diff --git a/Android.mk b/Android.mk
index 01fb73e..915f103 100644
--- a/Android.mk
+++ b/Android.mk
@@ -321,6 +321,8 @@
 	core/java/android/service/wallpaper/IWallpaperService.aidl \
 	core/java/android/service/chooser/IChooserTargetService.aidl \
 	core/java/android/service/chooser/IChooserTargetResult.aidl \
+	core/java/android/service/resolver/IResolverRankerService.aidl \
+	core/java/android/service/resolver/IResolverRankerResult.aidl \
 	core/java/android/text/ITextClassificationService.aidl \
 	core/java/android/view/accessibility/IAccessibilityInteractionConnection.aidl\
 	core/java/android/view/accessibility/IAccessibilityInteractionConnectionCallback.aidl\
@@ -729,6 +731,7 @@
 	frameworks/base/core/java/android/service/notification/SnoozeCriterion.aidl \
 	frameworks/base/core/java/android/service/notification/StatusBarNotification.aidl \
 	frameworks/base/core/java/android/service/chooser/ChooserTarget.aidl \
+	frameworks/base/core/java/android/service/resolver/ResolverTarget.aidl \
 	frameworks/base/core/java/android/speech/tts/Voice.aidl \
 	frameworks/base/core/java/android/app/usage/CacheQuotaHint.aidl \
 	frameworks/base/core/java/android/app/usage/ExternalStorageStats.aidl \
diff --git a/api/system-current.txt b/api/system-current.txt
index 16e6f5b..ede909a 100644
--- a/api/system-current.txt
+++ b/api/system-current.txt
@@ -53,6 +53,7 @@
     field public static final java.lang.String BIND_PRINT_SERVICE = "android.permission.BIND_PRINT_SERVICE";
     field public static final java.lang.String BIND_QUICK_SETTINGS_TILE = "android.permission.BIND_QUICK_SETTINGS_TILE";
     field public static final java.lang.String BIND_REMOTEVIEWS = "android.permission.BIND_REMOTEVIEWS";
+    field public static final java.lang.String BIND_RESOLVER_RANKER_SERVICE = "android.permission.BIND_RESOLVER_RANKER_SERVICE";
     field public static final java.lang.String BIND_RUNTIME_PERMISSION_PRESENTER_SERVICE = "android.permission.BIND_RUNTIME_PERMISSION_PRESENTER_SERVICE";
     field public static final java.lang.String BIND_SCREENING_SERVICE = "android.permission.BIND_SCREENING_SERVICE";
     field public static final java.lang.String BIND_TELECOM_CONNECTION_SERVICE = "android.permission.BIND_TELECOM_CONNECTION_SERVICE";
@@ -40619,6 +40620,36 @@
 
 }
 
+package android.service.resolver {
+
+  public abstract class ResolverRankerService extends android.app.Service {
+    ctor public ResolverRankerService();
+    method public android.os.IBinder onBind(android.content.Intent);
+    method public void onPredictSharingProbabilities(java.util.List<android.service.resolver.ResolverTarget>);
+    method public void onTrainRankingModel(java.util.List<android.service.resolver.ResolverTarget>, int);
+    field public static final java.lang.String BIND_PERMISSION = "android.permission.BIND_RESOLVER_RANKER_SERVICE";
+    field public static final java.lang.String SERVICE_INTERFACE = "android.service.resolver.ResolverRankerService";
+  }
+
+  public final class ResolverTarget implements android.os.Parcelable {
+    ctor public ResolverTarget();
+    method public int describeContents();
+    method public float getChooserScore();
+    method public float getLaunchScore();
+    method public float getRecencyScore();
+    method public float getSelectProbability();
+    method public float getTimeSpentScore();
+    method public void setChooserScore(float);
+    method public void setLaunchScore(float);
+    method public void setRecencyScore(float);
+    method public void setSelectProbability(float);
+    method public void setTimeSpentScore(float);
+    method public void writeToParcel(android.os.Parcel, int);
+    field public static final android.os.Parcelable.Creator<android.service.resolver.ResolverTarget> CREATOR;
+  }
+
+}
+
 package android.service.restrictions {
 
   public abstract class RestrictionsReceiver extends android.content.BroadcastReceiver {
diff --git a/core/java/android/service/resolver/IResolverRankerResult.aidl b/core/java/android/service/resolver/IResolverRankerResult.aidl
new file mode 100644
index 0000000..bda3154
--- /dev/null
+++ b/core/java/android/service/resolver/IResolverRankerResult.aidl
@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.service.resolver;
+
+import android.service.resolver.ResolverTarget;
+
+/**
+ * @hide
+ */
+oneway interface IResolverRankerResult
+{
+    void sendResult(in List<ResolverTarget> results);
+}
\ No newline at end of file
diff --git a/core/java/android/service/resolver/IResolverRankerService.aidl b/core/java/android/service/resolver/IResolverRankerService.aidl
new file mode 100644
index 0000000..f0d747d
--- /dev/null
+++ b/core/java/android/service/resolver/IResolverRankerService.aidl
@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.service.resolver;
+
+import android.service.resolver.IResolverRankerResult;
+import android.service.resolver.ResolverTarget;
+
+/**
+ * @hide
+ */
+oneway interface IResolverRankerService
+{
+    void predict(in List<ResolverTarget> targets, IResolverRankerResult result);
+    void train(in List<ResolverTarget> targets, int selectedPosition);
+}
\ No newline at end of file
diff --git a/core/java/android/service/resolver/ResolverRankerService.java b/core/java/android/service/resolver/ResolverRankerService.java
new file mode 100644
index 0000000..0506747
--- /dev/null
+++ b/core/java/android/service/resolver/ResolverRankerService.java
@@ -0,0 +1,187 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.service.resolver;
+
+import android.annotation.SdkConstant;
+import android.annotation.SystemApi;
+import android.app.Service;
+import android.content.ComponentName;
+import android.content.Intent;
+import android.os.IBinder;
+import android.os.Handler;
+import android.os.HandlerThread;
+import android.os.RemoteException;
+import android.service.resolver.ResolverTarget;
+import android.util.Log;
+
+import java.util.List;
+import java.util.Map;
+
+/**
+ * A service to rank apps according to usage stats of apps, when the system is resolving targets for
+ * an Intent.
+ *
+ * <p>To extend this class, you must declare the service in your manifest file with the
+ * {@link android.Manifest.permission#BIND_RESOLVER_RANKER_SERVICE} permission, and include an
+ * intent filter with the {@link #SERVICE_INTERFACE} action. For example:</p>
+ * <pre>
+ *     &lt;service android:name=".MyResolverRankerService"
+ *             android:exported="true"
+ *             android:priority="100"
+ *             android:permission="android.permission.BIND_RESOLVER_RANKER_SERVICE"&gt;
+ *         &lt;intent-filter&gt;
+ *             &lt;action android:name="android.service.resolver.ResolverRankerService" /&gt;
+ *         &lt;/intent-filter&gt;
+ *     &lt;/service&gt;
+ * </pre>
+ * @hide
+ */
+@SystemApi
+public abstract class ResolverRankerService extends Service {
+
+    private static final String TAG = "ResolverRankerService";
+
+    private static final boolean DEBUG = false;
+
+    /**
+     * The Intent action that a service must respond to. Add it to the intent filter of the service
+     * in its manifest.
+     */
+    @SdkConstant(SdkConstant.SdkConstantType.SERVICE_ACTION)
+    public static final String SERVICE_INTERFACE = "android.service.resolver.ResolverRankerService";
+
+    /**
+     * The permission that a service must require to ensure that only Android system can bind to it.
+     * If this permission is not enforced in the AndroidManifest of the service, the system will
+     * skip that service.
+     */
+    public static final String BIND_PERMISSION = "android.permission.BIND_RESOLVER_RANKER_SERVICE";
+
+    private ResolverRankerServiceWrapper mWrapper = null;
+
+    /**
+     * Called by the system to retrieve a list of probabilities to rank apps/options. To implement
+     * it, set selectProbability of each input {@link ResolverTarget}. The higher the
+     * selectProbability is, the more likely the {@link ResolverTarget} will be selected by the
+     * user. Override this function to provide prediction results.
+     *
+     * @param targets a list of {@link ResolverTarget}, for the list of apps to be ranked.
+     *
+     * @throws Exception when the prediction task fails.
+     */
+    public void onPredictSharingProbabilities(final List<ResolverTarget> targets) {}
+
+    /**
+     * Called by the system to train/update a ranking service, after the user makes a selection from
+     * the ranked list of apps. Override this function to enable model updates.
+     *
+     * @param targets a list of {@link ResolverTarget}, for the list of apps to be ranked.
+     * @param selectedPosition the position of the selected app in the list.
+     *
+     * @throws Exception when the training task fails.
+     */
+    public void onTrainRankingModel(
+            final List<ResolverTarget> targets, final int selectedPosition) {}
+
+    private static final String HANDLER_THREAD_NAME = "RESOLVER_RANKER_SERVICE";
+    private volatile Handler mHandler;
+    private HandlerThread mHandlerThread;
+
+    @Override
+    public IBinder onBind(Intent intent) {
+        if (DEBUG) Log.d(TAG, "onBind " + intent);
+        if (!SERVICE_INTERFACE.equals(intent.getAction())) {
+            if (DEBUG) Log.d(TAG, "bad intent action " + intent.getAction() + "; returning null");
+            return null;
+        }
+        if (mHandlerThread == null) {
+            mHandlerThread = new HandlerThread(HANDLER_THREAD_NAME);
+            mHandlerThread.start();
+            mHandler = new Handler(mHandlerThread.getLooper());
+        }
+        if (mWrapper == null) {
+            mWrapper = new ResolverRankerServiceWrapper();
+        }
+        return mWrapper;
+    }
+
+    @Override
+    public void onDestroy() {
+        mHandler = null;
+        if (mHandlerThread != null) {
+            mHandlerThread.quitSafely();
+        }
+        super.onDestroy();
+    }
+
+    private static void sendResult(List<ResolverTarget> targets, IResolverRankerResult result) {
+        try {
+            result.sendResult(targets);
+        } catch (Exception e) {
+            Log.e(TAG, "failed to send results: " + e);
+        }
+    }
+
+    private class ResolverRankerServiceWrapper extends IResolverRankerService.Stub {
+
+        @Override
+        public void predict(final List<ResolverTarget> targets, final IResolverRankerResult result)
+                throws RemoteException {
+            Runnable predictRunnable = new Runnable() {
+                @Override
+                public void run() {
+                    try {
+                        if (DEBUG) {
+                            Log.d(TAG, "predict calls onPredictSharingProbabilities.");
+                        }
+                        onPredictSharingProbabilities(targets);
+                        sendResult(targets, result);
+                    } catch (Exception e) {
+                        Log.e(TAG, "onPredictSharingProbabilities failed; send null results: " + e);
+                        sendResult(null, result);
+                    }
+                }
+            };
+            final Handler h = mHandler;
+            if (h != null) {
+                h.post(predictRunnable);
+            }
+        }
+
+        @Override
+        public void train(final List<ResolverTarget> targets, final int selectedPosition)
+                throws RemoteException {
+            Runnable trainRunnable = new Runnable() {
+                @Override
+                public void run() {
+                    try {
+                        if (DEBUG) {
+                            Log.d(TAG, "train calls onTranRankingModel");
+                        }
+                        onTrainRankingModel(targets, selectedPosition);
+                    } catch (Exception e) {
+                        Log.e(TAG, "onTrainRankingModel failed; skip train: " + e);
+                    }
+                }
+            };
+            final Handler h = mHandler;
+            if (h != null) {
+                h.post(trainRunnable);
+            }
+        }
+    }
+}
diff --git a/core/java/android/service/resolver/ResolverTarget.aidl b/core/java/android/service/resolver/ResolverTarget.aidl
new file mode 100644
index 0000000..6cab2d4
--- /dev/null
+++ b/core/java/android/service/resolver/ResolverTarget.aidl
@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.service.resolver;
+
+/**
+ * @hide
+ */
+parcelable ResolverTarget;
diff --git a/core/java/android/service/resolver/ResolverTarget.java b/core/java/android/service/resolver/ResolverTarget.java
new file mode 100644
index 0000000..fb3e2d7
--- /dev/null
+++ b/core/java/android/service/resolver/ResolverTarget.java
@@ -0,0 +1,216 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.service.resolver;
+
+import android.annotation.SystemApi;
+import android.os.Bundle;
+import android.os.Parcel;
+import android.os.Parcelable;
+import android.util.ArrayMap;
+
+import java.util.Map;
+
+/**
+ * A ResolverTarget contains features by which an app or option will be ranked, in
+ * {@link ResolverRankerService}.
+ * @hide
+ */
+@SystemApi
+public final class ResolverTarget implements Parcelable {
+    private static final String TAG = "ResolverTarget";
+
+    /**
+     * a float score for recency of last use.
+     */
+    private float mRecencyScore;
+
+    /**
+     * a float score for total time spent.
+     */
+    private float mTimeSpentScore;
+
+    /**
+     * a float score for number of launches.
+     */
+    private float mLaunchScore;
+
+    /**
+     * a float score for number of selected.
+     */
+    private float mChooserScore;
+
+    /**
+     * a float score for the probability to be selected.
+     */
+    private float mSelectProbability;
+
+    // constructor for the class.
+    public ResolverTarget() {}
+
+    ResolverTarget(Parcel in) {
+        mRecencyScore = in.readFloat();
+        mTimeSpentScore = in.readFloat();
+        mLaunchScore = in.readFloat();
+        mChooserScore = in.readFloat();
+        mSelectProbability = in.readFloat();
+    }
+
+    /**
+     * Gets the score for how recently the target was used in the foreground.
+     *
+     * @return a float score whose range is [0, 1]. The higher the score is, the more recently the
+     * target was used.
+     */
+    public float getRecencyScore() {
+        return mRecencyScore;
+    }
+
+    /**
+     * Sets the score for how recently the target was used in the foreground.
+     *
+     * @param recencyScore a float score whose range is [0, 1]. The higher the score is, the more
+     *                     recently the target was used.
+     */
+    public void setRecencyScore(float recencyScore) {
+        this.mRecencyScore = recencyScore;
+    }
+
+    /**
+     * Gets the score for how long the target has been used in the foreground.
+     *
+     * @return a float score whose range is [0, 1]. The higher the score is, the longer the target
+     * has been used for.
+     */
+    public float getTimeSpentScore() {
+        return mTimeSpentScore;
+    }
+
+    /**
+     * Sets the score for how long the target has been used in the foreground.
+     *
+     * @param timeSpentScore a float score whose range is [0, 1]. The higher the score is, the
+     *                       longer the target has been used for.
+     */
+    public void setTimeSpentScore(float timeSpentScore) {
+        this.mTimeSpentScore = timeSpentScore;
+    }
+
+    /**
+     * Gets the score for how many times the target has been launched to the foreground.
+     *
+     * @return a float score whose range is [0, 1]. The higher the score is, the more times the
+     * target has been launched.
+     */
+    public float getLaunchScore() {
+        return mLaunchScore;
+    }
+
+    /**
+     * Sets the score for how many times the target has been launched to the foreground.
+     *
+     * @param launchScore a float score whose range is [0, 1]. The higher the score is, the more
+     *                    times the target has been launched.
+     */
+    public void setLaunchScore(float launchScore) {
+        this.mLaunchScore = launchScore;
+    }
+
+    /**
+     * Gets the score for how many times the target has been selected by the user to share the same
+     * types of content.
+     *
+     * @return a float score whose range is [0, 1]. The higher the score is, the
+     * more times the target has been selected by the user to share the same types of content for.
+     */
+    public float getChooserScore() {
+        return mChooserScore;
+    }
+
+    /**
+     * Sets the score for how many times the target has been selected by the user to share the same
+     * types of content.
+     *
+     * @param chooserScore a float score whose range is [0, 1]. The higher the score is, the more
+     *                     times the target has been selected by the user to share the same types
+     *                     of content for.
+     */
+    public void setChooserScore(float chooserScore) {
+        this.mChooserScore = chooserScore;
+    }
+
+    /**
+     * Gets the probability of how likely this target will be selected by the user.
+     *
+     * @return a float score whose range is [0, 1]. The higher the score is, the more likely the
+     * user is going to select this target.
+     */
+    public float getSelectProbability() {
+        return mSelectProbability;
+    }
+
+    /**
+     * Sets the probability for how like this target will be selected by the user.
+     *
+     * @param selectProbability a float score whose range is [0, 1]. The higher the score is, the
+     *                          more likely tht user is going to select this target.
+     */
+    public void setSelectProbability(float selectProbability) {
+        this.mSelectProbability = selectProbability;
+    }
+
+    // serialize the class to a string.
+    @Override
+    public String toString() {
+        return "ResolverTarget{"
+                + mRecencyScore + ", "
+                + mTimeSpentScore + ", "
+                + mLaunchScore + ", "
+                + mChooserScore + ", "
+                + mSelectProbability + "}";
+    }
+
+    // describes the kinds of special objects contained in this Parcelable instance's marshaled
+    // representation.
+    @Override
+    public int describeContents() {
+        return 0;
+    }
+
+    // flattens this object in to a Parcel.
+    @Override
+    public void writeToParcel(Parcel dest, int flags) {
+        dest.writeFloat(mRecencyScore);
+        dest.writeFloat(mTimeSpentScore);
+        dest.writeFloat(mLaunchScore);
+        dest.writeFloat(mChooserScore);
+        dest.writeFloat(mSelectProbability);
+    }
+
+    // creator definition for the class.
+    public static final Creator<ResolverTarget> CREATOR
+            = new Creator<ResolverTarget>() {
+        @Override
+        public ResolverTarget createFromParcel(Parcel source) {
+            return new ResolverTarget(source);
+        }
+
+        @Override
+        public ResolverTarget[] newArray(int size) {
+            return new ResolverTarget[size];
+        }
+    };
+}
diff --git a/core/java/com/android/internal/app/LRResolverRankerService.java b/core/java/com/android/internal/app/LRResolverRankerService.java
new file mode 100644
index 0000000..1cad7c7
--- /dev/null
+++ b/core/java/com/android/internal/app/LRResolverRankerService.java
@@ -0,0 +1,199 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.internal.app;
+
+import android.content.Context;
+import android.content.Intent;
+import android.content.SharedPreferences;
+import android.os.Environment;
+import android.os.IBinder;
+import android.os.storage.StorageManager;
+import android.service.resolver.ResolverRankerService;
+import android.service.resolver.ResolverTarget;
+import android.util.ArrayMap;
+import android.util.Log;
+
+import java.io.File;
+import java.util.Collection;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * A Logistic Regression based {@link android.service.resolver.ResolverRankerService}, to be used
+ * in {@link ResolverComparator}.
+ */
+public final class LRResolverRankerService extends ResolverRankerService {
+    private static final String TAG = "LRResolverRankerService";
+
+    private static final boolean DEBUG = false;
+
+    private static final String PARAM_SHARED_PREF_NAME = "resolver_ranker_params";
+    private static final String BIAS_PREF_KEY = "bias";
+    private static final String VERSION_PREF_KEY = "version";
+
+    private static final String LAUNCH_SCORE = "launch";
+    private static final String TIME_SPENT_SCORE = "timeSpent";
+    private static final String RECENCY_SCORE = "recency";
+    private static final String CHOOSER_SCORE = "chooser";
+
+    // parameters for a pre-trained model, to initialize the app ranker. When updating the
+    // pre-trained model, please update these params, as well as initModel().
+    private static final int CURRENT_VERSION = 1;
+    private static final float LEARNING_RATE = 0.0001f;
+    private static final float REGULARIZER_PARAM = 0.0001f;
+
+    private SharedPreferences mParamSharedPref;
+    private ArrayMap<String, Float> mFeatureWeights;
+    private float mBias;
+
+    @Override
+    public IBinder onBind(Intent intent) {
+        initModel();
+        return super.onBind(intent);
+    }
+
+    @Override
+    public void onPredictSharingProbabilities(List<ResolverTarget> targets) {
+        final int size = targets.size();
+        for (int i = 0; i < size; ++i) {
+            ResolverTarget target = targets.get(i);
+            ArrayMap<String, Float> features = getFeatures(target);
+            target.setSelectProbability(predict(features));
+        }
+    }
+
+    @Override
+    public void onTrainRankingModel(List<ResolverTarget> targets, int selectedPosition) {
+        final int size = targets.size();
+        if (selectedPosition < 0 || selectedPosition >= size) {
+            if (DEBUG) {
+                Log.d(TAG, "Invalid Position of Selected App " + selectedPosition);
+            }
+            return;
+        }
+        final ArrayMap<String, Float> positive = getFeatures(targets.get(selectedPosition));
+        final float positiveProbability = targets.get(selectedPosition).getSelectProbability();
+        final int targetSize = targets.size();
+        for (int i = 0; i < targetSize; ++i) {
+            if (i == selectedPosition) {
+                continue;
+            }
+            final ArrayMap<String, Float> negative = getFeatures(targets.get(i));
+            final float negativeProbability = targets.get(i).getSelectProbability();
+            if (negativeProbability > positiveProbability) {
+                update(negative, negativeProbability, false);
+                update(positive, positiveProbability, true);
+            }
+        }
+        commitUpdate();
+    }
+
+    private void initModel() {
+        mParamSharedPref = getParamSharedPref();
+        mFeatureWeights = new ArrayMap<>(4);
+        if (mParamSharedPref == null ||
+                mParamSharedPref.getInt(VERSION_PREF_KEY, 0) < CURRENT_VERSION) {
+            // Initializing the app ranker to a pre-trained model. When updating the pre-trained
+            // model, please increment CURRENT_VERSION, and update LEARNING_RATE and
+            // REGULARIZER_PARAM.
+            mBias = -1.6568f;
+            mFeatureWeights.put(LAUNCH_SCORE, 2.5543f);
+            mFeatureWeights.put(TIME_SPENT_SCORE, 2.8412f);
+            mFeatureWeights.put(RECENCY_SCORE, 0.269f);
+            mFeatureWeights.put(CHOOSER_SCORE, 4.2222f);
+        } else {
+            mBias = mParamSharedPref.getFloat(BIAS_PREF_KEY, 0.0f);
+            mFeatureWeights.put(LAUNCH_SCORE, mParamSharedPref.getFloat(LAUNCH_SCORE, 0.0f));
+            mFeatureWeights.put(
+                    TIME_SPENT_SCORE, mParamSharedPref.getFloat(TIME_SPENT_SCORE, 0.0f));
+            mFeatureWeights.put(RECENCY_SCORE, mParamSharedPref.getFloat(RECENCY_SCORE, 0.0f));
+            mFeatureWeights.put(CHOOSER_SCORE, mParamSharedPref.getFloat(CHOOSER_SCORE, 0.0f));
+        }
+    }
+
+    private ArrayMap<String, Float> getFeatures(ResolverTarget target) {
+        ArrayMap<String, Float> features = new ArrayMap<>(4);
+        features.put(RECENCY_SCORE, target.getRecencyScore());
+        features.put(TIME_SPENT_SCORE, target.getTimeSpentScore());
+        features.put(LAUNCH_SCORE, target.getLaunchScore());
+        features.put(CHOOSER_SCORE, target.getChooserScore());
+        return features;
+    }
+
+    private float predict(ArrayMap<String, Float> target) {
+        if (target == null) {
+            return 0.0f;
+        }
+        final int featureSize = target.size();
+        float sum = 0.0f;
+        for (int i = 0; i < featureSize; i++) {
+            String featureName = target.keyAt(i);
+            float weight = mFeatureWeights.getOrDefault(featureName, 0.0f);
+            sum += weight * target.valueAt(i);
+        }
+        return (float) (1.0 / (1.0 + Math.exp(-mBias - sum)));
+    }
+
+    private void update(ArrayMap<String, Float> target, float predict, boolean isSelected) {
+        if (target == null) {
+            return;
+        }
+        final int featureSize = target.size();
+        float error = isSelected ? 1.0f - predict : -predict;
+        for (int i = 0; i < featureSize; i++) {
+            String featureName = target.keyAt(i);
+            float currentWeight = mFeatureWeights.getOrDefault(featureName, 0.0f);
+            mBias += LEARNING_RATE * error;
+            currentWeight = currentWeight - LEARNING_RATE * REGULARIZER_PARAM * currentWeight +
+                    LEARNING_RATE * error * target.valueAt(i);
+            mFeatureWeights.put(featureName, currentWeight);
+        }
+        if (DEBUG) {
+            Log.d(TAG, "Weights: " + mFeatureWeights + " Bias: " + mBias);
+        }
+    }
+
+    private void commitUpdate() {
+        try {
+            SharedPreferences.Editor editor = mParamSharedPref.edit();
+            editor.putFloat(BIAS_PREF_KEY, mBias);
+            final int size = mFeatureWeights.size();
+            for (int i = 0; i < size; i++) {
+                editor.putFloat(mFeatureWeights.keyAt(i), mFeatureWeights.valueAt(i));
+            }
+            editor.putInt(VERSION_PREF_KEY, CURRENT_VERSION);
+            editor.apply();
+        } catch (Exception e) {
+            Log.e(TAG, "Failed to commit update" + e);
+        }
+    }
+
+    private SharedPreferences getParamSharedPref() {
+        // The package info in the context isn't initialized in the way it is for normal apps,
+        // so the standard, name-based context.getSharedPreferences doesn't work. Instead, we
+        // build the path manually below using the same policy that appears in ContextImpl.
+        if (DEBUG) {
+            Log.d(TAG, "Context Package Name: " + getPackageName());
+        }
+        final File prefsFile = new File(new File(
+                Environment.getDataUserCePackageDirectory(
+                        StorageManager.UUID_PRIVATE_INTERNAL, getUserId(), getPackageName()),
+                "shared_prefs"),
+                PARAM_SHARED_PREF_NAME + ".xml");
+        return getSharedPreferences(prefsFile, Context.MODE_PRIVATE);
+    }
+}
\ No newline at end of file
diff --git a/core/java/com/android/internal/app/ResolverActivity.java b/core/java/com/android/internal/app/ResolverActivity.java
index 3f1c9ad..622b708 100644
--- a/core/java/com/android/internal/app/ResolverActivity.java
+++ b/core/java/com/android/internal/app/ResolverActivity.java
@@ -530,6 +530,9 @@
             getMainThreadHandler().removeCallbacks(mPostListReadyRunnable);
             mPostListReadyRunnable = null;
         }
+        if (mAdapter != null && mAdapter.mResolverListController != null) {
+            mAdapter.mResolverListController.destroy();
+        }
     }
 
     @Override
diff --git a/core/java/com/android/internal/app/ResolverComparator.java b/core/java/com/android/internal/app/ResolverComparator.java
index 096fcb8..73b62a5 100644
--- a/core/java/com/android/internal/app/ResolverComparator.java
+++ b/core/java/com/android/internal/app/ResolverComparator.java
@@ -26,20 +26,34 @@
 import android.content.pm.ApplicationInfo;
 import android.content.pm.ComponentInfo;
 import android.content.pm.PackageManager;
+import android.content.pm.PackageManager.NameNotFoundException;
 import android.content.pm.ResolveInfo;
 import android.content.SharedPreferences;
+import android.content.ServiceConnection;
 import android.os.Environment;
+import android.os.Handler;
+import android.os.IBinder;
+import android.os.Looper;
+import android.os.Message;
+import android.os.RemoteException;
 import android.os.storage.StorageManager;
 import android.os.UserHandle;
+import android.service.resolver.IResolverRankerService;
+import android.service.resolver.IResolverRankerResult;
+import android.service.resolver.ResolverRankerService;
+import android.service.resolver.ResolverTarget;
 import android.text.TextUtils;
 import android.util.ArrayMap;
 import android.util.Log;
 import com.android.internal.app.ResolverActivity.ResolvedComponentInfo;
 
 import java.io.File;
+import java.lang.InterruptedException;
 import java.text.Collator;
 import java.util.ArrayList;
 import java.util.Comparator;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
@@ -61,11 +75,15 @@
 
     private static final float RECENCY_MULTIPLIER = 2.f;
 
-    // feature names used in ranking.
-    private static final String LAUNCH_SCORE = "launch";
-    private static final String TIME_SPENT_SCORE = "timeSpent";
-    private static final String RECENCY_SCORE = "recency";
-    private static final String CHOOSER_SCORE = "chooser";
+    // message types
+    private static final int RESOLVER_RANKER_SERVICE_RESULT = 0;
+    private static final int RESOLVER_RANKER_RESULT_TIMEOUT = 1;
+
+    // timeout for establishing connections with a ResolverRankerService.
+    private static final int CONNECTION_COST_TIMEOUT_MILLIS = 200;
+    // timeout for establishing connections with a ResolverRankerService, collecting features and
+    // predicting ranking scores.
+    private static final int WATCHDOG_TIMEOUT_MILLIS = 500;
 
     private final Collator mCollator;
     private final boolean mHttp;
@@ -74,18 +92,74 @@
     private final Map<String, UsageStats> mStats;
     private final long mCurrentTime;
     private final long mSinceTime;
-    private final LinkedHashMap<ComponentName, ScoredTarget> mScoredTargets = new LinkedHashMap<>();
+    private final LinkedHashMap<ComponentName, ResolverTarget> mTargetsDict = new LinkedHashMap<>();
     private final String mReferrerPackage;
+    private final Object mLock = new Object();
+    private ArrayList<ResolverTarget> mTargets;
     private String mContentType;
     private String[] mAnnotations;
     private String mAction;
-    private LogisticRegressionAppRanker mRanker;
+    private IResolverRankerService mRanker;
+    private ResolverRankerServiceConnection mConnection;
+    private AfterCompute mAfterCompute;
+    private Context mContext;
+    private CountDownLatch mConnectSignal;
 
-    public ResolverComparator(Context context, Intent intent, String referrerPackage) {
+    private final Handler mHandler = new Handler(Looper.getMainLooper()) {
+        public void handleMessage(Message msg) {
+            switch (msg.what) {
+                case RESOLVER_RANKER_SERVICE_RESULT:
+                    if (DEBUG) {
+                        Log.d(TAG, "RESOLVER_RANKER_SERVICE_RESULT");
+                    }
+                    if (mHandler.hasMessages(RESOLVER_RANKER_RESULT_TIMEOUT)) {
+                        if (msg.obj != null) {
+                            final List<ResolverTarget> receivedTargets =
+                                    (List<ResolverTarget>) msg.obj;
+                            if (receivedTargets != null && mTargets != null
+                                    && receivedTargets.size() == mTargets.size()) {
+                                final int size = mTargets.size();
+                                for (int i = 0; i < size; ++i) {
+                                    mTargets.get(i).setSelectProbability(
+                                            receivedTargets.get(i).getSelectProbability());
+                                }
+                            } else {
+                                Log.e(TAG, "Sizes of sent and received ResolverTargets diff.");
+                            }
+                        } else {
+                            Log.e(TAG, "Receiving null prediction results.");
+                        }
+                        mHandler.removeMessages(RESOLVER_RANKER_RESULT_TIMEOUT);
+                        mAfterCompute.afterCompute();
+                    }
+                    break;
+
+                case RESOLVER_RANKER_RESULT_TIMEOUT:
+                    if (DEBUG) {
+                        Log.d(TAG, "RESOLVER_RANKER_RESULT_TIMEOUT; unbinding services");
+                    }
+                    mHandler.removeMessages(RESOLVER_RANKER_SERVICE_RESULT);
+                    mAfterCompute.afterCompute();
+                    break;
+
+                default:
+                    super.handleMessage(msg);
+            }
+        }
+    };
+
+    public interface AfterCompute {
+        public void afterCompute ();
+    }
+
+    public ResolverComparator(Context context, Intent intent, String referrerPackage,
+                              AfterCompute afterCompute) {
         mCollator = Collator.getInstance(context.getResources().getConfiguration().locale);
         String scheme = intent.getScheme();
         mHttp = "http".equals(scheme) || "https".equals(scheme);
         mReferrerPackage = referrerPackage;
+        mAfterCompute = afterCompute;
+        mContext = context;
 
         mPm = context.getPackageManager();
         mUsm = (UsageStatsManager) context.getSystemService(Context.USAGE_STATS_SERVICE);
@@ -96,9 +170,9 @@
         mContentType = intent.getType();
         getContentAnnotations(intent);
         mAction = intent.getAction();
-        mRanker = new LogisticRegressionAppRanker(context);
     }
 
+    // get annotations of content from intent.
     public void getContentAnnotations(Intent intent) {
         ArrayList<String> annotations = intent.getStringArrayListExtra(
                 Intent.EXTRA_CONTENT_ANNOTATIONS);
@@ -114,20 +188,24 @@
         }
     }
 
+    public void setCallBack(AfterCompute afterCompute) {
+        mAfterCompute = afterCompute;
+    }
+
+    // compute features for each target according to usage stats of targets.
     public void compute(List<ResolvedComponentInfo> targets) {
-        mScoredTargets.clear();
+        reset();
 
         final long recentSinceTime = mCurrentTime - RECENCY_TIME_PERIOD;
 
-        long mostRecentlyUsedTime = recentSinceTime + 1;
-        long mostTimeSpent = 1;
-        int mostLaunched = 1;
-        int mostSelected = 1;
+        float mostRecencyScore = 1.0f;
+        float mostTimeSpentScore = 1.0f;
+        float mostLaunchScore = 1.0f;
+        float mostChooserScore = 1.0f;
 
         for (ResolvedComponentInfo target : targets) {
-            final ScoredTarget scoredTarget
-                    = new ScoredTarget(target.getResolveInfoAt(0).activityInfo);
-            mScoredTargets.put(target.name, scoredTarget);
+            final ResolverTarget resolverTarget = new ResolverTarget();
+            mTargetsDict.put(target.name, resolverTarget);
             final UsageStats pkStats = mStats.get(target.name.getPackageName());
             if (pkStats != null) {
                 // Only count recency for apps that weren't the caller
@@ -135,31 +213,33 @@
                 // Persistent processes muck this up, so omit them too.
                 if (!target.name.getPackageName().equals(mReferrerPackage)
                         && !isPersistentProcess(target)) {
-                    final long lastTimeUsed = pkStats.getLastTimeUsed();
-                    scoredTarget.lastTimeUsed = lastTimeUsed;
-                    if (lastTimeUsed > mostRecentlyUsedTime) {
-                        mostRecentlyUsedTime = lastTimeUsed;
+                    final float recencyScore =
+                            (float) Math.max(pkStats.getLastTimeUsed() - recentSinceTime, 0);
+                    resolverTarget.setRecencyScore(recencyScore);
+                    if (recencyScore > mostRecencyScore) {
+                        mostRecencyScore = recencyScore;
                     }
                 }
-                final long timeSpent = pkStats.getTotalTimeInForeground();
-                scoredTarget.timeSpent = timeSpent;
-                if (timeSpent > mostTimeSpent) {
-                    mostTimeSpent = timeSpent;
+                final float timeSpentScore = (float) pkStats.getTotalTimeInForeground();
+                resolverTarget.setTimeSpentScore(timeSpentScore);
+                if (timeSpentScore > mostTimeSpentScore) {
+                    mostTimeSpentScore = timeSpentScore;
                 }
-                final int launched = pkStats.mLaunchCount;
-                scoredTarget.launchCount = launched;
-                if (launched > mostLaunched) {
-                    mostLaunched = launched;
+                final float launchScore = (float) pkStats.mLaunchCount;
+                resolverTarget.setLaunchScore(launchScore);
+                if (launchScore > mostLaunchScore) {
+                    mostLaunchScore = launchScore;
                 }
 
-                int selected = 0;
+                float chooserScore = 0.0f;
                 if (pkStats.mChooserCounts != null && mAction != null
                         && pkStats.mChooserCounts.get(mAction) != null) {
-                    selected = pkStats.mChooserCounts.get(mAction).getOrDefault(mContentType, 0);
+                    chooserScore = (float) pkStats.mChooserCounts.get(mAction)
+                            .getOrDefault(mContentType, 0);
                     if (mAnnotations != null) {
                         final int size = mAnnotations.length;
                         for (int i = 0; i < size; i++) {
-                            selected += pkStats.mChooserCounts.get(mAction)
+                            chooserScore += (float) pkStats.mChooserCounts.get(mAction)
                                     .getOrDefault(mAnnotations[i], 0);
                         }
                     }
@@ -169,44 +249,37 @@
                         Log.d(TAG, "Action type is null");
                     } else {
                         Log.d(TAG, "Chooser Count of " + mAction + ":" +
-                                target.name.getPackageName() + " is " + Integer.toString(selected));
+                                target.name.getPackageName() + " is " +
+                                Float.toString(chooserScore));
                     }
                 }
-                scoredTarget.chooserCount = selected;
-                if (selected > mostSelected) {
-                    mostSelected = selected;
+                resolverTarget.setChooserScore(chooserScore);
+                if (chooserScore > mostChooserScore) {
+                    mostChooserScore = chooserScore;
                 }
             }
         }
 
-
         if (DEBUG) {
-            Log.d(TAG, "compute - mostRecentlyUsedTime: " + mostRecentlyUsedTime
-                    + " mostTimeSpent: " + mostTimeSpent
-                    + " recentSinceTime: " + recentSinceTime
-                    + " mostLaunched: " + mostLaunched);
+            Log.d(TAG, "compute - mostRecencyScore: " + mostRecencyScore
+                    + " mostTimeSpentScore: " + mostTimeSpentScore
+                    + " mostLaunchScore: " + mostLaunchScore
+                    + " mostChooserScore: " + mostChooserScore);
         }
 
-        for (ScoredTarget target : mScoredTargets.values()) {
-            final float recency = (float) Math.max(target.lastTimeUsed - recentSinceTime, 0)
-                    / (mostRecentlyUsedTime - recentSinceTime);
-            target.setFeatures((float) target.launchCount / mostLaunched,
-                    (float) target.timeSpent / mostTimeSpent,
-                    recency * recency * RECENCY_MULTIPLIER,
-                    (float) target.chooserCount / mostSelected);
-            target.selectProb = mRanker.predict(target.getFeatures());
+        mTargets = new ArrayList<>(mTargetsDict.values());
+        for (ResolverTarget target : mTargets) {
+            final float recency = target.getRecencyScore() / mostRecencyScore;
+            setFeatures(target, recency * recency * RECENCY_MULTIPLIER,
+                    target.getLaunchScore() / mostLaunchScore,
+                    target.getTimeSpentScore() / mostTimeSpentScore,
+                    target.getChooserScore() / mostChooserScore);
+            addDefaultSelectProbability(target);
             if (DEBUG) {
                 Log.d(TAG, "Scores: " + target);
             }
         }
-    }
-
-    static boolean isPersistentProcess(ResolvedComponentInfo rci) {
-        if (rci != null && rci.getCount() > 0) {
-            return (rci.getResolveInfoAt(0).activityInfo.applicationInfo.flags &
-                    ApplicationInfo.FLAG_PERSISTENT) != 0;
-        }
-        return false;
+        predictSelectProbabilities(mTargets);
     }
 
     @Override
@@ -245,16 +318,16 @@
         // Pinned items stay stable within a normal lexical sort and ignore scoring.
         if (!lPinned && !rPinned) {
             if (mStats != null) {
-                final ScoredTarget lhsTarget = mScoredTargets.get(new ComponentName(
+                final ResolverTarget lhsTarget = mTargetsDict.get(new ComponentName(
                         lhs.activityInfo.packageName, lhs.activityInfo.name));
-                final ScoredTarget rhsTarget = mScoredTargets.get(new ComponentName(
+                final ResolverTarget rhsTarget = mTargetsDict.get(new ComponentName(
                         rhs.activityInfo.packageName, rhs.activityInfo.name));
 
-                final int selectProbDiff = Float.compare(
-                        rhsTarget.selectProb, lhsTarget.selectProb);
+                final int selectProbabilityDiff = Float.compare(
+                        rhsTarget.getSelectProbability(), lhsTarget.getSelectProbability());
 
-                if (selectProbDiff != 0) {
-                    return selectProbDiff > 0 ? 1 : -1;
+                if (selectProbabilityDiff != 0) {
+                    return selectProbabilityDiff > 0 ? 1 : -1;
                 }
             }
         }
@@ -268,177 +341,234 @@
     }
 
     public float getScore(ComponentName name) {
-        final ScoredTarget target = mScoredTargets.get(name);
+        final ResolverTarget target = mTargetsDict.get(name);
         if (target != null) {
-            return target.selectProb;
+            return target.getSelectProbability();
         }
         return 0;
     }
 
-    static class ScoredTarget {
-        public final ComponentInfo componentInfo;
-        public long lastTimeUsed;
-        public long timeSpent;
-        public long launchCount;
-        public long chooserCount;
-        public ArrayMap<String, Float> features;
-        public float selectProb;
-
-        public ScoredTarget(ComponentInfo ci) {
-            componentInfo = ci;
-            features = new ArrayMap<>(5);
-        }
-
-        @Override
-        public String toString() {
-            return "ScoredTarget{" + componentInfo
-                    + " lastTimeUsed: " + lastTimeUsed
-                    + " timeSpent: " + timeSpent
-                    + " launchCount: " + launchCount
-                    + " chooserCount: " + chooserCount
-                    + " selectProb: " + selectProb
-                    + "}";
-        }
-
-        public void setFeatures(float launchCountScore, float usageTimeScore, float recencyScore,
-                                float chooserCountScore) {
-            features.put(LAUNCH_SCORE, launchCountScore);
-            features.put(TIME_SPENT_SCORE, usageTimeScore);
-            features.put(RECENCY_SCORE, recencyScore);
-            features.put(CHOOSER_SCORE, chooserCountScore);
-        }
-
-        public ArrayMap<String, Float> getFeatures() {
-            return features;
-        }
-    }
-
     public void updateChooserCounts(String packageName, int userId, String action) {
         if (mUsm != null) {
             mUsm.reportChooserSelection(packageName, userId, mContentType, mAnnotations, action);
         }
     }
 
+    // update ranking model when the connection to it is valid.
     public void updateModel(ComponentName componentName) {
-        if (mScoredTargets == null || componentName == null ||
-                !mScoredTargets.containsKey(componentName)) {
-            return;
-        }
-        ScoredTarget selected = mScoredTargets.get(componentName);
-        for (ComponentName targetComponent : mScoredTargets.keySet()) {
-            if (targetComponent.equals(componentName)) {
-                continue;
-            }
-            ScoredTarget target = mScoredTargets.get(targetComponent);
-            // A potential point of optimization. Save updates or derive a closed form for the
-            // positive case, to avoid calculating them repeatedly.
-            if (target.selectProb >= selected.selectProb) {
-                mRanker.update(target.getFeatures(), target.selectProb, false);
-                mRanker.update(selected.getFeatures(), selected.selectProb, true);
+        synchronized (mLock) {
+            if (mRanker != null) {
+                try {
+                    int selectedPos = new ArrayList<ComponentName>(mTargetsDict.keySet())
+                            .indexOf(componentName);
+                    if (selectedPos > 0) {
+                        mRanker.train(mTargets, selectedPos);
+                    } else {
+                        if (DEBUG) {
+                            Log.d(TAG, "Selected a unknown component: " + componentName);
+                        }
+                    }
+                } catch (RemoteException e) {
+                    Log.e(TAG, "Error in Train: " + e);
+                }
+            } else {
+                if (DEBUG) {
+                    Log.d(TAG, "Ranker is null; skip updateModel.");
+                }
             }
         }
-        mRanker.commitUpdate();
     }
 
-    class LogisticRegressionAppRanker {
-        private static final String PARAM_SHARED_PREF_NAME = "resolver_ranker_params";
-        private static final String BIAS_PREF_KEY = "bias";
-        private static final String VERSION_PREF_KEY = "version";
-
-        // parameters for a pre-trained model, to initialize the app ranker. When updating the
-        // pre-trained model, please update these params, as well as initModel().
-        private static final int CURRENT_VERSION = 1;
-        private static final float LEARNING_RATE = 0.0001f;
-        private static final float REGULARIZER_PARAM = 0.0001f;
-
-        private SharedPreferences mParamSharedPref;
-        private ArrayMap<String, Float> mFeatureWeights;
-        private float mBias;
-
-        public LogisticRegressionAppRanker(Context context) {
-            mParamSharedPref = getParamSharedPref(context);
-            initModel();
+    // unbind the service and clear unhandled messges.
+    public void destroy() {
+        mHandler.removeMessages(RESOLVER_RANKER_SERVICE_RESULT);
+        mHandler.removeMessages(RESOLVER_RANKER_RESULT_TIMEOUT);
+        if (mConnection != null) {
+            mContext.unbindService(mConnection);
+            mConnection.destroy();
         }
-
-        public float predict(ArrayMap<String, Float> target) {
-            if (target == null) {
-                return 0.0f;
-            }
-            final int featureSize = target.size();
-            float sum = 0.0f;
-            for (int i = 0; i < featureSize; i++) {
-                String featureName = target.keyAt(i);
-                float weight = mFeatureWeights.getOrDefault(featureName, 0.0f);
-                sum += weight * target.valueAt(i);
-            }
-            return (float) (1.0 / (1.0 + Math.exp(-mBias - sum)));
+        if (DEBUG) {
+            Log.d(TAG, "Unbinded Resolver Ranker.");
         }
+    }
 
-        public void update(ArrayMap<String, Float> target, float predict, boolean isSelected) {
-            if (target == null) {
+    // connect to a ranking service.
+    private void initRanker(Context context) {
+        synchronized (mLock) {
+            if (mConnection != null && mRanker != null) {
+                if (DEBUG) {
+                    Log.d(TAG, "Ranker still exists; reusing the existing one.");
+                }
                 return;
             }
-            final int featureSize = target.size();
-            float error = isSelected ? 1.0f - predict : -predict;
-            for (int i = 0; i < featureSize; i++) {
-                String featureName = target.keyAt(i);
-                float currentWeight = mFeatureWeights.getOrDefault(featureName, 0.0f);
-                mBias += LEARNING_RATE * error;
-                currentWeight = currentWeight - LEARNING_RATE * REGULARIZER_PARAM * currentWeight +
-                        LEARNING_RATE * error * target.valueAt(i);
-                mFeatureWeights.put(featureName, currentWeight);
+        }
+        Intent intent = resolveRankerService();
+        if (intent == null) {
+            return;
+        }
+        mConnectSignal = new CountDownLatch(1);
+        mConnection = new ResolverRankerServiceConnection(mConnectSignal);
+        context.bindServiceAsUser(intent, mConnection, Context.BIND_AUTO_CREATE, UserHandle.SYSTEM);
+    }
+
+    // resolve the service for ranking.
+    private Intent resolveRankerService() {
+        Intent intent = new Intent(ResolverRankerService.SERVICE_INTERFACE);
+        final List<ResolveInfo> resolveInfos = mPm.queryIntentServices(intent, 0);
+        for (ResolveInfo resolveInfo : resolveInfos) {
+            if (resolveInfo == null || resolveInfo.serviceInfo == null
+                    || resolveInfo.serviceInfo.applicationInfo == null) {
+                if (DEBUG) {
+                    Log.d(TAG, "Failed to retrieve a ranker: " + resolveInfo);
+                }
+                continue;
+            }
+            ComponentName componentName = new ComponentName(
+                    resolveInfo.serviceInfo.applicationInfo.packageName,
+                    resolveInfo.serviceInfo.name);
+            try {
+                final String perm = mPm.getServiceInfo(componentName, 0).permission;
+                if (!ResolverRankerService.BIND_PERMISSION.equals(perm)) {
+                    Log.w(TAG, "ResolverRankerService " + componentName + " does not require"
+                            + " permission " + ResolverRankerService.BIND_PERMISSION
+                            + " - this service will not be queried for ResolverComparator."
+                            + " add android:permission=\""
+                            + ResolverRankerService.BIND_PERMISSION + "\""
+                            + " to the <service> tag for " + componentName
+                            + " in the manifest.");
+                    continue;
+                }
+            } catch (NameNotFoundException e) {
+                Log.e(TAG, "Could not look up service " + componentName
+                        + "; component name not found");
+                continue;
             }
             if (DEBUG) {
-                Log.d(TAG, "Weights: " + mFeatureWeights + " Bias: " + mBias);
+                Log.d(TAG, "Succeeded to retrieve a ranker: " + componentName);
             }
+            intent.setComponent(componentName);
+            return intent;
+        }
+        return null;
+    }
+
+    // set a watchdog, to avoid waiting for ranking service for too long.
+    private void startWatchDog(int timeOutLimit) {
+        if (DEBUG) Log.d(TAG, "Setting watchdog timer for " + timeOutLimit + "ms");
+        if (mHandler == null) {
+            Log.d(TAG, "Error: Handler is Null; Needs to be initialized.");
+        }
+        mHandler.sendEmptyMessageDelayed(RESOLVER_RANKER_RESULT_TIMEOUT, timeOutLimit);
+    }
+
+    private class ResolverRankerServiceConnection implements ServiceConnection {
+        private final CountDownLatch mConnectSignal;
+
+        public ResolverRankerServiceConnection(CountDownLatch connectSignal) {
+            mConnectSignal = connectSignal;
         }
 
-        public void commitUpdate() {
-            SharedPreferences.Editor editor = mParamSharedPref.edit();
-            editor.putFloat(BIAS_PREF_KEY, mBias);
-            final int size = mFeatureWeights.size();
-            for (int i = 0; i < size; i++) {
-                editor.putFloat(mFeatureWeights.keyAt(i), mFeatureWeights.valueAt(i));
+        public final IResolverRankerResult resolverRankerResult =
+                new IResolverRankerResult.Stub() {
+            @Override
+            public void sendResult(List<ResolverTarget> targets) throws RemoteException {
+                if (DEBUG) {
+                    Log.d(TAG, "Sending Result back to Resolver: " + targets);
+                }
+                synchronized (mLock) {
+                    final Message msg = Message.obtain();
+                    msg.what = RESOLVER_RANKER_SERVICE_RESULT;
+                    msg.obj = targets;
+                    mHandler.sendMessage(msg);
+                }
             }
-            editor.putInt(VERSION_PREF_KEY, CURRENT_VERSION);
-            editor.apply();
-        }
+        };
 
-        private SharedPreferences getParamSharedPref(Context context) {
-            // The package info in the context isn't initialized in the way it is for normal apps,
-            // so the standard, name-based context.getSharedPreferences doesn't work. Instead, we
-            // build the path manually below using the same policy that appears in ContextImpl.
+        @Override
+        public void onServiceConnected(ComponentName name, IBinder service) {
             if (DEBUG) {
-                Log.d(TAG, "Context Package Name: " + context.getPackageName());
+                Log.d(TAG, "onServiceConnected: " + name);
             }
-            final File prefsFile = new File(new File(
-                    Environment.getDataUserCePackageDirectory(StorageManager.UUID_PRIVATE_INTERNAL,
-                            context.getUserId(), context.getPackageName()),
-                    "shared_prefs"),
-                    PARAM_SHARED_PREF_NAME + ".xml");
-            return context.getSharedPreferences(prefsFile, Context.MODE_PRIVATE);
+            synchronized (mLock) {
+                mRanker = IResolverRankerService.Stub.asInterface(service);
+                mConnectSignal.countDown();
+            }
         }
 
-        private void initModel() {
-            mFeatureWeights = new ArrayMap<>(4);
-            if (mParamSharedPref == null ||
-                    mParamSharedPref.getInt(VERSION_PREF_KEY, 0) < CURRENT_VERSION) {
-                // Initializing the app ranker to a pre-trained model. When updating the pre-trained
-                // model, please increment CURRENT_VERSION, and update LEARNING_RATE and
-                // REGULARIZER_PARAM.
-                mBias = -1.6568f;
-                mFeatureWeights.put(LAUNCH_SCORE, 2.5543f);
-                mFeatureWeights.put(TIME_SPENT_SCORE, 2.8412f);
-                mFeatureWeights.put(RECENCY_SCORE, 0.269f);
-                mFeatureWeights.put(CHOOSER_SCORE, 4.2222f);
-            } else {
-                mBias = mParamSharedPref.getFloat(BIAS_PREF_KEY, 0.0f);
-                mFeatureWeights.put(LAUNCH_SCORE, mParamSharedPref.getFloat(LAUNCH_SCORE, 0.0f));
-                mFeatureWeights.put(
-                        TIME_SPENT_SCORE, mParamSharedPref.getFloat(TIME_SPENT_SCORE, 0.0f));
-                mFeatureWeights.put(RECENCY_SCORE, mParamSharedPref.getFloat(RECENCY_SCORE, 0.0f));
-                mFeatureWeights.put(CHOOSER_SCORE, mParamSharedPref.getFloat(CHOOSER_SCORE, 0.0f));
+        @Override
+        public void onServiceDisconnected(ComponentName name) {
+            if (DEBUG) {
+                Log.d(TAG, "onServiceDisconnected: " + name);
+            }
+            synchronized (mLock) {
+                destroy();
             }
         }
+
+        public void destroy() {
+            synchronized (mLock) {
+                mRanker = null;
+            }
+        }
+    }
+
+    private void reset() {
+        mTargetsDict.clear();
+        mTargets = null;
+        startWatchDog(WATCHDOG_TIMEOUT_MILLIS);
+        initRanker(mContext);
+    }
+
+    // predict select probabilities if ranking service is valid.
+    private void predictSelectProbabilities(List<ResolverTarget> targets) {
+        if (mConnection == null) {
+            if (DEBUG) {
+                Log.d(TAG, "Has not found valid ResolverRankerService; Skip Prediction");
+            }
+            return;
+        } else {
+            try {
+                mConnectSignal.await(CONNECTION_COST_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS);
+                synchronized (mLock) {
+                    if (mRanker != null) {
+                        mRanker.predict(targets, mConnection.resolverRankerResult);
+                        return;
+                    } else {
+                        if (DEBUG) {
+                            Log.d(TAG, "Ranker has not been initialized; skip predict.");
+                        }
+                    }
+                }
+            } catch (InterruptedException e) {
+                Log.e(TAG, "Error in Wait for Service Connection.");
+            } catch (RemoteException e) {
+                Log.e(TAG, "Error in Predict: " + e);
+            }
+        }
+        mAfterCompute.afterCompute();
+    }
+
+    // adds select prob as the default values, according to a pre-trained Logistic Regression model.
+    private void addDefaultSelectProbability(ResolverTarget target) {
+        float sum = 2.5543f * target.getLaunchScore() + 2.8412f * target.getTimeSpentScore() +
+                0.269f * target.getRecencyScore() + 4.2222f * target.getChooserScore();
+        target.setSelectProbability((float) (1.0 / (1.0 + Math.exp(1.6568f - sum))));
+    }
+
+    // sets features for each target
+    private void setFeatures(ResolverTarget target, float recencyScore, float launchScore,
+                             float timeSpentScore, float chooserScore) {
+        target.setRecencyScore(recencyScore);
+        target.setLaunchScore(launchScore);
+        target.setTimeSpentScore(timeSpentScore);
+        target.setChooserScore(chooserScore);
+    }
+
+    static boolean isPersistentProcess(ResolvedComponentInfo rci) {
+        if (rci != null && rci.getCount() > 0) {
+            return (rci.getResolveInfoAt(0).activityInfo.applicationInfo.flags &
+                    ApplicationInfo.FLAG_PERSISTENT) != 0;
+        }
+        return false;
     }
 }
diff --git a/core/java/com/android/internal/app/ResolverListController.java b/core/java/com/android/internal/app/ResolverListController.java
index 4071ff4..e8bebb7 100644
--- a/core/java/com/android/internal/app/ResolverListController.java
+++ b/core/java/com/android/internal/app/ResolverListController.java
@@ -32,8 +32,10 @@
 import android.util.Log;
 import com.android.internal.annotations.VisibleForTesting;
 
+import java.lang.InterruptedException;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.concurrent.CountDownLatch;
 import java.util.List;
 
 /**
@@ -205,14 +207,42 @@
         return listToReturn;
     }
 
+    private class ComputeCallback implements ResolverComparator.AfterCompute {
+
+        private CountDownLatch mFinishComputeSignal;
+
+        public ComputeCallback(CountDownLatch finishComputeSignal) {
+            mFinishComputeSignal = finishComputeSignal;
+        }
+
+        public void afterCompute () {
+            mFinishComputeSignal.countDown();
+        }
+    }
+
     @VisibleForTesting
     @WorkerThread
     public void sort(List<ResolverActivity.ResolvedComponentInfo> inputList) {
+        final CountDownLatch finishComputeSignal = new CountDownLatch(1);
+        ComputeCallback callback = new ComputeCallback(finishComputeSignal);
         if (mResolverComparator == null) {
-            mResolverComparator = new ResolverComparator(mContext, mTargetIntent, mReferrerPackage);
+            mResolverComparator =
+                    new ResolverComparator(mContext, mTargetIntent, mReferrerPackage, callback);
+        } else {
+            mResolverComparator.setCallBack(callback);
         }
-        mResolverComparator.compute(inputList);
-        Collections.sort(inputList, mResolverComparator);
+        try {
+            long beforeRank = System.currentTimeMillis();
+            mResolverComparator.compute(inputList);
+            finishComputeSignal.await();
+            Collections.sort(inputList, mResolverComparator);
+            long afterRank = System.currentTimeMillis();
+            if (DEBUG) {
+                Log.d(TAG, "Time Cost: " + Long.toString(afterRank - beforeRank));
+            }
+        } catch (InterruptedException e) {
+            Log.e(TAG, "Compute & Sort was interrupted: " + e);
+        }
     }
 
     private static boolean isSameResolvedComponent(ResolveInfo a,
@@ -233,7 +263,7 @@
     @VisibleForTesting
     public float getScore(ResolverActivity.DisplayResolveInfo target) {
         if (mResolverComparator == null) {
-            mResolverComparator = new ResolverComparator(mContext, mTargetIntent, mReferrerPackage);
+            return 0.0f;
         }
         return mResolverComparator.getScore(target.getResolvedComponentName());
     }
@@ -249,4 +279,10 @@
             mResolverComparator.updateChooserCounts(packageName, userId, action);
         }
     }
+
+    public void destroy() {
+        if (mResolverComparator != null) {
+            mResolverComparator.destroy();
+        }
+    }
 }
diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index 313041e..cf6f37f 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -3130,6 +3130,15 @@
     <permission android:name="android.permission.BIND_CHOOSER_TARGET_SERVICE"
         android:protectionLevel="signature" />
 
+    <!-- @SystemApi Must be required by services that extend
+         {@link android.service.resolver.ResolverRankerService}, to ensure that only the system can
+         bind to them.
+         <p>Protection level: signature
+         @hide
+    -->
+    <permission android:name="android.permission.BIND_RESOLVER_RANKER_SERVICE"
+        android:protectionLevel="signature" />
+
     <!-- Must be required by a {@link
          android.service.notification.ConditionProviderService},
          to ensure that only the system can bind to it.
@@ -3641,6 +3650,13 @@
                  android:permission="android.permission.BIND_JOB_SERVICE" >
         </service>
 
+        <service android:name="com.android.internal.app.LRResolverRankerService"
+            android:permission="android.permission.BIND_RESOLVER_RANKER_SERVICE"
+            android:priority="-1" >
+            <intent-filter>
+                <action android:name="android.service.resolver.ResolverRankerService" />
+            </intent-filter>
+        </service>
     </application>
 
 </manifest>
diff --git a/packages/SystemUI/AndroidManifest.xml b/packages/SystemUI/AndroidManifest.xml
index 1147f16..bf39bc4 100644
--- a/packages/SystemUI/AndroidManifest.xml
+++ b/packages/SystemUI/AndroidManifest.xml
@@ -183,6 +183,9 @@
     <!-- to control accessibility volume -->
     <uses-permission android:name="android.permission.CHANGE_ACCESSIBILITY_VOLUME" />
 
+    <!-- to access ResolverRankerServices -->
+    <uses-permission android:name="android.permission.BIND_RESOLVER_RANKER_SERVICE" />
+
     <application
         android:name=".SystemUIApplication"
         android:persistent="true"