ID%20Mstone Release" we get four 'words': "colspec", "id",
     // "mstone" and "release".
     String16Vector lower_words(
         String16VectorFromString16(lower_unescaped_string, false, nullptr));
     if (lower_words.empty())
       continue;
-    HistoryIDSet history_id_set = HistoryIDSetFromWords(lower_words);
-    pre_filter_item_count_ += history_id_set.size();
-    // Trim the candidate pool if it is large. Note that we do not filter out
-    // items that do not contain the search terms as proper substrings --
-    // doing so is the performance-costly operation we are trying to avoid in
-    // order to maintain omnibox responsiveness.
-    const size_t kItemsToScoreLimit = 500;
-    if (history_id_set.size() > kItemsToScoreLimit) {
-      HistoryIDVector history_ids;
-      std::copy(history_id_set.begin(), history_id_set.end(),
-                std::back_inserter(history_ids));
-      // Trim down the set by sorting by typed-count, visit-count, and last
-      // visit.
-      HistoryItemFactorGreater item_factor_functor(history_info_map_);
-      std::partial_sort(history_ids.begin(),
-                        history_ids.begin() + kItemsToScoreLimit,
-                        history_ids.end(), item_factor_functor);
-      history_id_set.clear();
-      std::copy(history_ids.begin(), history_ids.begin() + kItemsToScoreLimit,
-                std::inserter(history_id_set, history_id_set.end()));
-      post_filter_item_count_ += history_id_set.size();
-    } else {
-      post_filter_item_count_ += pre_filter_item_count_;
-    }
+
+    HistoryIDVector history_ids = HistoryIDsFromWords(lower_words);
+
+    pre_filter_item_count_ += history_ids.size();
+    TrimHistoryIdsPool(&history_ids);
+    post_filter_item_count_ += history_ids.size();
+
     ScoredHistoryMatches temp_scored_items;
-    HistoryIdSetToScoredMatches(history_id_set, lower_raw_string,
-                                template_url_service, bookmark_model,
-                                &temp_scored_items);
+    HistoryIdsToScoredMatches(std::move(history_ids), lower_raw_string,
+                              template_url_service, bookmark_model,
+                              &temp_scored_items);
     scored_items.insert(scored_items.end(), temp_scored_items.begin(),
                         temp_scored_items.end());
   }
   // Select and sort only the top |max_matches| results.
   if (scored_items.size() > max_matches) {
     std::partial_sort(scored_items.begin(), scored_items.begin() + max_matches,
                       scored_items.end(),
                       ScoredHistoryMatch::MatchScoreGreater);
     scored_items.resize(max_matches);
   } else {
@@ skipping 235 matching lines @@
   //    post_scoring_item_count_
 }
 
 bool URLIndexPrivateData::Empty() const {
   return history_info_map_.empty();
 }
 
 void URLIndexPrivateData::Clear() {
   last_time_rebuilt_from_history_ = base::Time();
   word_list_.clear();
-  available_words_.clear();
+  available_words_ = {};
   word_map_.clear();
   char_word_map_.clear();
   word_id_history_map_.clear();
   history_id_word_map_.clear();
   history_info_map_.clear();
   word_starts_map_.clear();
 }
 
 URLIndexPrivateData::~URLIndexPrivateData() {}
 
-HistoryIDSet URLIndexPrivateData::HistoryIDSetFromWords(
+HistoryIDVector URLIndexPrivateData::HistoryIDsFromWords(
     const String16Vector& unsorted_words) {
+  // The name of the histogram wasn't changed to HistoryIdsFromWords to preserve
+  // old data valid.

[Peter Kasting, 2017/02/25 04:54:41]

Nit: Sounds like we're leaving the old name.  If so I'd just say: "This
histogram name reflects the historic name of this function."

[dyaroshev, 2017/02/26 01:12:16]

Done.

   SCOPED_UMA_HISTOGRAM_TIMER("Omnibox.HistoryQuickHistoryIDSetFromWords");
   // Break the terms down into individual terms (words), get the candidate
   // set for each term, and intersect each to get a final candidate list.
   // Note that a single 'term' from the user's perspective might be
   // a string like "http://www.somewebsite.com" which, from our perspective,
   // is four words: 'http', 'www', 'somewebsite', and 'com'.
-  HistoryIDSet history_id_set;
   String16Vector words(unsorted_words);
   // Sort the words into the longest first as such are likely to narrow down
   // the results quicker. Also, single character words are the most expensive
   // to process so save them for last.
   std::sort(words.begin(), words.end(), LengthGreater);
-  for (String16Vector::iterator iter = words.begin(); iter != words.end();
-       ++iter) {
-    base::string16 uni_word = *iter;
-    HistoryIDSet term_history_set = HistoryIDsForTerm(uni_word);
-    if (term_history_set.empty()) {
-      history_id_set.clear();
-      break;
-    }
-    if (iter == words.begin()) {
-      history_id_set.swap(term_history_set);
-    } else {
-      HistoryIDSet new_history_id_set = base::STLSetIntersection<HistoryIDSet>(
-          history_id_set, term_history_set);
-      history_id_set.swap(new_history_id_set);
-    }
-  }
-  return history_id_set;
+
+  return IntersectSetsWithProjection<HistoryIDVector>(
+      words.begin(), words.end(),
+      [this](const base::string16& word) { return HistoryIDsForTerm(word); });
+}
+
+void URLIndexPrivateData::TrimHistoryIdsPool(
+    HistoryIDVector* history_ids) const {
+  constexpr size_t kItemsToScoreLimit = 500;
+  if (history_ids->size() < kItemsToScoreLimit)
+    return;
+
+  // Trim down the set by sorting by typed-count, visit-count, and last
+  // visit.
+  auto new_end = history_ids->begin() + kItemsToScoreLimit;
+  HistoryItemFactorGreater item_factor_functor(history_info_map_);
+
+  std::nth_element(history_ids->begin(), new_end, history_ids->end(),
+                   item_factor_functor);
+  history_ids->erase(new_end, history_ids->end());
 }
 
 HistoryIDSet URLIndexPrivateData::HistoryIDsForTerm(
     const base::string16& term) {
   if (term.empty())
     return HistoryIDSet();
 
   // TODO(mrossetti): Consider optimizing for very common terms such as
   // 'http[s]', 'www', 'com', etc. Or collect the top 100 more frequently
   // occuring words in the user's searches.
@@ skipping 46 matching lines @@
 
     // Reduce the word set with any leftover, unprocessed characters.
     if (!unique_chars.empty()) {
       WordIDSet leftover_set(WordIDSetForTermChars(unique_chars));
       // We might come up empty on the leftovers.
       if (leftover_set.empty()) {
         search_term_cache_[term] = SearchTermCacheItem();
         return HistoryIDSet();
       }
       // Or there may not have been a prefix from which to start.
-      if (prefix_chars.empty()) {
-        word_id_set.swap(leftover_set);
-      } else {
-        WordIDSet new_word_id_set = base::STLSetIntersection<WordIDSet>(
-            word_id_set, leftover_set);
-        word_id_set.swap(new_word_id_set);
-      }
+      word_id_set = prefix_chars.empty() ? std::move(leftover_set)
+                                         : base::STLSetIntersection<WordIDSet>(
+                                               word_id_set, leftover_set);
     }
 
     // We must filter the word list because the resulting word set surely
     // contains words which do not have the search term as a proper subset.
     for (WordIDSet::iterator word_set_iter = word_id_set.begin();
          word_set_iter != word_id_set.end(); ) {
       if (word_list_[*word_set_iter].find(term) == base::string16::npos)
         word_set_iter = word_id_set.erase(word_set_iter);
       else
         ++word_set_iter;
     }
   } else {
     word_id_set = WordIDSetForTermChars(Char16SetFromString16(term));
   }
 
   // If any words resulted then we can compose a set of history IDs by unioning
   // the sets from each word.
   HistoryIDSet history_id_set;
-  if (!word_id_set.empty()) {
-    for (WordIDSet::iterator word_id_iter = word_id_set.begin();
-         word_id_iter != word_id_set.end(); ++word_id_iter) {
-      WordID word_id = *word_id_iter;
-      WordIDHistoryMap::iterator word_iter = word_id_history_map_.find(word_id);
-      if (word_iter != word_id_history_map_.end()) {
-        HistoryIDSet& word_history_id_set(word_iter->second);
-        history_id_set.insert(word_history_id_set.begin(),
-                              word_history_id_set.end());
-      }
+  for (WordID word_id : word_id_set) {
+    WordIDHistoryMap::iterator word_iter = word_id_history_map_.find(word_id);
+    if (word_iter != word_id_history_map_.end()) {
+      HistoryIDSet& word_history_id_set(word_iter->second);
+      history_id_set.insert(word_history_id_set.begin(),
+                            word_history_id_set.end());
     }
   }
 
   // Record a new cache entry for this word if the term is longer than
   // a single character.
   if (term_length > 1)
     search_term_cache_[term] = SearchTermCacheItem(word_id_set, history_id_set);
 
   return history_id_set;
 }
 
 WordIDSet URLIndexPrivateData::WordIDSetForTermChars(
     const Char16Set& term_chars) {
-  WordIDSet word_id_set;
-  for (Char16Set::const_iterator c_iter = term_chars.begin();
-       c_iter != term_chars.end(); ++c_iter) {
-    CharWordIDMap::iterator char_iter = char_word_map_.find(*c_iter);
-    if (char_iter == char_word_map_.end()) {
-      // A character was not found so there are no matching results: bail.
-      word_id_set.clear();
-      break;
-    }
-    WordIDSet& char_word_id_set(char_iter->second);
-    // It is possible for there to no longer be any words associated with
-    // a particular character. Give up in that case.
-    if (char_word_id_set.empty()) {
-      word_id_set.clear();
-      break;
-    }
-
-    if (c_iter == term_chars.begin()) {
-      // First character results becomes base set of results.
-      word_id_set = char_word_id_set;
-    } else {
-      // Subsequent character results get intersected in.
-      WordIDSet new_word_id_set = base::STLSetIntersection<WordIDSet>(
-          word_id_set, char_word_id_set);
-      word_id_set.swap(new_word_id_set);
-    }
-  }
-  return word_id_set;
+  WordIDSet empty_set;
+  auto GetSet = [&](base::char16 c) -> const WordIDSet& {

[Peter Kasting, 2017/02/25 04:54:42]

Nit: I would explicitly capture [this, &empty_set].

That said; can you return the set by value and not const ref, and avoid
declaring |empty_set| at all (just return WordIDSet() in the lambda)?

[dyaroshev, 2017/02/26 01:12:17]

Not applicable.

Returning by value would add an extra copy which can be expensive.

[Peter Kasting, 2017/02/26 01:35:18]

True.  But is it expensive enough to matter?

One of the themes of my review comments should be taken to be "use simpler and
more readable forms when the performance difference has little practical
effect".  I honestly don't know the answer here, that's just my general guidance
for the future.

[dyaroshev, 2017/02/26 01:39:16]

Well, for std::set I've seen cases where it does. I agree with the general
guidance. 

+    auto char_iter = char_word_map_.find(c);
+    if (char_iter == char_word_map_.end())
+      return empty_set;
+    return char_iter->second;

[Peter Kasting, 2017/02/25 04:54:41]

Nit: Simpler:

    return char_iter == char_word_map_.end() ? empty_set : char_iter->second;

[dyaroshev, 2017/02/26 01:12:16]

Not applicable.

+  };
+  return IntersectSetsWithProjection<WordIDSet>(term_chars.begin(),
+                                                term_chars.end(), GetSet);
 }
 
-void URLIndexPrivateData::HistoryIdSetToScoredMatches(
-    HistoryIDSet history_id_set,
+void URLIndexPrivateData::HistoryIdsToScoredMatches(
+    HistoryIDVector history_ids,
     const base::string16& lower_raw_string,
     const TemplateURLService* template_url_service,
     bookmarks::BookmarkModel* bookmark_model,
     ScoredHistoryMatches* scored_items) const {
-  if (history_id_set.empty())
+  if (history_ids.empty())
     return;
 
   // Break up the raw search string (complete with escaped URL elements) into
   // 'terms' (as opposed to 'words'; see comment in HistoryItemsForTerms()).
   // We only want to break up the search string on 'true' whitespace rather than
   // escaped whitespace.  For example, when the user types
   // "colspec=ID%20Mstone Release" we get two 'terms': "colspec=id%20mstone" and
   // "release".
   String16Vector lower_raw_terms =
       base::SplitString(lower_raw_string, base::kWhitespaceUTF16,
                         base::KEEP_WHITESPACE, base::SPLIT_WANT_NONEMPTY);
 
   // Don't score matches when there are no terms to score against.  (It's
   // possible that the word break iterater that extracts words to search for in
   // the database allows some whitespace "words" whereas SplitString excludes a
   // long list of whitespace.)  One could write a scoring function that gives a
   // reasonable order to matches when there are no terms (i.e., all the words
   // are some form of whitespace), but this is such a rare edge case that it's
   // not worth the time.
   if (lower_raw_terms.empty())
     return;
 
   WordStarts lower_terms_to_word_starts_offsets;
   CalculateWordStartsOffsets(lower_raw_terms,
                              &lower_terms_to_word_starts_offsets);
 
   // Filter bad matches and other matches we don't want to display.
-  for (auto it = history_id_set.begin();;) {
-    it = std::find_if(it, history_id_set.end(),
-                      [this, template_url_service](const HistoryID history_id) {
-                        return ShouldFilter(history_id, template_url_service);
-                      });
-    if (it == history_id_set.end())
-      break;
-    it = history_id_set.erase(it);
+  {

[Peter Kasting, 2017/02/25 04:54:42]

Nit: {} not necessary

[dyaroshev, 2017/02/26 01:12:16]

Done.

+    auto filter = [this, template_url_service](const HistoryID history_id) {
+      return ShouldFilter(history_id, template_url_service);
+    };
+    history_ids.erase(
+        std::remove_if(history_ids.begin(), history_ids.end(), filter),
+        history_ids.end());
   }
 
   // Score the matches.
-  const size_t num_matches = history_id_set.size();
+  const size_t num_matches = history_ids.size();
   const base::Time now = base::Time::Now();
   std::transform(
-      history_id_set.begin(), history_id_set.end(),
-      std::back_inserter(*scored_items), [&](const HistoryID history_id) {
+      history_ids.begin(), history_ids.end(), std::back_inserter(*scored_items),
+      [&](const HistoryID history_id) {
         auto hist_pos = history_info_map_.find(history_id);
         const history::URLRow& hist_item = hist_pos->second.url_row;
         auto starts_pos = word_starts_map_.find(history_id);
         DCHECK(starts_pos != word_starts_map_.end());
         return ScoredHistoryMatch(
             hist_item, hist_pos->second.visits, lower_raw_string,
             lower_raw_terms, lower_terms_to_word_starts_offsets,
             starts_pos->second,
             bookmark_model && bookmark_model->IsBookmarked(hist_item.url()),
             num_matches, now);
@@ skipping 90 matching lines @@
   HistoryID history_id = static_cast<HistoryID>(row.id());
   // Split URL into individual, unique words then add in the title words.
   const GURL& gurl(row.url());
   const base::string16& url =
       bookmarks::CleanUpUrlForMatching(gurl, nullptr);
   String16Set url_words = String16SetFromString16(url,
       word_starts ? &word_starts->url_word_starts_ : nullptr);
   const base::string16& title = bookmarks::CleanUpTitleForMatching(row.title());
   String16Set title_words = String16SetFromString16(title,
       word_starts ? &word_starts->title_word_starts_ : nullptr);
-  String16Set words = base::STLSetUnion<String16Set>(url_words, title_words);
-  for (String16Set::iterator word_iter = words.begin();
-       word_iter != words.end(); ++word_iter)
-    AddWordToIndex(*word_iter, history_id);
+  for (const auto& word :
+       base::STLSetUnion<String16Set>(url_words, title_words))
+    AddWordToIndex(word, history_id);
 
   search_term_cache_.clear();  // Invalidate the term cache.
 }
 
 void URLIndexPrivateData::AddWordToIndex(const base::string16& term,
                                          HistoryID history_id) {
-  WordMap::iterator word_pos = word_map_.find(term);
-  if (word_pos != word_map_.end())
-    UpdateWordHistory(word_pos->second, history_id);
-  else
-    AddWordHistory(term, history_id);
+  WordMap::iterator word_pos;
+  bool is_new;
+  std::tie(word_pos, is_new) = word_map_.emplace(term, WordID());
+
+  // Adding a new word (i.e. a word that is not already in the word index).
+  if (is_new) {
+    word_pos->second = AddNewWordToWordList(term);
+
+    // For each character in the newly added word add the word to the character
+    // index.
+    for (base::char16 uni_char : Char16SetFromString16(term))
+      char_word_map_[uni_char].insert(word_pos->second);
+  }
+
+  word_id_history_map_[word_pos->second].insert(history_id);
+  history_id_word_map_[history_id].insert(word_pos->second);
 }
 
-void URLIndexPrivateData::AddWordHistory(const base::string16& term,
-                                         HistoryID history_id) {
+WordID URLIndexPrivateData::AddNewWordToWordList(const base::string16& term) {
   WordID word_id = word_list_.size();
   if (available_words_.empty()) {
     word_list_.push_back(term);
-  } else {
-    word_id = *(available_words_.begin());
-    word_list_[word_id] = term;
-    available_words_.erase(word_id);
+    return word_id;
   }
-  word_map_[term] = word_id;
 
-  HistoryIDSet history_id_set;
-  history_id_set.insert(history_id);
-  word_id_history_map_[word_id] = history_id_set;
-  AddToHistoryIDWordMap(history_id, word_id);
-
-  // For each character in the newly added word (i.e. a word that is not
-  // already in the word index), add the word to the character index.
-  Char16Set characters = Char16SetFromString16(term);
-  for (Char16Set::iterator uni_char_iter = characters.begin();
-       uni_char_iter != characters.end(); ++uni_char_iter) {
-    base::char16 uni_char = *uni_char_iter;
-    CharWordIDMap::iterator char_iter = char_word_map_.find(uni_char);
-    if (char_iter != char_word_map_.end()) {
-      // Update existing entry in the char/word index.
-      WordIDSet& word_id_set(char_iter->second);
-      word_id_set.insert(word_id);
-    } else {
-      // Create a new entry in the char/word index.
-      WordIDSet word_id_set;
-      word_id_set.insert(word_id);
-      char_word_map_[uni_char] = word_id_set;
-    }
-  }
-}
-
-void URLIndexPrivateData::UpdateWordHistory(WordID word_id,
-                                            HistoryID history_id) {
-  WordIDHistoryMap::iterator history_pos = word_id_history_map_.find(word_id);
-  DCHECK(history_pos != word_id_history_map_.end());
-  HistoryIDSet& history_id_set(history_pos->second);
-  history_id_set.insert(history_id);
-  AddToHistoryIDWordMap(history_id, word_id);
-}
-
-void URLIndexPrivateData::AddToHistoryIDWordMap(HistoryID history_id,
-                                                WordID word_id) {
-  HistoryIDWordMap::iterator iter = history_id_word_map_.find(history_id);
-  if (iter != history_id_word_map_.end()) {
-    WordIDSet& word_id_set(iter->second);
-    word_id_set.insert(word_id);
-  } else {
-    WordIDSet word_id_set;
-    word_id_set.insert(word_id);
-    history_id_word_map_[history_id] = word_id_set;
-  }
+  word_id = available_words_.top();
+  available_words_.pop();
+  word_list_[word_id] = term;
+  return word_id;
 }
 
 void URLIndexPrivateData::RemoveRowFromIndex(const history::URLRow& row) {
   RemoveRowWordsFromIndex(row);
   HistoryID history_id = static_cast<HistoryID>(row.id());
   history_info_map_.erase(history_id);
   word_starts_map_.erase(history_id);
 }
 
 void URLIndexPrivateData::RemoveRowWordsFromIndex(const history::URLRow& row) {
   // Remove the entries in history_id_word_map_ and word_id_history_map_ for
   // this row.
   HistoryID history_id = static_cast<HistoryID>(row.id());
   WordIDSet word_id_set = history_id_word_map_[history_id];
   history_id_word_map_.erase(history_id);
 
   // Reconcile any changes to word usage.
-  for (WordIDSet::iterator word_id_iter = word_id_set.begin();
-       word_id_iter != word_id_set.end(); ++word_id_iter) {
-    WordID word_id = *word_id_iter;
-    word_id_history_map_[word_id].erase(history_id);
-    if (!word_id_history_map_[word_id].empty())
-      continue;  // The word is still in use.
+  for (WordID word_id : word_id_set) {
+    auto word_id_history_map_iter = word_id_history_map_.find(word_id);
+    DCHECK(word_id_history_map_iter != word_id_history_map_.end());
+
+    word_id_history_map_iter->second.erase(history_id);
+    if (!word_id_history_map_iter->second.empty())
+      continue;
 
     // The word is no longer in use. Reconcile any changes to character usage.
     base::string16 word = word_list_[word_id];
-    Char16Set characters = Char16SetFromString16(word);
-    for (Char16Set::iterator uni_char_iter = characters.begin();
-         uni_char_iter != characters.end(); ++uni_char_iter) {
-      base::char16 uni_char = *uni_char_iter;
-      char_word_map_[uni_char].erase(word_id);
-      if (char_word_map_[uni_char].empty())
-        char_word_map_.erase(uni_char);  // No longer in use.
+    for (base::char16 uni_char : Char16SetFromString16(word)) {
+      auto char_word_map_iter = char_word_map_.find(uni_char);
+      char_word_map_iter->second.erase(word_id);
+      if (char_word_map_iter->second.empty())
+        char_word_map_.erase(char_word_map_iter);
     }
 
     // Complete the removal of references to the word.
-    word_id_history_map_.erase(word_id);
+    word_id_history_map_.erase(word_id_history_map_iter);
     word_map_.erase(word);
     word_list_[word_id] = base::string16();
-    available_words_.insert(word_id);
+    available_words_.push(word_id);
   }
 }
 
 void URLIndexPrivateData::ResetSearchTermCache() {
-  for (SearchTermCacheMap::iterator iter = search_term_cache_.begin();
-       iter != search_term_cache_.end(); ++iter)
-    iter->second.used_ = false;
+  for (auto& item : search_term_cache_)
+    item.second.used_ = false;
 }
 
 bool URLIndexPrivateData::SaveToFile(const base::FilePath& file_path) {
   base::TimeTicks beginning_time = base::TimeTicks::Now();
   InMemoryURLIndexCacheItem index_cache;
   SavePrivateData(&index_cache);
   std::string data;
   if (!index_cache.SerializeToString(&data)) {
     LOG(WARNING) << "Failed to serialize the InMemoryURLIndex cache.";
     return false;
@@ skipping 24 matching lines @@
   SaveWordIDHistoryMap(cache);
   SaveHistoryInfoMap(cache);
   SaveWordStartsMap(cache);
 }
 
 void URLIndexPrivateData::SaveWordList(InMemoryURLIndexCacheItem* cache) const {
   if (word_list_.empty())
     return;
   WordListItem* list_item = cache->mutable_word_list();
   list_item->set_word_count(word_list_.size());
-  for (String16Vector::const_iterator iter = word_list_.begin();
-       iter != word_list_.end(); ++iter)
-    list_item->add_word(base::UTF16ToUTF8(*iter));
+  for (const base::string16& word : word_list_)
+    list_item->add_word(base::UTF16ToUTF8(word));
 }
 
 void URLIndexPrivateData::SaveWordMap(InMemoryURLIndexCacheItem* cache) const {
   if (word_map_.empty())
     return;
   WordMapItem* map_item = cache->mutable_word_map();
   map_item->set_item_count(word_map_.size());
-  for (WordMap::const_iterator iter = word_map_.begin();
-       iter != word_map_.end(); ++iter) {
+  for (const auto& elem : word_map_) {
     WordMapEntry* map_entry = map_item->add_word_map_entry();
-    map_entry->set_word(base::UTF16ToUTF8(iter->first));
-    map_entry->set_word_id(iter->second);
+    map_entry->set_word(base::UTF16ToUTF8(elem.first));
+    map_entry->set_word_id(elem.second);
   }
 }
 
 void URLIndexPrivateData::SaveCharWordMap(
     InMemoryURLIndexCacheItem* cache) const {
   if (char_word_map_.empty())
     return;
   CharWordMapItem* map_item = cache->mutable_char_word_map();
   map_item->set_item_count(char_word_map_.size());
-  for (CharWordIDMap::const_iterator iter = char_word_map_.begin();
-       iter != char_word_map_.end(); ++iter) {
+  for (const auto& entry : char_word_map_) {
     CharWordMapEntry* map_entry = map_item->add_char_word_map_entry();
-    map_entry->set_char_16(iter->first);
-    const WordIDSet& word_id_set(iter->second);
+    map_entry->set_char_16(entry.first);
+    const WordIDSet& word_id_set(entry.second);
     map_entry->set_item_count(word_id_set.size());
-    for (WordIDSet::const_iterator set_iter = word_id_set.begin();
-         set_iter != word_id_set.end(); ++set_iter)
-      map_entry->add_word_id(*set_iter);
+    for (WordID word_id : word_id_set)
+      map_entry->add_word_id(word_id);
   }
 }
 
 void URLIndexPrivateData::SaveWordIDHistoryMap(
     InMemoryURLIndexCacheItem* cache) const {
   if (word_id_history_map_.empty())
     return;
   WordIDHistoryMapItem* map_item = cache->mutable_word_id_history_map();
   map_item->set_item_count(word_id_history_map_.size());
-  for (WordIDHistoryMap::const_iterator iter = word_id_history_map_.begin();
-       iter != word_id_history_map_.end(); ++iter) {
+  for (const auto& entry : word_id_history_map_) {
     WordIDHistoryMapEntry* map_entry =
         map_item->add_word_id_history_map_entry();
-    map_entry->set_word_id(iter->first);
-    const HistoryIDSet& history_id_set(iter->second);
+    map_entry->set_word_id(entry.first);
+    const HistoryIDSet& history_id_set(entry.second);
     map_entry->set_item_count(history_id_set.size());
-    for (HistoryIDSet::const_iterator set_iter = history_id_set.begin();
-         set_iter != history_id_set.end(); ++set_iter)
-      map_entry->add_history_id(*set_iter);
+    for (HistoryID history_id : history_id_set)
+      map_entry->add_history_id(history_id);
   }
 }
 
 void URLIndexPrivateData::SaveHistoryInfoMap(
     InMemoryURLIndexCacheItem* cache) const {
   if (history_info_map_.empty())
     return;
   HistoryInfoMapItem* map_item = cache->mutable_history_info_map();
   map_item->set_item_count(history_info_map_.size());
-  for (HistoryInfoMap::const_iterator iter = history_info_map_.begin();
-       iter != history_info_map_.end(); ++iter) {
+  for (const auto& entry : history_info_map_) {
     HistoryInfoMapEntry* map_entry = map_item->add_history_info_map_entry();
-    map_entry->set_history_id(iter->first);
-    const history::URLRow& url_row(iter->second.url_row);
+    map_entry->set_history_id(entry.first);
+    const history::URLRow& url_row(entry.second.url_row);
     // Note: We only save information that contributes to the index so there
     // is no need to save search_term_cache_ (not persistent).
     map_entry->set_visit_count(url_row.visit_count());
     map_entry->set_typed_count(url_row.typed_count());
     map_entry->set_last_visit(url_row.last_visit().ToInternalValue());
     map_entry->set_url(url_row.url().spec());
     map_entry->set_title(base::UTF16ToUTF8(url_row.title()));
-    const VisitInfoVector& visits(iter->second.visits);
-    for (VisitInfoVector::const_iterator visit_iter = visits.begin();
-         visit_iter != visits.end(); ++visit_iter) {
+    for (const auto& visit : entry.second.visits) {
       HistoryInfoMapEntry_VisitInfo* visit_info = map_entry->add_visits();
-      visit_info->set_visit_time(visit_iter->first.ToInternalValue());
-      visit_info->set_transition_type(visit_iter->second);
+      visit_info->set_visit_time(visit.first.ToInternalValue());
+      visit_info->set_transition_type(visit.second);
     }
   }
 }
 
 void URLIndexPrivateData::SaveWordStartsMap(
     InMemoryURLIndexCacheItem* cache) const {
   if (word_starts_map_.empty())
     return;
   // For unit testing: Enable saving of the cache as an earlier version to
   // allow testing of cache file upgrading in ReadFromFile().
   // TODO(mrossetti): Instead of intruding on production code with this kind of
   // test harness, save a copy of an older version cache with known results.
   // Implement this when switching the caching over to SQLite.
   if (saved_cache_version_ < 1)
     return;
 
   WordStartsMapItem* map_item = cache->mutable_word_starts_map();
   map_item->set_item_count(word_starts_map_.size());
-  for (WordStartsMap::const_iterator iter = word_starts_map_.begin();
-       iter != word_starts_map_.end(); ++iter) {
+  for (const auto& entry : word_starts_map_) {
     WordStartsMapEntry* map_entry = map_item->add_word_starts_map_entry();
-    map_entry->set_history_id(iter->first);
-    const RowWordStarts& word_starts(iter->second);
-    for (WordStarts::const_iterator i = word_starts.url_word_starts_.begin();
-         i != word_starts.url_word_starts_.end(); ++i)
-      map_entry->add_url_word_starts(*i);
-    for (WordStarts::const_iterator i = word_starts.title_word_starts_.begin();
-         i != word_starts.title_word_starts_.end(); ++i)
-      map_entry->add_title_word_starts(*i);
+    map_entry->set_history_id(entry.first);
+    const RowWordStarts& word_starts(entry.second);
+    for (auto url_word_start : word_starts.url_word_starts_)
+      map_entry->add_url_word_starts(url_word_start);
+    for (auto title_word_start : word_starts.title_word_starts_)
+      map_entry->add_title_word_starts(title_word_start);
   }
 }
 
 bool URLIndexPrivateData::RestorePrivateData(
     const InMemoryURLIndexCacheItem& cache) {
   last_time_rebuilt_from_history_ =
       base::Time::FromInternalValue(cache.last_rebuild_timestamp());
   const base::TimeDelta rebuilt_ago =
       base::Time::Now() - last_time_rebuilt_from_history_;
   if ((rebuilt_ago > base::TimeDelta::FromDays(7)) ||
@@ skipping 22 matching lines @@
 bool URLIndexPrivateData::RestoreWordList(
     const InMemoryURLIndexCacheItem& cache) {
   if (!cache.has_word_list())
     return false;
   const WordListItem& list_item(cache.word_list());
   uint32_t expected_item_count = list_item.word_count();
   uint32_t actual_item_count = list_item.word_size();
   if (actual_item_count == 0 || actual_item_count != expected_item_count)
     return false;
   const RepeatedPtrField<std::string>& words(list_item.word());
-  for (RepeatedPtrField<std::string>::const_iterator iter = words.begin();
-       iter != words.end(); ++iter)
-    word_list_.push_back(base::UTF8ToUTF16(*iter));
+  word_list_.reserve(words.size());
+  std::transform(
+      words.begin(), words.end(), std::back_inserter(word_list_),
+      [](const std::string& word) { return base::UTF8ToUTF16(word); });
   return true;
 }
 
 bool URLIndexPrivateData::RestoreWordMap(
     const InMemoryURLIndexCacheItem& cache) {
   if (!cache.has_word_map())
     return false;
   const WordMapItem& list_item(cache.word_map());
   uint32_t expected_item_count = list_item.item_count();
   uint32_t actual_item_count = list_item.word_map_entry_size();
   if (actual_item_count == 0 || actual_item_count != expected_item_count)
     return false;
-  const RepeatedPtrField<WordMapEntry>& entries(list_item.word_map_entry());
-  for (RepeatedPtrField<WordMapEntry>::const_iterator iter = entries.begin();
-       iter != entries.end(); ++iter)
-    word_map_[base::UTF8ToUTF16(iter->word())] = iter->word_id();
+  for (const auto& entry : list_item.word_map_entry())
+    word_map_[base::UTF8ToUTF16(entry.word())] = entry.word_id();
+
   return true;
 }
 
 bool URLIndexPrivateData::RestoreCharWordMap(
     const InMemoryURLIndexCacheItem& cache) {
   if (!cache.has_char_word_map())
     return false;
   const CharWordMapItem& list_item(cache.char_word_map());
   uint32_t expected_item_count = list_item.item_count();
   uint32_t actual_item_count = list_item.char_word_map_entry_size();
   if (actual_item_count == 0 || actual_item_count != expected_item_count)
     return false;
-  const RepeatedPtrField<CharWordMapEntry>&
-      entries(list_item.char_word_map_entry());
-  for (RepeatedPtrField<CharWordMapEntry>::const_iterator iter =
-       entries.begin(); iter != entries.end(); ++iter) {
-    expected_item_count = iter->item_count();
-    actual_item_count = iter->word_id_size();
+
+  for (const auto& entry : list_item.char_word_map_entry()) {
+    expected_item_count = entry.item_count();
+    actual_item_count = entry.word_id_size();
     if (actual_item_count == 0 || actual_item_count != expected_item_count)
       return false;
-    base::char16 uni_char = static_cast<base::char16>(iter->char_16());
-    WordIDSet word_id_set;
-    const RepeatedField<int32_t>& word_ids(iter->word_id());
-    for (RepeatedField<int32_t>::const_iterator jiter = word_ids.begin();
-         jiter != word_ids.end(); ++jiter)
-      word_id_set.insert(*jiter);
-    char_word_map_[uni_char] = word_id_set;
+    base::char16 uni_char = static_cast<base::char16>(entry.char_16());
+    const RepeatedField<int32_t>& word_ids(entry.word_id());

[Peter Kasting, 2017/02/25 04:54:41]

Nit: Use = rather than () to init references like this (multiple places)

[dyaroshev, 2017/02/26 01:12:16]

Done.

+    char_word_map_[uni_char] = {word_ids.begin(), word_ids.end()};
   }
   return true;
 }
 
 bool URLIndexPrivateData::RestoreWordIDHistoryMap(
     const InMemoryURLIndexCacheItem& cache) {
   if (!cache.has_word_id_history_map())
     return false;
   const WordIDHistoryMapItem& list_item(cache.word_id_history_map());
   uint32_t expected_item_count = list_item.item_count();
   uint32_t actual_item_count = list_item.word_id_history_map_entry_size();
   if (actual_item_count == 0 || actual_item_count != expected_item_count)
     return false;
-  const RepeatedPtrField<WordIDHistoryMapEntry>&
-      entries(list_item.word_id_history_map_entry());
-  for (RepeatedPtrField<WordIDHistoryMapEntry>::const_iterator iter =
-       entries.begin(); iter != entries.end(); ++iter) {
-    expected_item_count = iter->item_count();
-    actual_item_count = iter->history_id_size();
+  for (const auto& entry : list_item.word_id_history_map_entry()) {
+    expected_item_count = entry.item_count();
+    actual_item_count = entry.history_id_size();
     if (actual_item_count == 0 || actual_item_count != expected_item_count)
       return false;
-    WordID word_id = iter->word_id();
-    HistoryIDSet history_id_set;
-    const RepeatedField<int64_t>& history_ids(iter->history_id());
-    for (RepeatedField<int64_t>::const_iterator jiter = history_ids.begin();
-         jiter != history_ids.end(); ++jiter) {
-      history_id_set.insert(*jiter);
-      AddToHistoryIDWordMap(*jiter, word_id);
-    }
-    word_id_history_map_[word_id] = history_id_set;
+    WordID word_id = entry.word_id();
+    const RepeatedField<int64_t>& history_ids(entry.history_id());
+    word_id_history_map_[word_id] = {history_ids.begin(), history_ids.end()};
+    for (HistoryID history_id : history_ids)
+      history_id_word_map_[history_id].insert(word_id);
   }
   return true;
 }
 
 bool URLIndexPrivateData::RestoreHistoryInfoMap(
     const InMemoryURLIndexCacheItem& cache) {
   if (!cache.has_history_info_map())
     return false;
   const HistoryInfoMapItem& list_item(cache.history_info_map());
   uint32_t expected_item_count = list_item.item_count();
   uint32_t actual_item_count = list_item.history_info_map_entry_size();
   if (actual_item_count == 0 || actual_item_count != expected_item_count)
     return false;
-  const RepeatedPtrField<HistoryInfoMapEntry>&
-      entries(list_item.history_info_map_entry());
-  for (RepeatedPtrField<HistoryInfoMapEntry>::const_iterator iter =
-       entries.begin(); iter != entries.end(); ++iter) {
-    HistoryID history_id = iter->history_id();
-    GURL url(iter->url());
-    history::URLRow url_row(url, history_id);
-    url_row.set_visit_count(iter->visit_count());
-    url_row.set_typed_count(iter->typed_count());
-    url_row.set_last_visit(base::Time::FromInternalValue(iter->last_visit()));
-    if (iter->has_title()) {
-      base::string16 title(base::UTF8ToUTF16(iter->title()));
-      url_row.set_title(title);
-    }
-    history_info_map_[history_id].url_row = url_row;
+
+  for (const auto& entry : list_item.history_info_map_entry()) {
+    HistoryID history_id = entry.history_id();
+    history::URLRow url_row(GURL(entry.url()), history_id);
+    url_row.set_visit_count(entry.visit_count());
+    url_row.set_typed_count(entry.typed_count());
+    url_row.set_last_visit(base::Time::FromInternalValue(entry.last_visit()));
+    if (entry.has_title())
+      url_row.set_title(base::UTF8ToUTF16(entry.title()));
+    history_info_map_[history_id].url_row = std::move(url_row);
 
     // Restore visits list.
     VisitInfoVector visits;
-    visits.reserve(iter->visits_size());
-    for (int i = 0; i < iter->visits_size(); ++i) {
-      visits.push_back(std::make_pair(
-          base::Time::FromInternalValue(iter->visits(i).visit_time()),
-          ui::PageTransitionFromInt(iter->visits(i).transition_type())));
+    visits.reserve(entry.visits_size());
+    for (const auto& entry_visit : entry.visits()) {
+      visits.emplace_back(
+          base::Time::FromInternalValue(entry_visit.visit_time()),
+          ui::PageTransitionFromInt(entry_visit.transition_type()));
     }
-    history_info_map_[history_id].visits = visits;
+    history_info_map_[history_id].visits = std::move(visits);
   }
   return true;
 }
 
 bool URLIndexPrivateData::RestoreWordStartsMap(
     const InMemoryURLIndexCacheItem& cache) {
   // Note that this function must be called after RestoreHistoryInfoMap() has
   // been run as the word starts may have to be recalculated from the urls and
   // page titles.
   if (cache.has_word_starts_map()) {
     const WordStartsMapItem& list_item(cache.word_starts_map());
     uint32_t expected_item_count = list_item.item_count();
     uint32_t actual_item_count = list_item.word_starts_map_entry_size();
     if (actual_item_count == 0 || actual_item_count != expected_item_count)
       return false;
-    const RepeatedPtrField<WordStartsMapEntry>&
-        entries(list_item.word_starts_map_entry());
-    for (RepeatedPtrField<WordStartsMapEntry>::const_iterator iter =
-         entries.begin(); iter != entries.end(); ++iter) {
-      HistoryID history_id = iter->history_id();
+    for (const auto& entry : list_item.word_starts_map_entry()) {
+      HistoryID history_id = entry.history_id();
       RowWordStarts word_starts;
       // Restore the URL word starts.
-      const RepeatedField<int32_t>& url_starts(iter->url_word_starts());
-      for (RepeatedField<int32_t>::const_iterator jiter = url_starts.begin();
-           jiter != url_starts.end(); ++jiter)
-        word_starts.url_word_starts_.push_back(*jiter);
+      const RepeatedField<int32_t>& url_starts(entry.url_word_starts());
+      word_starts.url_word_starts_ = {url_starts.begin(), url_starts.end()};
+
       // Restore the page title word starts.
-      const RepeatedField<int32_t>& title_starts(iter->title_word_starts());
-      for (RepeatedField<int32_t>::const_iterator jiter = title_starts.begin();
-           jiter != title_starts.end(); ++jiter)
-        word_starts.title_word_starts_.push_back(*jiter);
-      word_starts_map_[history_id] = word_starts;
+      const RepeatedField<int32_t>& title_starts(entry.title_word_starts());
+      word_starts.title_word_starts_ = {title_starts.begin(),
+                                        title_starts.end()};
+
+      word_starts_map_[history_id] = std::move(word_starts);
     }
   } else {
     // Since the cache did not contain any word starts we must rebuild then from
     // the URL and page titles.
-    for (HistoryInfoMap::const_iterator iter = history_info_map_.begin();
-         iter != history_info_map_.end(); ++iter) {
+    for (const auto& entry : history_info_map_) {
       RowWordStarts word_starts;
-      const history::URLRow& row(iter->second.url_row);
+      const history::URLRow& row(entry.second.url_row);
       const base::string16& url =
           bookmarks::CleanUpUrlForMatching(row.url(), nullptr);
       String16VectorFromString16(url, false, &word_starts.url_word_starts_);
       const base::string16& title =
           bookmarks::CleanUpTitleForMatching(row.title());
       String16VectorFromString16(title, false, &word_starts.title_word_starts_);
-      word_starts_map_[iter->first] = word_starts;
+      word_starts_map_[entry.first] = std::move(word_starts);
     }
   }
   return true;
 }
 
 // static
 bool URLIndexPrivateData::URLSchemeIsWhitelisted(
     const GURL& gurl,
     const std::set<std::string>& whitelist) {
   return whitelist.find(gurl.scheme()) != whitelist.end();
@@ skipping 62 matching lines @@
   // First cut: typed count, visit count, recency.
   // TODO(mrossetti): This is too simplistic. Consider an approach which ranks
   // recently visited (within the last 12/24 hours) as highly important. Get
   // input from mpearson.
   if (r1.typed_count() != r2.typed_count())
     return (r1.typed_count() > r2.typed_count());
   if (r1.visit_count() != r2.visit_count())
     return (r1.visit_count() > r2.visit_count());
   return (r1.last_visit() > r2.last_visit());
 }