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diff --git a/java/src/com/android/inputmethod/latin/personalization/DecayingExpandableBinaryDictionaryBase.java b/java/src/com/android/inputmethod/latin/personalization/DecayingExpandableBinaryDictionaryBase.java
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+++ b/java/src/com/android/inputmethod/latin/personalization/DecayingExpandableBinaryDictionaryBase.java
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+/*
+ * Copyright (C) 2013 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.inputmethod.latin.personalization;
+
+import android.content.Context;
+import android.content.SharedPreferences;
+import android.util.Log;
+
+import com.android.inputmethod.annotations.UsedForTesting;
+import com.android.inputmethod.latin.Constants;
+import com.android.inputmethod.latin.ExpandableBinaryDictionary;
+import com.android.inputmethod.latin.LatinImeLogger;
+import com.android.inputmethod.latin.makedict.DictDecoder;
+import com.android.inputmethod.latin.makedict.FormatSpec;
+import com.android.inputmethod.latin.settings.Settings;
+import com.android.inputmethod.latin.utils.CollectionUtils;
+import com.android.inputmethod.latin.utils.UserHistoryDictIOUtils;
+import com.android.inputmethod.latin.utils.UserHistoryDictIOUtils.OnAddWordListener;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * This class is a base class of a dictionary that supports decaying for the personalized language
+ * model.
+ */
+public abstract class DecayingExpandableBinaryDictionaryBase extends ExpandableBinaryDictionary {
+    private static final String TAG = DecayingExpandableBinaryDictionaryBase.class.getSimpleName();
+    public static final boolean DBG_SAVE_RESTORE = false;
+    private static final boolean DBG_STRESS_TEST = false;
+    private static final boolean PROFILE_SAVE_RESTORE = LatinImeLogger.sDBG;
+
+    /** Any pair being typed or picked */
+    public static final int FREQUENCY_FOR_TYPED = 2;
+
+    /** Locale for which this user history dictionary is storing words */
+    private final String mLocale;
+
+    private final String mFileName;
+
+    private final SharedPreferences mPrefs;
+
+    private final ArrayList<PersonalizationDictionaryUpdateSession> mSessions =
+            CollectionUtils.newArrayList();
+
+    // Should always be false except when we use this class for test
+    @UsedForTesting boolean mIsTest = false;
+
+    /* package */ DecayingExpandableBinaryDictionaryBase(final Context context,
+            final String locale, final SharedPreferences sp, final String dictionaryType,
+            final String fileName) {
+        super(context, fileName, dictionaryType, true);
+        mLocale = locale;
+        mFileName = fileName;
+        mPrefs = sp;
+        if (mLocale != null && mLocale.length() > 1) {
+            asyncLoadDictionaryToMemory();
+            reloadDictionaryIfRequired();
+        }
+    }
+
+    @Override
+    public void close() {
+        if (!ExpandableBinaryDictionary.ENABLE_BINARY_DICTIONARY_DYNAMIC_UPDATE) {
+            closeBinaryDictionary();
+        }
+        // Flush pending writes.
+        // TODO: Remove after this class become to use a dynamic binary dictionary.
+        asyncFlashAllBinaryDictionary();
+        Settings.writeLastUserHistoryWriteTime(mPrefs, mLocale);
+    }
+
+    @Override
+    protected Map<String, String> getHeaderAttributeMap() {
+        HashMap<String, String> attributeMap = new HashMap<String, String>();
+        attributeMap.put(FormatSpec.FileHeader.SUPPORTS_DYNAMIC_UPDATE_ATTRIBUTE,
+                FormatSpec.FileHeader.ATTRIBUTE_VALUE_TRUE);
+        attributeMap.put(FormatSpec.FileHeader.USES_FORGETTING_CURVE_ATTRIBUTE,
+                FormatSpec.FileHeader.ATTRIBUTE_VALUE_TRUE);
+        return attributeMap;
+    }
+
+    @Override
+    protected boolean hasContentChanged() {
+        return false;
+    }
+
+    @Override
+    protected boolean needsToReloadBeforeWriting() {
+        return false;
+    }
+
+    /**
+     * Return whether the passed charsequence is in the dictionary.
+     */
+    @Override
+    public boolean isValidWord(final String word) {
+     // Words included only in the user history should be treated as not in dictionary words.
+        return false;
+    }
+
+    /**
+     * Pair will be added to the personalization prediction dictionary.
+     *
+     * The first word may be null. That means we don't know the context, in other words,
+     * it's only a unigram. The first word may also be an empty string : this means start
+     * context, as in beginning of a sentence for example.
+     * The second word may not be null (a NullPointerException would be thrown).
+     */
+    public void addToPersonalizationPredictionDictionary(
+            final String word0, final String word1, final boolean isValid) {
+        if (word1.length() >= Constants.DICTIONARY_MAX_WORD_LENGTH ||
+                (word0 != null && word0.length() >= Constants.DICTIONARY_MAX_WORD_LENGTH)) {
+            return;
+        }
+        addWordDynamically(word1, null /* the "shortcut" parameter is null */, FREQUENCY_FOR_TYPED,
+                false /* isNotAWord */);
+        // Do not insert a word as a bigram of itself
+        if (word1.equals(word0)) {
+            return;
+        }
+        if (null != word0) {
+            addBigramDynamically(word0, word1, FREQUENCY_FOR_TYPED, isValid);
+        }
+    }
+
+    public void cancelAddingUserHistory(final String word0, final String word1) {
+        removeBigramDynamically(word0, word1);
+    }
+
+    @Override
+    protected void loadDictionaryAsync() {
+        final int[] profTotalCount = { 0 };
+        final String locale = getLocale();
+        if (DBG_STRESS_TEST) {
+            try {
+                Log.w(TAG, "Start stress in loading: " + locale);
+                Thread.sleep(15000);
+                Log.w(TAG, "End stress in loading");
+            } catch (InterruptedException e) {
+            }
+        }
+        final long last = Settings.readLastUserHistoryWriteTime(mPrefs, locale);
+        final long now = System.currentTimeMillis();
+        final ExpandableBinaryDictionary dictionary = this;
+        final OnAddWordListener listener = new OnAddWordListener() {
+            @Override
+            public void setUnigram(final String word, final String shortcutTarget,
+                    final int frequency) {
+                if (DBG_SAVE_RESTORE) {
+                    Log.d(TAG, "load unigram: " + word + "," + frequency);
+                }
+                addWord(word, shortcutTarget, frequency, false /* isNotAWord */);
+                ++profTotalCount[0];
+            }
+
+            @Override
+            public void setBigram(final String word0, final String word1, final int frequency) {
+                if (word0.length() < Constants.DICTIONARY_MAX_WORD_LENGTH
+                        && word1.length() < Constants.DICTIONARY_MAX_WORD_LENGTH) {
+                    if (DBG_SAVE_RESTORE) {
+                        Log.d(TAG, "load bigram: " + word0 + "," + word1 + "," + frequency);
+                    }
+                    ++profTotalCount[0];
+                    addBigram(word0, word1, frequency, last);
+                }
+            }
+        };
+
+        // Load the dictionary from binary file
+        final File dictFile = new File(mContext.getFilesDir(), mFileName);
+        final DictDecoder dictDecoder = FormatSpec.getDictDecoder(dictFile,
+                DictDecoder.USE_BYTEARRAY);
+        if (dictDecoder == null) {
+            // This is an expected condition: we don't have a user history dictionary for this
+            // language yet. It will be created sometime later.
+            return;
+        }
+
+        try {
+            dictDecoder.openDictBuffer();
+            UserHistoryDictIOUtils.readDictionaryBinary(dictDecoder, listener);
+        } catch (IOException e) {
+            Log.d(TAG, "IOException on opening a bytebuffer", e);
+        } finally {
+            if (PROFILE_SAVE_RESTORE) {
+                final long diff = System.currentTimeMillis() - now;
+                Log.d(TAG, "PROF: Load UserHistoryDictionary: "
+                        + locale + ", " + diff + "ms. load " + profTotalCount[0] + "entries.");
+            }
+        }
+    }
+
+    protected String getLocale() {
+        return mLocale;
+    }
+
+    public void registerUpdateSession(PersonalizationDictionaryUpdateSession session) {
+        session.setPredictionDictionary(this);
+        mSessions.add(session);
+        session.onDictionaryReady();
+    }
+
+    public void unRegisterUpdateSession(PersonalizationDictionaryUpdateSession session) {
+        mSessions.remove(session);
+    }
+
+    public void clearAndFlushDictionary() {
+        // Clear the node structure on memory
+        clear();
+        // Then flush the cleared state of the dictionary on disk.
+        asyncFlashAllBinaryDictionary();
+    }
+}