cros: Add HourAppLaunchPredictor for AppSearchResultRanker

(1) Add HourAppLaunchPredictor with unit test.

(2) Add SerializationTesterAppLaunchPredictor for testing
    AppSearchResultRanker materialization logic.

(3) Extend AppLaunchPredictor interface to support more functions.

Bug: 871674
Change-Id: I38bbc0b7efd1ed3576c4c3d170c553ec80dcec93
Reviewed-on: https://chromium-review.googlesource.com/1189506
Commit-Queue: Charles . <charleszhao@chromium.org>
Reviewed-by: Jia Meng <jiameng@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590133}

ash/public/cpp/app_list/app_list_features.cc

@@ -35,10 +35,8 @@ const base::Feature kEnableZeroStateSuggestions{
     "EnableZeroStateSuggestions", base::FEATURE_DISABLED_BY_DEFAULT};
 const base::Feature kEnableAppListSearchAutocomplete{
     "EnableAppListSearchAutocomplete", base::FEATURE_ENABLED_BY_DEFAULT};
-const base::Feature kEnableSearchResultRankerTrain{
-    "EnableSearchResultRankerTrain", base::FEATURE_DISABLED_BY_DEFAULT};
-const base::Feature kEnableSearchResultRankerInfer{
-    "EnableSearchResultRankerInfer", base::FEATURE_DISABLED_BY_DEFAULT};
+const base::Feature kEnableAppSearchResultRanker{
+    "EnableAppSearchResultRanker", base::FEATURE_DISABLED_BY_DEFAULT};
 
 bool IsAnswerCardEnabled() {
   // Not using local static variable to allow tests to change this value.
@@ -90,12 +88,8 @@ bool IsAppListSearchAutocompleteEnabled() {
   return base::FeatureList::IsEnabled(kEnableAppListSearchAutocomplete);
 }
 
-bool IsSearchResultRankerTrainEnabled() {
-  return base::FeatureList::IsEnabled(kEnableSearchResultRankerTrain);
-}
-
-bool IsSearchResultRankerInferEnabled() {
-  return base::FeatureList::IsEnabled(kEnableSearchResultRankerInfer);
+bool IsAppSearchResultRankerEnabled() {
+  return base::FeatureList::IsEnabled(kEnableAppSearchResultRanker);
 }
 
 std::string AnswerServerUrl() {
@@ -111,10 +105,9 @@ std::string AnswerServerQuerySuffix() {
                                                 "QuerySuffix");
 }
 
-std::string SearchResultRankerPredictorName() {
+std::string AppSearchResultRankerPredictorName() {
   const std::string predictor_name = base::GetFieldTrialParamValueByFeature(
-      kEnableSearchResultRankerTrain,
-      "app_search_result_ranker_predictor_name");
+      kEnableAppSearchResultRanker, "app_search_result_ranker_predictor_name");
   if (!predictor_name.empty())
     return predictor_name;
   return std::string("MrfuAppLaunchPredictor");

ash/public/cpp/app_list/app_list_features.h

@@ -61,13 +61,8 @@ ASH_PUBLIC_EXPORT extern const base::Feature kEnableZeroStateSuggestions;
 // Enables the feature to autocomplete text typed in the AppList search box.
 ASH_PUBLIC_EXPORT extern const base::Feature kEnableAppListSearchAutocomplete;
 
-// Enables the feature to rank app search result using AppSearchResultRanker
-// (only training).
-ASH_PUBLIC_EXPORT extern const base::Feature kEnableSearchResultRankerTrain;
-
-// Enables the feature to rank app search result using AppSearchResultRanker
-// (only inferencing).
-ASH_PUBLIC_EXPORT extern const base::Feature kEnableSearchResultRankerInfer;
+// Enables the feature to rank app search result using AppSearchResultRanker.
+ASH_PUBLIC_EXPORT extern const base::Feature kEnableAppSearchResultRanker;
 
 bool ASH_PUBLIC_EXPORT IsAnswerCardEnabled();
 bool ASH_PUBLIC_EXPORT IsAppShortcutSearchEnabled();
@@ -81,12 +76,11 @@ bool ASH_PUBLIC_EXPORT IsNewStyleLauncherEnabled();
 bool ASH_PUBLIC_EXPORT IsContinueReadingEnabled();
 bool ASH_PUBLIC_EXPORT IsZeroStateSuggestionsEnabled();
 bool ASH_PUBLIC_EXPORT IsAppListSearchAutocompleteEnabled();
-bool ASH_PUBLIC_EXPORT IsSearchResultRankerTrainEnabled();
-bool ASH_PUBLIC_EXPORT IsSearchResultRankerInferEnabled();
+bool ASH_PUBLIC_EXPORT IsAppSearchResultRankerEnabled();
 
 std::string ASH_PUBLIC_EXPORT AnswerServerUrl();
 std::string ASH_PUBLIC_EXPORT AnswerServerQuerySuffix();
-std::string ASH_PUBLIC_EXPORT SearchResultRankerPredictorName();
+std::string ASH_PUBLIC_EXPORT AppSearchResultRankerPredictorName();
 
 }  // namespace features
 }  // namespace app_list

chrome/browser/ui/BUILD.gn

@@ -3589,6 +3589,7 @@ jumbo_split_static_library("ui") {
       "//ash/app_list",
       "//ash/public/cpp/app_list/vector_icons",
       "//ash/resources/vector_icons",
+      "//chrome/browser/ui/app_list/search/search_result_ranker:app_launch_predictor_proto",
       "//ui/views/mus/remote_view:remote_view_provider",
     ]
 

chrome/browser/ui/app_list/search/app_search_provider.cc

@@ -31,6 +31,7 @@
 #include "chrome/browser/chromeos/crostini/crostini_registry_service_factory.h"
 #include "chrome/browser/chromeos/crostini/crostini_util.h"
 #include "chrome/browser/chromeos/extensions/gfx_utils.h"
+#include "chrome/browser/chromeos/profiles/profile_helper.h"
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/extensions/extension_ui_util.h"
 #include "chrome/browser/extensions/extension_util.h"
@@ -512,7 +513,9 @@ AppSearchProvider::AppSearchProvider(Profile* profile,
       list_controller_(list_controller),
       model_updater_(model_updater),
       clock_(clock),
-      ranker_(std::make_unique<AppSearchResultRanker>(profile)),
+      ranker_(std::make_unique<AppSearchResultRanker>(
+          profile->GetPath(),
+          chromeos::ProfileHelper::IsEphemeralUserProfile(profile))),
       update_results_factory_(this) {
   data_sources_.emplace_back(
       std::make_unique<ExtensionDataSource>(profile, this));

chrome/browser/ui/app_list/search/search_result_ranker/BUILD.gn

+# Copyright 2018 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.
+
+import("//third_party/protobuf/proto_library.gni")
+
+proto_library("app_launch_predictor_proto") {
+  sources = [
+    "app_launch_predictor.proto",
+  ]
+}

chrome/browser/ui/app_list/search/search_result_ranker/app_launch_predictor.cc

@@ -7,22 +7,37 @@
 #include <cmath>
 
 #include "base/logging.h"
+#include "base/stl_util.h"
 
 namespace app_list {
+namespace {
+
+constexpr int kHoursADay = 24;
+constexpr base::TimeDelta kSaveInternal = base::TimeDelta::FromHours(1);
+
+// A bin with index i has 5 adjacent bins as: i + 0, i + 1, i + 2, i + 22, and
+// i + 23. They each contributes to the final Rank score with different level:
+// 0.6 for i-th bin itself, 0.15 for i + 1 (one hour later) and i + 23 (
+// one hour earlier), 0.05 for i + 2 (two hours later) and i + 22 (two hours
+// earlier).
+constexpr int kAdjacentHourBin[] = {0, 1, 2, 22, 23};
+constexpr float kAdjacentHourWeight[] = {0.6, 0.15, 0.05, 0.05, 0.15};
+
+}  // namespace
 
 MrfuAppLaunchPredictor::MrfuAppLaunchPredictor() = default;
 MrfuAppLaunchPredictor::~MrfuAppLaunchPredictor() = default;
 
-// Updates the score for this |app_id|.
 void MrfuAppLaunchPredictor::Train(const std::string& app_id) {
+  // Updates the score for this |app_id|.
   ++num_of_trains_;
   Score& score = scores_[app_id];
   UpdateScore(&score);
   score.last_score += 1.0f - decay_coeff_;
 }
 
-// Updates all scores and return app_id to score map.
 base::flat_map<std::string, float> MrfuAppLaunchPredictor::Rank() {
+  // Updates all scores and return app_id to score map.
   base::flat_map<std::string, float> output;
   for (auto& pair : scores_) {
     UpdateScore(&pair.second);
@@ -31,8 +46,30 @@ base::flat_map<std::string, float> MrfuAppLaunchPredictor::Rank() {
   return output;
 }
 
-// Updates last_score and last_update_timestamp.
+const char MrfuAppLaunchPredictor::kPredictorName[] = "MrfuAppLaunchPredictor";
+const char* MrfuAppLaunchPredictor::GetPredictorName() const {
+  return kPredictorName;
+}
+
+bool MrfuAppLaunchPredictor::ShouldSave() {
+  // MrfuAppLaunchPredictor doesn't need materialization.
+  return false;
+}
+
+AppLaunchPredictorProto MrfuAppLaunchPredictor::ToProto() const {
+  // MrfuAppLaunchPredictor doesn't need materialization.
+  NOTREACHED();
+  return AppLaunchPredictorProto();
+}
+
+bool MrfuAppLaunchPredictor::FromProto(const AppLaunchPredictorProto& proto) {
+  // MrfuAppLaunchPredictor doesn't need materialization.
+  NOTREACHED();
+  return false;
+}
+
 void MrfuAppLaunchPredictor::UpdateScore(Score* score) {
+  // Updates last_score and num_of_trains_at_last_update.
   const int trains_since_last_time =
       num_of_trains_ - score->num_of_trains_at_last_update;
   if (trains_since_last_time > 0) {
@@ -41,4 +78,131 @@ void MrfuAppLaunchPredictor::UpdateScore(Score* score) {
   }
 }
 
+HourAppLaunchPredictor::HourAppLaunchPredictor()
+    : last_save_timestamp_(base::Time::Now()) {}
+
+HourAppLaunchPredictor::~HourAppLaunchPredictor() = default;
+
+void HourAppLaunchPredictor::Train(const std::string& app_id) {
+  auto& frequency_table = (*proto_.mutable_hour_app_launch_predictor()
+                                ->mutable_binned_frequency_table())[GetBin()];
+
+  frequency_table.set_total_counts(frequency_table.total_counts() + 1);
+  (*frequency_table.mutable_frequency())[app_id] += 1;
+}
+
+base::flat_map<std::string, float> HourAppLaunchPredictor::Rank() {
+  base::flat_map<std::string, float> output;
+  const int bin = GetBin();
+  const bool is_weekend = bin >= kHoursADay;
+  const int hour = bin % kHoursADay;
+  const auto& frequency_table_map =
+      proto_.hour_app_launch_predictor().binned_frequency_table();
+
+  for (size_t i = 0; i < base::size(kAdjacentHourBin); ++i) {
+    // Finds adjacent bin and weight.
+    const int adj_bin =
+        (hour + kAdjacentHourBin[i]) % kHoursADay + kHoursADay * is_weekend;
+    const auto find_frequency_table = frequency_table_map.find(adj_bin);
+    if (find_frequency_table == frequency_table_map.end())
+      continue;
+
+    const auto& frequency_table = find_frequency_table->second;
+    const float weight = kAdjacentHourWeight[i];
+
+    // Accumulates the frequency to the output.
+    if (frequency_table.total_counts() > 0) {
+      const int total_counts = frequency_table.total_counts();
+      for (const auto& pair : frequency_table.frequency()) {
+        output[pair.first] +=
+            static_cast<float>(pair.second) / total_counts * weight;
+      }
+    }
+  }
+  return output;
+}
+
+const char HourAppLaunchPredictor::kPredictorName[] = "HourAppLaunchPredictor";
+const char* HourAppLaunchPredictor::GetPredictorName() const {
+  return kPredictorName;
+}
+
+bool HourAppLaunchPredictor::ShouldSave() {
+  const base::Time now = base::Time::Now();
+  if (now - last_save_timestamp_ >= kSaveInternal) {
+    last_save_timestamp_ = now;
+    return true;
+  }
+  return false;
+}
+
+AppLaunchPredictorProto HourAppLaunchPredictor::ToProto() const {
+  return proto_;
+}
+
+bool HourAppLaunchPredictor::FromProto(const AppLaunchPredictorProto& proto) {
+  if (proto.predictor_case() !=
+      AppLaunchPredictorProto::kHourAppLaunchPredictor) {
+    return false;
+  }
+  proto_ = proto;
+  return true;
+}
+
+int HourAppLaunchPredictor::GetBin() const {
+  base::Time::Exploded now;
+  base::Time::Now().LocalExplode(&now);
+
+  const bool is_weekend = now.day_of_week == 6 || now.day_of_week == 0;
+
+  // To distinguish workdays with weekends, we use now.hour for workdays, and
+  // now.hour + 24 for weekends.
+  if (!is_weekend) {
+    return now.hour;
+  } else {
+    return now.hour + kHoursADay;
+  }
+}
+
+void FakeAppLaunchPredictor::SetShouldSave(bool should_save) {
+  should_save_ = should_save;
+}
+
+void FakeAppLaunchPredictor::Train(const std::string& app_id) {
+  // Increases 1.0 for rank score of app_id.
+  (*proto_.mutable_fake_app_launch_predictor()
+        ->mutable_rank_result())[app_id] += 1.0f;
+}
+
+base::flat_map<std::string, float> FakeAppLaunchPredictor::Rank() {
+  // Outputs proto_.fake_app_launch_predictor().rank_result() as Rank result.
+  base::flat_map<std::string, float> output;
+  for (const auto& pair : proto_.fake_app_launch_predictor().rank_result()) {
+    output[pair.first] = pair.second;
+  }
+  return output;
+}
+
+const char FakeAppLaunchPredictor::kPredictorName[] = "FakeAppLaunchPredictor";
+const char* FakeAppLaunchPredictor::GetPredictorName() const {
+  return kPredictorName;
+}
+
+bool FakeAppLaunchPredictor::ShouldSave() {
+  return should_save_;
+}
+
+AppLaunchPredictorProto FakeAppLaunchPredictor::ToProto() const {
+  return proto_;
+}
+
+bool FakeAppLaunchPredictor::FromProto(const AppLaunchPredictorProto& proto) {
+  if (proto.predictor_case() !=
+      AppLaunchPredictorProto::kFakeAppLaunchPredictor) {
+    return false;
+  }
+  proto_ = proto;
+  return true;
+}
+
 }  // namespace app_list

chrome/browser/ui/app_list/search/search_result_ranker/app_launch_predictor.h

@@ -10,6 +10,8 @@
 #include "base/containers/flat_map.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
+#include "base/time/time.h"
+#include "chrome/browser/ui/app_list/search/search_result_ranker/app_launch_predictor.pb.h"
 
 namespace app_list {
 
@@ -26,6 +28,14 @@ class AppLaunchPredictor {
   //  (3) The returned scores should be in range [0.0, 1.0] for
   //      AppSearchProvider to handle.
   virtual base::flat_map<std::string, float> Rank() = 0;
+  // Returns the name of the predictor.
+  virtual const char* GetPredictorName() const = 0;
+  // Whether the model should be saved on disk at this moment.
+  virtual bool ShouldSave() = 0;
+  // Converts the predictor to AppLaunchPredictorProto.
+  virtual AppLaunchPredictorProto ToProto() const = 0;
+  // Initializes the predictor with |proto|.
+  virtual bool FromProto(const AppLaunchPredictorProto& proto) = 0;
 };
 
 // MrfuAppLaunchPredictor is a simple AppLaunchPredictor that balances MRU (most
@@ -39,10 +49,16 @@ class MrfuAppLaunchPredictor : public AppLaunchPredictor {
   // AppLaunchPredictor:
   void Train(const std::string& app_id) override;
   base::flat_map<std::string, float> Rank() override;
+  const char* GetPredictorName() const override;
+  bool ShouldSave() override;
+  AppLaunchPredictorProto ToProto() const override;
+  bool FromProto(const AppLaunchPredictorProto& proto) override;
+
+  // Name of the predictor;
+  static const char kPredictorName[];
 
  private:
   FRIEND_TEST_ALL_PREFIXES(AppLaunchPredictorTest, MrfuAppLaunchPredictor);
-  FRIEND_TEST_ALL_PREFIXES(AppSearchResultRankerTest, TrainAndInfer);
 
   // Records last updates of the Score for an app.
   struct Score {
@@ -68,6 +84,75 @@ class MrfuAppLaunchPredictor : public AppLaunchPredictor {
   DISALLOW_COPY_AND_ASSIGN(MrfuAppLaunchPredictor);
 };
 
+// HourAppLaunchPredictor is a AppLaunchPredictor that uses hour of the day as
+// bins, and uses app-launch frequency of in each bin as the Rank score.
+// For example, if it's 8:30 am right now, then only app-launches between 8am to
+// 9am in the last a few days are mainly considered.
+// NOTE 1: bins of nearby hours also contributes to the final score but less
+//         significient. For example if current time is 8am, then scores in 6am,
+//         7am, 9am, and 10am are also added to the final Rank score with
+//         smaller weights.
+// NOTE 2: workdays and weekends are put into different bins.
+class HourAppLaunchPredictor : public AppLaunchPredictor {
+ public:
+  HourAppLaunchPredictor();
+  ~HourAppLaunchPredictor() override;
+
+  // AppLaunchPredictor:
+  void Train(const std::string& app_id) override;
+  base::flat_map<std::string, float> Rank() override;
+  const char* GetPredictorName() const override;
+  bool ShouldSave() override;
+  AppLaunchPredictorProto ToProto() const override;
+  bool FromProto(const AppLaunchPredictorProto& proto) override;
+
+  // Name of the predictor;
+  static const char kPredictorName[];
+
+ private:
+  FRIEND_TEST_ALL_PREFIXES(HourAppLaunchPredictorTest, GetTheRightBin);
+  FRIEND_TEST_ALL_PREFIXES(HourAppLaunchPredictorTest, RankFromSingleBin);
+  FRIEND_TEST_ALL_PREFIXES(HourAppLaunchPredictorTest, RankFromMultipleBin);
+
+  // Returns current bin index of this predictor.
+  int GetBin() const;
+
+  // The proto for this predictor.
+  AppLaunchPredictorProto proto_;
+  // Last time the predictor was saved.
+  base::Time last_save_timestamp_;
+
+  DISALLOW_COPY_AND_ASSIGN(HourAppLaunchPredictor);
+};
+
+// Predictor for testing AppSearchResultRanker only.
+class FakeAppLaunchPredictor : public AppLaunchPredictor {
+ public:
+  FakeAppLaunchPredictor() = default;
+  ~FakeAppLaunchPredictor() override = default;
+
+  // Manually set |should_save_|;
+  void SetShouldSave(bool should_save);
+
+  // AppLaunchPredictor:
+  void Train(const std::string& app_id) override;
+  base::flat_map<std::string, float> Rank() override;
+  const char* GetPredictorName() const override;
+  bool ShouldSave() override;
+  AppLaunchPredictorProto ToProto() const override;
+  bool FromProto(const AppLaunchPredictorProto& proto) override;
+
+  // Name of the predictor;
+  static const char kPredictorName[];
+
+ private:
+  bool should_save_ = false;
+  // The proto for this predictor.
+  AppLaunchPredictorProto proto_;
+
+  DISALLOW_COPY_AND_ASSIGN(FakeAppLaunchPredictor);
+};
+
 }  // namespace app_list
 
 #endif  // CHROME_BROWSER_UI_APP_LIST_SEARCH_SEARCH_RESULT_RANKER_APP_LAUNCH_PREDICTOR_H_

chrome/browser/ui/app_list/search/search_result_ranker/app_launch_predictor.proto

+// Copyright 2018 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.
+
+syntax = "proto2";
+
+option optimize_for = LITE_RUNTIME;
+
+package app_list;
+
+// HourAppLaunchPredictorProto is used for materializing HourAppLaunchPredictor.
+message HourAppLaunchPredictorProto {
+  // A frequency table records app launches that happened in a particular bin.
+  message FrequencyTable {
+    // Total number of launches (within this bin), should equal to the sum of
+    // frequency below.
+    optional int32 total_counts = 1;
+    // Number of launches for each app (within this bin).
+    map<string, int32> frequency = 2;
+  }
+  // A map from bin indices to each FrequencyTable of that bin.
+  map<int32, FrequencyTable> binned_frequency_table = 1;
+}
+
+// Used only for testing AppSearchResultRanker.
+message FakeAppLaunchPredictorProto {
+  map<string, float> rank_result = 1;
+}
+
+// AppLaunchPredictorProto contains one type of the predictor proto above.
+message AppLaunchPredictorProto {
+  oneof predictor {
+    FakeAppLaunchPredictorProto fake_app_launch_predictor = 1;
+    HourAppLaunchPredictorProto hour_app_launch_predictor = 2;
+  }
+}

chrome/browser/ui/app_list/search/search_result_ranker/app_launch_predictor_unittest.cc

@@ -4,6 +4,7 @@
 
 #include "chrome/browser/ui/app_list/search/search_result_ranker/app_launch_predictor.h"
 
+#include "base/test/scoped_mock_clock_override.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -41,4 +42,135 @@ TEST(AppLaunchPredictorTest, MrfuAppLaunchPredictor) {
                                    Pair(kTarget2, FloatEq(score_1))));
 }
 
+class HourAppLaunchPredictorTest : public testing::Test {
+ protected:
+  // Sets local time according to |day_of_week| and |hour_of_day|.
+  void SetLocalTime(const int day_of_week, const int hour_of_day) {
+    AdvanceToNextLocalSunday();
+    const auto advance = base::TimeDelta::FromDays(day_of_week) +
+                         base::TimeDelta::FromHours(hour_of_day);
+    if (advance > base::TimeDelta()) {
+      time_.Advance(advance);
+    }
+  }
+
+ private:
+  // Advances time to be 0am next Sunday.
+  void AdvanceToNextLocalSunday() {
+    base::Time::Exploded now;
+    base::Time::Now().LocalExplode(&now);
+    const auto advance = base::TimeDelta::FromDays(6 - now.day_of_week) +
+                         base::TimeDelta::FromHours(24 - now.hour);
+    if (advance > base::TimeDelta()) {
+      time_.Advance(advance);
+    }
+    base::Time::Now().LocalExplode(&now);
+    CHECK_EQ(now.day_of_week, 0);
+    CHECK_EQ(now.hour, 0);
+  }
+
+  base::ScopedMockClockOverride time_;
+};
+
+// Checks HourAppLaunchPredictor::GetBin returns the right bin index for given
+// local time.
+TEST_F(HourAppLaunchPredictorTest, GetTheRightBin) {
+  HourAppLaunchPredictor predictor;
+
+  // Monday.
+  for (int i = 0; i <= 23; ++i) {
+    SetLocalTime(1, i);
+    EXPECT_EQ(predictor.GetBin(), i);
+  }
+
+  // Friday.
+  for (int i = 0; i <= 23; ++i) {
+    SetLocalTime(5, i);
+    EXPECT_EQ(predictor.GetBin(), i);
+  }
+
+  // Saturday.
+  for (int i = 0; i <= 23; ++i) {
+    SetLocalTime(6, i);
+    EXPECT_EQ(predictor.GetBin(), i + 24);
+  }
+
+  // Sunday.
+  for (int i = 0; i <= 23; ++i) {
+    SetLocalTime(0, i);
+    EXPECT_EQ(predictor.GetBin(), i + 24);
+  }
+}
+
+// Checks the apps are ranked based on frequency in a single bin.
+TEST_F(HourAppLaunchPredictorTest, RankFromSingleBin) {
+  HourAppLaunchPredictor predictor;
+
+  // Create a model that trained on kTarget1 3 times, and kTarget2 2 times.
+  SetLocalTime(1, 10);
+  predictor.Train(kTarget1);
+  SetLocalTime(2, 10);
+  predictor.Train(kTarget1);
+  SetLocalTime(3, 10);
+  predictor.Train(kTarget1);
+  SetLocalTime(4, 10);
+  predictor.Train(kTarget2);
+  SetLocalTime(5, 10);
+  predictor.Train(kTarget2);
+
+  // Train on weekend will not fail into the same bin.
+  SetLocalTime(6, 10);
+  predictor.Train(kTarget1);
+  SetLocalTime(0, 10);
+  predictor.Train(kTarget2);
+
+  SetLocalTime(1, 10);
+  EXPECT_THAT(predictor.Rank(),
+              UnorderedElementsAre(Pair(kTarget1, FloatEq(0.6 * 0.6)),
+                                   Pair(kTarget2, FloatEq(0.6 * 0.4))));
+}
+
+// Checks the apps are ranked based on linearly combined scores from adjacent
+// bins.
+TEST_F(HourAppLaunchPredictorTest, RankFromMultipleBin) {
+  HourAppLaunchPredictor predictor;
+  // For bin 10
+  SetLocalTime(1, 10);
+  predictor.Train(kTarget1);
+  predictor.Train(kTarget1);
+  SetLocalTime(2, 10);
+  predictor.Train(kTarget2);
+
+  // For bin 11
+  SetLocalTime(3, 11);
+  predictor.Train(kTarget1);
+  predictor.Train(kTarget2);
+
+  // FOr bin 12
+  SetLocalTime(5, 12);
+  predictor.Train(kTarget2);
+
+  // Train on weekend.
+  SetLocalTime(6, 10);
+  predictor.Train(kTarget1);
+  predictor.Train(kTarget2);
+  SetLocalTime(0, 11);
+  predictor.Train(kTarget2);
+
+  // Check workdays.
+  SetLocalTime(1, 10);
+  EXPECT_THAT(
+      predictor.Rank(),
+      UnorderedElementsAre(
+          Pair(kTarget1, FloatEq(0.6 * 2.0 / 3.0 + 0.15 * 0.5)),
+          Pair(kTarget2, FloatEq(0.6 * 1.0 / 3.0 + 0.15 * 0.5 + 0.05 * 1.0))));
+
+  // Check weekends.
+  SetLocalTime(0, 9);
+  EXPECT_THAT(
+      predictor.Rank(),
+      UnorderedElementsAre(Pair(kTarget1, FloatEq(0.15 * 1.0 / 2.0)),
+                           Pair(kTarget2, FloatEq(0.15 * 1.0 / 2.0 + 0.05))));
+}
+
 }  // namespace app_list

chrome/browser/ui/app_list/search/search_result_ranker/app_search_result_ranker.cc

@@ -5,38 +5,141 @@
 #include "chrome/browser/ui/app_list/search/search_result_ranker/app_search_result_ranker.h"
 
 #include "ash/public/cpp/app_list/app_list_features.h"
+#include "base/files/file_util.h"
+#include "base/files/important_file_writer.h"
+#include "base/task/post_task.h"
+#include "base/task/task_traits.h"
+#include "base/task_runner_util.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/app_list/search/search_result_ranker/app_launch_predictor.h"
+#include "chrome/browser/ui/app_list/search/search_result_ranker/app_launch_predictor.pb.h"
 
 namespace app_list {
+namespace {
 
-AppSearchResultRanker::AppSearchResultRanker(Profile* profile) {
-  if (!features::IsSearchResultRankerTrainEnabled())
-    return;
+constexpr char kAppLaunchPredictorFilename[] = "app_launch_predictor";
+
+// Returns a AppLaunchPredictor pointer based on the |predictor_name|.
+std::unique_ptr<AppLaunchPredictor> CreatePredictor(
+    const std::string& predictor_name) {
+  if (predictor_name == MrfuAppLaunchPredictor::kPredictorName)
+    return std::make_unique<MrfuAppLaunchPredictor>();
+
+  if (predictor_name == HourAppLaunchPredictor::kPredictorName)
+    return std::make_unique<HourAppLaunchPredictor>();
+
+  if (predictor_name == FakeAppLaunchPredictor::kPredictorName)
+    return std::make_unique<FakeAppLaunchPredictor>();
 
-  if (features::SearchResultRankerPredictorName() == "MrfuAppLaunchPredictor") {
-    predictor_ = std::make_unique<MrfuAppLaunchPredictor>();
-    load_from_disk_success_ = true;
-  } else {
   NOTREACHED();
+  return nullptr;
+}
+
+// Save |proto| to |predictor_filename|.
+void SaveToDiskOnWorkerThread(const base::FilePath& predictor_filename,
+                              const AppLaunchPredictorProto& proto) {
+  base::AssertBlockingAllowed();
+
+  std::string proto_str;
+  if (!proto.SerializeToString(&proto_str))
+    return;
+
+  base::ImportantFileWriter::WriteFileAtomically(predictor_filename, proto_str,
+                                                 "AppSearchResultRanker");
+}
+
+// Loads a AppLaunchPredictor from |predictor_filename|.
+std::unique_ptr<AppLaunchPredictor> LoadPredictorFromDiskOnWorkerThread(
+    const base::FilePath& predictor_filename,
+    const std::string predictor_name) {
+  base::AssertBlockingAllowed();
+
+  // Loads proto string from local disk.
+  std::string proto_str;
+  if (!base::ReadFileToString(predictor_filename, &proto_str))
+    return nullptr;
+
+  // Parses proto string as AppLaunchPredictorProto.
+  AppLaunchPredictorProto proto;
+  if (!proto.ParseFromString(proto_str))
+    return nullptr;
+
+  auto predictor = CreatePredictor(predictor_name);
+  // Initializes the |predictor_| from the |proto|.
+  if (!predictor->FromProto(proto))
+    return nullptr;
+
+  return predictor;
+}
+
+}  // namespace
+
+AppSearchResultRanker::AppSearchResultRanker(const base::FilePath& profile_path,
+                                             bool is_ephemeral_user)
+    : predictor_filename_(
+          profile_path.AppendASCII(kAppLaunchPredictorFilename)),
+      weak_factory_(this) {
+  if (!features::IsAppSearchResultRankerEnabled())
+    return;
+
+  predictor_ = CreatePredictor(features::AppSearchResultRankerPredictorName());
+
+  // MrfuAppLaunchPredictor doesn't have materialization, so no loading from
+  // local disk.
+  if (predictor_->GetPredictorName() ==
+      MrfuAppLaunchPredictor::kPredictorName) {
+    load_from_disk_completed_ = true;
+    return;
   }
+
+  // For ephemeral users, we disable AppSearchResultRanker to make finch
+  // experiment easier.
+  if (is_ephemeral_user)
+    return;
+
+  task_runner_ = base::CreateSequencedTaskRunnerWithTraits(
+      {base::TaskPriority::BEST_EFFORT, base::MayBlock(),
+       base::TaskShutdownBehavior::SKIP_ON_SHUTDOWN});
+
+  // Loads the predictor from disk asynchronously.
+  base::PostTaskAndReplyWithResult(
+      task_runner_.get(), FROM_HERE,
+      base::BindOnce(&LoadPredictorFromDiskOnWorkerThread, predictor_filename_,
+                     predictor_->GetPredictorName()),
+      base::BindOnce(&AppSearchResultRanker::OnLoadFromDiskComplete,
+                     weak_factory_.GetWeakPtr()));
 }
 
 AppSearchResultRanker::~AppSearchResultRanker() = default;
 
 void AppSearchResultRanker::Train(const std::string& app_id) {
-  if (load_from_disk_success_ && predictor_) {
+  if (load_from_disk_completed_) {
     predictor_->Train(app_id);
+
+    if (predictor_->ShouldSave()) {
+      // Writes the predictor proto to disk asynchronously.
+      task_runner_->PostTask(
+          FROM_HERE,
+          base::BindOnce(&SaveToDiskOnWorkerThread, predictor_filename_,
+                         predictor_->ToProto()));
+    }
   }
 }
 
 base::flat_map<std::string, float> AppSearchResultRanker::Rank() {
-  if (load_from_disk_success_ && features::IsSearchResultRankerInferEnabled() &&
-      predictor_) {
+  if (load_from_disk_completed_) {
     return predictor_->Rank();
   }
 
   return {};
 }
 
+void AppSearchResultRanker::OnLoadFromDiskComplete(
+    std::unique_ptr<AppLaunchPredictor> predictor) {
+  if (predictor) {
+    predictor_.swap(predictor);
+  }
+  load_from_disk_completed_ = true;
+}
+
 }  // namespace app_list

chrome/browser/ui/app_list/search/search_result_ranker/app_search_result_ranker.h

@@ -9,9 +9,11 @@
 #include <string>
 
 #include "base/containers/flat_map.h"
+#include "base/files/file_path.h"
 #include "base/macros.h"
-
-class Profile;
+#include "base/memory/scoped_refptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/sequenced_task_runner.h"
 
 namespace app_list {
 
@@ -22,11 +24,15 @@ class AppLaunchPredictor;
 class AppSearchResultRanker {
  public:
   // Construct a AppSearchResultRanker with profile. It (possibly)
-  // asynchronously loads model from disk from profile->GetPath(); and sets
+  // asynchronously loads model from disk from |profile_path|; and sets
   // |load_from_disk_success_| to true when the loading finishes.
   // The internal |predictor_| is constructed with param
   // SearchResultRankerPredictorName() in "app_list_features.h".
-  explicit AppSearchResultRanker(Profile* profile);
+  // Ephemeral users are speically handled since their profiles are cleaned up
+  // after logging out.
+  explicit AppSearchResultRanker(const base::FilePath& profile_path,
+                                 bool is_ephemeral_user);
+
   ~AppSearchResultRanker();
 
   // Trains on the |app_id| and (possibly) updates its internal representation.
@@ -39,9 +45,25 @@ class AppSearchResultRanker {
   base::flat_map<std::string, float> Rank();
 
  private:
+  FRIEND_TEST_ALL_PREFIXES(AppSearchResultRankerSerializationTest,
+                           LoadFromDiskSucceed);
+  FRIEND_TEST_ALL_PREFIXES(AppSearchResultRankerSerializationTest,
+                           LoadFromDiskFailIfNoFileExists);
+  FRIEND_TEST_ALL_PREFIXES(AppSearchResultRankerSerializationTest,
+                           LoadFromDiskFailWithInvalidProto);
+  FRIEND_TEST_ALL_PREFIXES(AppSearchResultRankerSerializationTest,
+                           SaveToDiskSucceed);
+
+  // Sets |predictor_| and |load_from_disk_completed_| when
+  // LoadPredictorFromDiskOnWorkerThread completes.
+  void OnLoadFromDiskComplete(std::unique_ptr<AppLaunchPredictor> predictor);
+
   // Internal predictor used for train and rank.
   std::unique_ptr<AppLaunchPredictor> predictor_;
-  bool load_from_disk_success_ = false;
+  bool load_from_disk_completed_ = false;
+  const base::FilePath predictor_filename_;
+  scoped_refptr<base::SequencedTaskRunner> task_runner_;
+  base::WeakPtrFactory<AppSearchResultRanker> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(AppSearchResultRanker);
 };

chrome/browser/ui/app_list/search/search_result_ranker/app_search_result_ranker_unittest.cc

@@ -5,8 +5,11 @@
 #include "chrome/browser/ui/app_list/search/search_result_ranker/app_search_result_ranker.h"
 
 #include "ash/public/cpp/app_list/app_list_features.h"
+#include "base/files/scoped_temp_dir.h"
 #include "base/test/scoped_feature_list.h"
+#include "base/test/scoped_task_environment.h"
 #include "chrome/browser/ui/app_list/search/search_result_ranker/app_launch_predictor.h"
+#include "chrome/browser/ui/app_list/search/search_result_ranker/app_launch_predictor.pb.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -20,52 +23,187 @@ namespace {
 
 constexpr char kTarget1[] = "Target1";
 constexpr char kTarget2[] = "Target2";
+constexpr bool kNotAnEphemeralUser = false;
 
 }  // namespace
 
-TEST(AppSearchResultRankerTest, TrainAndInfer) {
+// Test flags of AppSearchResultRanker.
+class AppSearchResultRankerFlagTest : public testing::Test {
+ protected:
+  void SetUp() override {
+    Test::SetUp();
+    // Creates file directory.
+    ASSERT_TRUE(temp_dir_.CreateUniqueTempDir());
+  }
+
+  // Waits for all tasks in to finish.
+  void Wait() { scoped_task_environment_.RunUntilIdle(); }
+
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
+  base::ScopedTempDir temp_dir_;
   base::test::ScopedFeatureList scoped_feature_list_;
-  scoped_feature_list_.InitWithFeatures(
-      {features::kEnableSearchResultRankerTrain,
-       features::kEnableSearchResultRankerInfer},
-      {});
+};
 
-  AppSearchResultRanker ranker(nullptr);
+TEST_F(AppSearchResultRankerFlagTest, TrainAndInfer) {
+  scoped_feature_list_.InitAndEnableFeatureWithParameters(
+      features::kEnableAppSearchResultRanker,
+      {{"app_search_result_ranker_predictor_name",
+        FakeAppLaunchPredictor::kPredictorName}});
+
+  AppSearchResultRanker ranker(temp_dir_.GetPath(), kNotAnEphemeralUser);
+  Wait();
   ranker.Train(kTarget1);
   ranker.Train(kTarget2);
+  ranker.Train(kTarget2);
 
-  const float decay = MrfuAppLaunchPredictor::decay_coeff_;
-
-  EXPECT_THAT(
-      ranker.Rank(),
-      UnorderedElementsAre(Pair(kTarget1, FloatEq((1.0f - decay) * decay)),
-                           Pair(kTarget2, FloatEq(1.0f - decay))));
+  EXPECT_THAT(ranker.Rank(),
+              UnorderedElementsAre(Pair(kTarget1, FloatEq(1.0f)),
+                                   Pair(kTarget2, FloatEq(2.0f))));
 }
 
-TEST(AppSearchResultRankerTest, ReturnEmptyIfInferIsDisabled) {
-  base::test::ScopedFeatureList scoped_feature_list_;
-  scoped_feature_list_.InitWithFeatures(
-      {features::kEnableSearchResultRankerTrain},
-      {features::kEnableSearchResultRankerInfer});
+TEST_F(AppSearchResultRankerFlagTest, EphemeralUsersAreDisabled) {
+  scoped_feature_list_.InitAndEnableFeatureWithParameters(
+      features::kEnableAppSearchResultRanker,
+      {{"app_search_result_ranker_predictor_name",
+        FakeAppLaunchPredictor::kPredictorName}});
 
-  AppSearchResultRanker ranker(nullptr);
+  AppSearchResultRanker ranker(temp_dir_.GetPath(), !kNotAnEphemeralUser);
+  Wait();
   ranker.Train(kTarget1);
   ranker.Train(kTarget2);
+  ranker.Train(kTarget2);
 
   EXPECT_TRUE(ranker.Rank().empty());
 }
 
-TEST(AppSearchResultRankerTest, ReturnEmptyIfTrainIsDisabled) {
-  base::test::ScopedFeatureList scoped_feature_list_;
+TEST_F(AppSearchResultRankerFlagTest, ReturnEmptyIfDisabled) {
   scoped_feature_list_.InitWithFeatures(
-      {features::kEnableSearchResultRankerTrain},
-      {features::kEnableSearchResultRankerInfer});
+      {}, {features::kEnableAppSearchResultRanker});
 
-  AppSearchResultRanker ranker(nullptr);
+  AppSearchResultRanker ranker(temp_dir_.GetPath(), kNotAnEphemeralUser);
+  Wait();
   ranker.Train(kTarget1);
   ranker.Train(kTarget2);
 
   EXPECT_TRUE(ranker.Rank().empty());
 }
 
+// Test Serialization of AppSearchResultRanker.
+class AppSearchResultRankerSerializationTest
+    : public AppSearchResultRankerFlagTest {
+ protected:
+  void SetUp() override {
+    AppSearchResultRankerFlagTest::SetUp();
+
+    predictor_filename_ =
+        temp_dir_.GetPath().AppendASCII("app_launch_predictor");
+
+    // Sets proto.
+    AppLaunchPredictorProto proto;
+    (*proto.mutable_fake_app_launch_predictor()
+          ->mutable_rank_result())[kTarget1] = 1.0f;
+    (*proto.mutable_fake_app_launch_predictor()
+          ->mutable_rank_result())[kTarget2] = 2.0f;
+    ASSERT_TRUE(proto.SerializeToString(&proto_str_));
+
+    scoped_feature_list_.InitAndEnableFeatureWithParameters(
+        features::kEnableAppSearchResultRanker,
+        {{"app_search_result_ranker_predictor_name",
+          FakeAppLaunchPredictor::kPredictorName}});
+  }
+
+  base::FilePath predictor_filename_;
+  std::string proto_str_;
+};
+
+TEST_F(AppSearchResultRankerSerializationTest, LoadFromDiskSucceed) {
+  // Prepare file to be loaded.
+  EXPECT_NE(base::WriteFile(predictor_filename_, proto_str_.c_str(),
+                            proto_str_.size()),
+            -1);
+  // Construct ranker.
+  AppSearchResultRanker ranker(temp_dir_.GetPath(), kNotAnEphemeralUser);
+
+  // Check that the file loading is executed in non-blocking way.
+  EXPECT_FALSE(ranker.load_from_disk_completed_);
+
+  // Wait for the loading to finish.
+  Wait();
+
+  // Check loading is complete.
+  EXPECT_TRUE(ranker.load_from_disk_completed_);
+
+  // Check predictor is loaded correctly.
+  EXPECT_THAT(ranker.Rank(),
+              UnorderedElementsAre(Pair(kTarget1, FloatEq((1.0f))),
+                                   Pair(kTarget2, FloatEq(2.0f))));
+}
+
+TEST_F(AppSearchResultRankerSerializationTest, LoadFromDiskFailIfNoFileExists) {
+  // Construct ranker.
+  AppSearchResultRanker ranker(temp_dir_.GetPath(), kNotAnEphemeralUser);
+  // Wait for the loading to finish.
+  Wait();
+
+  // Check loading is complete.
+  EXPECT_TRUE(ranker.load_from_disk_completed_);
+
+  // Check predictor is initialized.
+  EXPECT_TRUE(ranker.Rank().empty());
+}
+
+TEST_F(AppSearchResultRankerSerializationTest,
+       LoadFromDiskFailWithInvalidProto) {
+  const std::string wrong_proto = "abc";
+  // Prepare file to be loaded.
+  EXPECT_NE(base::WriteFile(predictor_filename_, wrong_proto.c_str(),
+                            wrong_proto.size()),
+            -1);
+
+  // Construct ranker.
+  AppSearchResultRanker ranker(temp_dir_.GetPath(), kNotAnEphemeralUser);
+  // Wait for the loading to finish.
+  Wait();
+
+  // Check loading is complete.
+  EXPECT_TRUE(ranker.load_from_disk_completed_);
+
+  // Check predictor is initialized since the proto is not decodable.
+  EXPECT_TRUE(ranker.Rank().empty());
+}
+
+TEST_F(AppSearchResultRankerSerializationTest, SaveToDiskSucceed) {
+  // Construct ranker.
+  AppSearchResultRanker ranker(temp_dir_.GetPath(), kNotAnEphemeralUser);
+  // Wait for the loading to finish.
+  Wait();
+
+  // Check loading is complete.
+  EXPECT_TRUE(ranker.load_from_disk_completed_);
+  // Check predictor is initialized.
+  EXPECT_TRUE(ranker.Rank().empty());
+
+  ranker.Train(kTarget1);
+  ranker.Train(kTarget2);
+
+  // Check the predictor file is not created.
+  EXPECT_FALSE(base::PathExists(predictor_filename_));
+
+  // Set should_save to true.
+  static_cast<FakeAppLaunchPredictor*>(ranker.predictor_.get())
+      ->SetShouldSave(true);
+
+  // Train and wait for the writing to finish.
+  ranker.Train(kTarget2);
+  Wait();
+
+  // Expect the predictor file is created.
+  EXPECT_TRUE(base::PathExists(predictor_filename_));
+
+  // Expect the content to be proto_str_.
+  std::string str_written;
+  EXPECT_TRUE(base::ReadFileToString(predictor_filename_, &str_written));
+  EXPECT_EQ(str_written, proto_str_);
+}
+
 }  // namespace app_list

chrome/browser/ui/app_list/search/tests/app_search_provider_unittest.cc

@@ -336,9 +336,7 @@ TEST_F(AppSearchProviderTest, FetchUnlaunchedRecommendations) {
 TEST_F(AppSearchProviderTest, FetchRecommendationsFromRanker) {
   base::test::ScopedFeatureList scoped_feature_list_;
   scoped_feature_list_.InitWithFeatures(
-      {features::kEnableSearchResultRankerTrain,
-       features::kEnableSearchResultRankerInfer},
-      {});
+      {features::kEnableAppSearchResultRanker}, {});
   CreateSearch();
 
   extensions::ExtensionPrefs* prefs =
@@ -360,8 +358,7 @@ TEST_F(AppSearchProviderTest, FetchRecommendationsFromRanker) {
 TEST_F(AppSearchProviderTest, RankerIsDisabledWithFlag) {
   base::test::ScopedFeatureList scoped_feature_list_;
   scoped_feature_list_.InitWithFeatures(
-      {features::kEnableSearchResultRankerTrain},
-      {features::kEnableSearchResultRankerInfer});
+      {}, {features::kEnableAppSearchResultRanker});
   CreateSearch();
 
   extensions::ExtensionPrefs* prefs =