Merge "Implement ver4 dictionary GC."

native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.cpp

@@ -94,7 +94,7 @@ bool Ver4BigramListPolicy::addNewEntry(const int terminalId, const int newTarget
 bool Ver4BigramListPolicy::removeEntry(const int terminalId, const int targetTerminalId) {
     const int bigramListPos = mBigramDictContent->getBigramListHeadPos(terminalId);
     if (bigramListPos == NOT_A_DICT_POS) {
-        // Bigram list does't exist.
+        // Bigram list doesn't exist.
         return false;
     }
     const int entryPosToUpdate = getEntryPosToUpdate(targetTerminalId, bigramListPos);
@@ -118,12 +118,62 @@ bool Ver4BigramListPolicy::removeEntry(const int terminalId, const int targetTer
             Ver4DictConstants::NOT_A_TERMINAL_ID /* targetTerminalId */, &writingPos);
 }
 
+bool Ver4BigramListPolicy::updateAllBigramEntriesAndDeleteUselessEntries(const int terminalId,
+        int *const outBigramCount) {
+    const int bigramListPos = mBigramDictContent->getBigramListHeadPos(terminalId);
+    if (bigramListPos == NOT_A_DICT_POS) {
+        // Bigram list doesn't exist.
+        return true;
+    }
+    bool hasNext = true;
+    int readingPos = bigramListPos;
+    while (hasNext) {
+        const int entryPos = readingPos;
+        int probability = NOT_A_PROBABILITY;
+        int targetTerminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
+        mBigramDictContent->getBigramEntryAndAdvancePosition(&probability, &hasNext,
+                &targetTerminalId, &readingPos);
+        if (targetTerminalId == Ver4DictConstants::NOT_A_TERMINAL_ID) {
+            continue;
+        }
+        const int targetPtNodePos = mTerminalPositionLookupTable->getTerminalPtNodePosition(
+                targetTerminalId);
+        if (targetPtNodePos == NOT_A_DICT_POS) {
+            // Invalidate bigram entry.
+            int writingPos = entryPos;
+            return mBigramDictContent->writeBigramEntryAndAdvancePosition(probability, hasNext,
+                    Ver4DictConstants::NOT_A_TERMINAL_ID /* targetTerminalId */, &writingPos);
+        }
+    }
+    return true;
+}
+
+int Ver4BigramListPolicy::getBigramEntryConut(const int terminalId) {
+    const int bigramListPos = mBigramDictContent->getBigramListHeadPos(terminalId);
+    if (bigramListPos == NOT_A_DICT_POS) {
+        // Bigram list doesn't exist.
+        return 0;
+    }
+    int bigramCount = 0;
+    bool hasNext = true;
+    int readingPos = bigramListPos;
+    while (hasNext) {
+        int targetTerminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
+        mBigramDictContent->getBigramEntryAndAdvancePosition(0 /* probability */, &hasNext,
+                &targetTerminalId, &readingPos);
+        if (targetTerminalId != Ver4DictConstants::NOT_A_TERMINAL_ID) {
+            bigramCount++;
+        }
+    }
+    return bigramCount;
+}
+
 int Ver4BigramListPolicy::getEntryPosToUpdate(const int targetTerminalIdToFind,
         const int bigramListPos) const {
     bool hasNext = true;
     int invalidEntryPos = NOT_A_DICT_POS;
     int readingPos = bigramListPos;
-    while(hasNext) {
+    while (hasNext) {
         const int entryPos = readingPos;
         int targetTerminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
         mBigramDictContent->getBigramEntryAndAdvancePosition(0 /* probability */, &hasNext,

native/jni/src/suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.h

@@ -44,6 +44,11 @@ class Ver4BigramListPolicy : public DictionaryBigramsStructurePolicy {
 
     bool removeEntry(const int terminalId, const int targetTerminalId);
 
+    bool updateAllBigramEntriesAndDeleteUselessEntries(const int terminalId,
+            int *const outBigramCount);
+
+    int getBigramEntryConut(const int terminalId);
+
  private:
     DISALLOW_IMPLICIT_CONSTRUCTORS(Ver4BigramListPolicy);
 

native/jni/src/suggest/policyimpl/dictionary/structure/pt_common/pt_node_params.h

@@ -148,6 +148,14 @@ class PtNodeParams {
         return PatriciaTrieReadingUtils::isNotAWord(mFlags);
     }
 
+    AK_FORCE_INLINE bool hasBigrams() const {
+        return PatriciaTrieReadingUtils::hasBigrams(mFlags);
+    }
+
+    AK_FORCE_INLINE bool hasShortcutTargets() const {
+        return PatriciaTrieReadingUtils::hasShortcutTargets(mFlags);
+    }
+
     // Parent node position
     AK_FORCE_INLINE int getParentPos() const {
         return mParentPos;

native/jni/src/suggest/policyimpl/dictionary/structure/v3/dynamic_patricia_trie_gc_event_listeners.cpp

@@ -67,16 +67,13 @@ bool DynamicPatriciaTrieGcEventListeners
 
 bool DynamicPatriciaTrieGcEventListeners::TraversePolicyToUpdateBigramProbability
         ::onVisitingPtNode(const PtNodeParams *const ptNodeParams) {
-    if (!ptNodeParams->isDeleted()) {
+    if (!ptNodeParams->isDeleted() && ptNodeParams->hasBigrams()) {
-        int pos = ptNodeParams->getBigramsPos();
+        int bigramEntryCount = 0;
-        if (pos != NOT_A_DICT_POS) {
+        if (!mPtNodeWriter->updateAllBigramEntriesAndDeleteUselessEntries(ptNodeParams,
-            int bigramEntryCount = 0;
+                &bigramEntryCount)) {
-            if (!mPtNodeWriter->updateAllBigramEntriesAndDeleteUselessEntries(ptNodeParams,
+            return false;
-                    &bigramEntryCount)) {
-                return false;
-            }
-            mValidBigramEntryCount += bigramEntryCount;
         }
+        mValidBigramEntryCount += bigramEntryCount;
     }
     return true;
 }

native/jni/src/suggest/policyimpl/dictionary/structure/v3/dynamic_patricia_trie_updating_helper.cpp

@@ -258,8 +258,7 @@ const PtNodeParams DynamicPatriciaTrieUpdatingHelper::getUpdatedPtNodeParams(
     const PatriciaTrieReadingUtils::NodeFlags flags = PatriciaTrieReadingUtils::createAndGetFlags(
             originalPtNodeParams->isBlacklisted(), originalPtNodeParams->isNotAWord(),
             probability != NOT_A_PROBABILITY /* isTerminal */,
-            originalPtNodeParams->getShortcutPos() != NOT_A_DICT_POS /* hasShortcutTargets */,
+            originalPtNodeParams->hasShortcutTargets(), originalPtNodeParams->hasBigrams(),
-            originalPtNodeParams->getBigramsPos() != NOT_A_DICT_POS /* hasBigrams */,
             codePointCount > 1 /* hasMultipleChars */, CHILDREN_POSITION_FIELD_SIZE);
     return PtNodeParams(originalPtNodeParams, flags, parentPos, codePointCount, codePoints,
             probability);

native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/bigram_dict_content.cpp

@@ -59,7 +59,7 @@ bool BigramDictContent::copyBigramList(const int bigramListPos, const int toPos)
     bool hasNext = true;
     int readingPos = bigramListPos;
     int writingPos = toPos;
-    while(hasNext) {
+    while (hasNext) {
         int probability = NOT_A_PROBABILITY;
         int targetTerminalId = Ver4DictConstants::NOT_A_TERMINAL_ID;
         getBigramEntryAndAdvancePosition(&probability, &hasNext, &targetTerminalId,

native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/probability_dict_content.h

@@ -41,25 +41,29 @@ class ProbabilityDictContent : public SingleDictContent {
     }
 
     bool setProbability(const int terminalId, const int probability) {
-        if (terminalId < 0 || terminalId > getSize()) {
+        if (terminalId < 0) {
             return false;
         }
-        if (terminalId == getSize()) {
+        if (terminalId >= getSize()) {
             // Write new entry.
-            int flagWritingPos = terminalId * (Ver4DictConstants::FLAGS_IN_PROBABILITY_FILE_SIZE
+            int writingPos = getBuffer()->getTailPosition();
-                    + Ver4DictConstants::PROBABILITY_SIZE);
+            while (writingPos <= getEntryPos(terminalId)) {
-            const int dummyFlags = 0;
+                const int dummyFlags = 0;
-            // Write dummy flags.
+                if (!getWritableBuffer()->writeUintAndAdvancePosition(dummyFlags,
-            if (!getWritableBuffer()->writeUintAndAdvancePosition(dummyFlags,
+                        Ver4DictConstants::FLAGS_IN_PROBABILITY_FILE_SIZE, &writingPos)) {
-                    Ver4DictConstants::FLAGS_IN_PROBABILITY_FILE_SIZE, &flagWritingPos)) {
+                    return false;
-                return false;
+                }
+                const int dummyProbability = 0;
+                if (!getWritableBuffer()->writeUintAndAdvancePosition(dummyProbability,
+                        Ver4DictConstants::PROBABILITY_SIZE, &writingPos)) {
+                    return false;
+                }
             }
         }
-        int probabilityWritingPos = terminalId * (Ver4DictConstants::FLAGS_IN_PROBABILITY_FILE_SIZE
+        const int probabilityWritingPos = getEntryPos(terminalId)
-                + Ver4DictConstants::PROBABILITY_SIZE)
+                + Ver4DictConstants::FLAGS_IN_PROBABILITY_FILE_SIZE;
-                        + Ver4DictConstants::FLAGS_IN_PROBABILITY_FILE_SIZE;
+        return getWritableBuffer()->writeUint(probability,
-        return getWritableBuffer()->writeUintAndAdvancePosition(probability,
+                Ver4DictConstants::PROBABILITY_SIZE, probabilityWritingPos);
-                Ver4DictConstants::PROBABILITY_SIZE, &probabilityWritingPos);
     }
 
     bool flushToFile(const char *const dictDirPath) const {
@@ -69,6 +73,11 @@ class ProbabilityDictContent : public SingleDictContent {
  private:
     DISALLOW_COPY_AND_ASSIGN(ProbabilityDictContent);
 
+    int getEntryPos(const int terminalId) const {
+        return terminalId * (Ver4DictConstants::FLAGS_IN_PROBABILITY_FILE_SIZE
+                + Ver4DictConstants::PROBABILITY_SIZE);
+    }
+
     int getSize() const {
         return getBuffer()->getTailPosition() / (Ver4DictConstants::PROBABILITY_SIZE
                 + Ver4DictConstants::FLAGS_IN_PROBABILITY_FILE_SIZE);

native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/sparse_table_dict_content.cpp

@@ -18,6 +18,22 @@
 
 namespace latinime {
 
+bool SparseTableDictContent::copyContent(
+        const SparseTableDictContent *const sparseTableDictContent) {
+    if (!mExpandableLookupTableBuffer.copy(
+            &sparseTableDictContent->mExpandableLookupTableBuffer)) {
+        return false;
+    }
+    if (!mExpandableAddressTableBuffer.copy(
+            &sparseTableDictContent->mExpandableAddressTableBuffer)) {
+        return false;
+    }
+    if (!mExpandableContentBuffer.copy(&sparseTableDictContent->mExpandableContentBuffer)) {
+        return false;
+    }
+    return true;
+}
+
 bool SparseTableDictContent::flush(const char *const dictDirPath,
         const char *const lookupTableFileName, const char *const addressTableFileName,
         const char *const contentFileName) const {

native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/sparse_table_dict_content.h

@@ -75,6 +75,8 @@ class SparseTableDictContent : public DictContent {
                 || mExpandableContentBuffer.isNearSizeLimit();
     }
 
+    bool copyContent(const SparseTableDictContent *const sparseTableDictContent);
+
  protected:
     SparseTable *getUpdatableAddressLookupTable() {
         return &mAddressLookupTable;

native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/terminal_position_lookup_table.h

@@ -44,23 +44,27 @@ class TerminalPositionLookupTable : public SingleDictContent {
         if (terminalId < 0 || terminalId >= mSize) {
             return NOT_A_DICT_POS;
         }
-        const int readingPos = terminalId * Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE;
         return getBuffer()->readUint(Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE,
-                readingPos) - mHeaderRegionSize;
+                getEntryPos(terminalId)) - mHeaderRegionSize;
     }
 
     bool setTerminalPtNodePosition(const int terminalId, const int terminalPtNodePos) {
-        if (terminalId < 0 || terminalId > mSize) {
+        if (terminalId < 0) {
             return NOT_A_DICT_POS;
         }
-        if (terminalId == mSize) {
+        if (terminalId >= mSize) {
-            // Use new terminal id.
+            int writingPos = getBuffer()->getTailPosition();
-            mSize += 1;
+            while(writingPos <= getEntryPos(terminalId)) {
+                // Write new entry.
+                getWritableBuffer()->writeUintAndAdvancePosition(
+                        Ver4DictConstants::NOT_A_TERMINAL_ADDRESS,
+                        Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE, &writingPos);
+            }
+            mSize = getBuffer()->getTailPosition()
+                    / Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE;
         }
-        int writingPos = terminalId * Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE;
+        return getWritableBuffer()->writeUint(terminalPtNodePos + mHeaderRegionSize,
-        return getWritableBuffer()->writeUintAndAdvancePosition(
+                Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE, getEntryPos(terminalId));
-                terminalPtNodePos + mHeaderRegionSize,
-                Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE, &writingPos);
     }
 
     int getNextTerminalId() const {
@@ -94,6 +98,10 @@ class TerminalPositionLookupTable : public SingleDictContent {
  private:
     DISALLOW_COPY_AND_ASSIGN(TerminalPositionLookupTable);
 
+    int getEntryPos(const int terminalId) const {
+        return terminalId * Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE;
+    }
+
     int mSize;
     const int mHeaderRegionSize;
 };

native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.h

@@ -93,6 +93,10 @@ class Ver4DictBuffers {
         return &mBigramDictContent;
     }
 
+    AK_FORCE_INLINE ShortcutDictContent *getUpdatableShortcutDictContent() {
+        return &mShortcutDictContent;
+    }
+
     AK_FORCE_INLINE const ShortcutDictContent *getShortcutDictContent() const {
         return &mShortcutDictContent;
     }

native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.cpp

@@ -41,6 +41,7 @@ const int Ver4DictConstants::NOT_A_TERMINAL_ID = -1;
 const int Ver4DictConstants::PROBABILITY_SIZE = 1;
 const int Ver4DictConstants::FLAGS_IN_PROBABILITY_FILE_SIZE = 1;
 const int Ver4DictConstants::TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE = 3;
+const int Ver4DictConstants::NOT_A_TERMINAL_ADDRESS = 0;
 const int Ver4DictConstants::TERMINAL_ID_FIELD_SIZE = 4;
 
 const int Ver4DictConstants::BIGRAM_ADDRESS_TABLE_BLOCK_SIZE = 4;

native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.h

@@ -41,6 +41,7 @@ class Ver4DictConstants {
     static const int PROBABILITY_SIZE;
     static const int FLAGS_IN_PROBABILITY_FILE_SIZE;
     static const int TERMINAL_ADDRESS_TABLE_ADDRESS_SIZE;
+    static const int NOT_A_TERMINAL_ADDRESS;
     static const int TERMINAL_ID_FIELD_SIZE;
 
     static const int BIGRAM_ADDRESS_TABLE_BLOCK_SIZE;

native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_node_writer.cpp

@@ -45,8 +45,17 @@ bool Ver4PatriciaTrieNodeWriter::markPtNodeAsDeleted(
                     true /* isDeleted */);
     int writingPos = toBeUpdatedPtNodeParams->getHeadPos();
     // Update flags.
-    return DynamicPatriciaTrieWritingUtils::writeFlagsAndAdvancePosition(mTrieBuffer, updatedFlags,
+    if (!DynamicPatriciaTrieWritingUtils::writeFlagsAndAdvancePosition(mTrieBuffer, updatedFlags,
-            &writingPos);
+            &writingPos)) {
+        return false;
+    }
+    if (toBeUpdatedPtNodeParams->getTerminalId() != NOT_A_DICT_POS) {
+        // The PtNode is a terminal. Delete entry from the terminal position lookup table.
+        return mBuffers->getUpdatableTerminalPositionLookupTable()->setTerminalPtNodePosition(
+                toBeUpdatedPtNodeParams->getTerminalId(), NOT_A_DICT_POS /* ptNodePos */);
+    } else {
+        return true;
+    }
 }
 
 bool Ver4PatriciaTrieNodeWriter::markPtNodeAsMoved(
@@ -171,7 +180,7 @@ bool Ver4PatriciaTrieNodeWriter::writePtNodeAndAdvancePosition(
     PatriciaTrieReadingUtils::NodeFlags nodeFlags =
             PatriciaTrieReadingUtils::createAndGetFlags(ptNodeParams->isBlacklisted(),
                     ptNodeParams->isNotAWord(), isTerminal,
-                    false /* hasShortcutTargets */, false /* hasBigrams */,
+                    ptNodeParams->hasShortcutTargets(), ptNodeParams->hasBigrams(),
                     ptNodeParams->getCodePointCount() > 1 /* hasMultipleChars */,
                     CHILDREN_POSITION_FIELD_SIZE);
     int flagsFieldPos = nodePos;
@@ -198,16 +207,49 @@ bool Ver4PatriciaTrieNodeWriter::removeBigramEntry(
 
 bool Ver4PatriciaTrieNodeWriter::updateAllBigramEntriesAndDeleteUselessEntries(
             const PtNodeParams *const sourcePtNodeParams, int *const outBigramEntryCount) {
-    // TODO: Implement.
+    return mBigramPolicy->updateAllBigramEntriesAndDeleteUselessEntries(
-    return false;
+            sourcePtNodeParams->getTerminalId(), outBigramEntryCount);
 }
 
 bool Ver4PatriciaTrieNodeWriter::updateAllPositionFields(
         const PtNodeParams *const toBeUpdatedPtNodeParams,
         const DictPositionRelocationMap *const dictPositionRelocationMap,
         int *const outBigramEntryCount) {
-    // TODO: Implement.
+    int parentPos = toBeUpdatedPtNodeParams->getParentPos();
-    return false;
+    if (parentPos != NOT_A_DICT_POS) {
+        PtNodeWriter::PtNodePositionRelocationMap::const_iterator it =
+                dictPositionRelocationMap->mPtNodePositionRelocationMap.find(parentPos);
+        if (it != dictPositionRelocationMap->mPtNodePositionRelocationMap.end()) {
+            parentPos = it->second;
+        }
+    }
+    int writingPos = toBeUpdatedPtNodeParams->getHeadPos()
+            + DynamicPatriciaTrieWritingUtils::NODE_FLAG_FIELD_SIZE;
+    // Write updated parent offset.
+    if (!DynamicPatriciaTrieWritingUtils::writeParentPosOffsetAndAdvancePosition(mTrieBuffer,
+            parentPos, toBeUpdatedPtNodeParams->getHeadPos(), &writingPos)) {
+        return false;
+    }
+
+    // Updates children position.
+    int childrenPos = toBeUpdatedPtNodeParams->getChildrenPos();
+    if (childrenPos != NOT_A_DICT_POS) {
+        PtNodeWriter::PtNodeArrayPositionRelocationMap::const_iterator it =
+                dictPositionRelocationMap->mPtNodeArrayPositionRelocationMap.find(childrenPos);
+        if (it != dictPositionRelocationMap->mPtNodeArrayPositionRelocationMap.end()) {
+            childrenPos = it->second;
+        }
+    }
+    if (!updateChildrenPosition(toBeUpdatedPtNodeParams, childrenPos)) {
+        return false;
+    }
+
+    // Counts bigram entries.
+    if (outBigramEntryCount) {
+        *outBigramEntryCount = mBigramPolicy->getBigramEntryConut(
+                toBeUpdatedPtNodeParams->getTerminalId());
+    }
+    return true;
 }
 
 }

native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp

@@ -223,7 +223,15 @@ void Ver4PatriciaTriePolicy::flush(const char *const filePath) {
 }
 
 void Ver4PatriciaTriePolicy::flushWithGC(const char *const filePath) {
-    // TODO: Implement.
+    if (!mBuffers.get()->isUpdatable()) {
+        AKLOGI("Warning: flushWithGC() is called for non-updatable dictionary.");
+        return;
+    }
+    const bool needsToDecay = mHeaderPolicy.isDecayingDict()
+            && (mNeedsToDecayForTesting || ForgettingCurveUtils::needsToDecay(
+                    false /* mindsBlockByDecay */, mUnigramCount, mBigramCount, &mHeaderPolicy));
+    mWritingHelper.writeToDictFileWithGC(getRootPosition(), filePath, &mHeaderPolicy, needsToDecay);
+    mNeedsToDecayForTesting = false;
 }
 
 bool Ver4PatriciaTriePolicy::needsToRunGC(const bool mindsBlockByGC) const {

native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_writing_helper.cpp

@@ -20,6 +20,7 @@
 
 #include "suggest/policyimpl/dictionary/bigram/ver4_bigram_list_policy.h"
 #include "suggest/policyimpl/dictionary/header/header_policy.h"
+#include "suggest/policyimpl/dictionary/structure/v3/dynamic_patricia_trie_gc_event_listeners.h"
 #include "suggest/policyimpl/dictionary/shortcut/ver4_shortcut_list_policy.h"
 #include "suggest/policyimpl/dictionary/structure/v4/ver4_dict_buffers.h"
 #include "suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.h"
@@ -91,7 +92,78 @@ bool Ver4PatriciaTrieWritingHelper::runGC(const int rootPtNodeArrayPos,
 
     DynamicPatriciaTrieReadingHelper readingHelper(mBuffers->getTrieBuffer(), &ptNodeReader);
     readingHelper.initWithPtNodeArrayPos(rootPtNodeArrayPos);
+    DynamicPatriciaTrieGcEventListeners
+            ::TraversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted
+                    traversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted(
+                            headerPolicy, &ptNodeWriter, mBuffers->getWritableTrieBuffer(),
+                            needsToDecay);
+    if (!readingHelper.traverseAllPtNodesInPostorderDepthFirstManner(
+            &traversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted)) {
+        return false;
+    }
+    if (needsToDecay && traversePolicyToUpdateUnigramProbabilityAndMarkUselessPtNodesAsDeleted
+            .getValidUnigramCount() > ForgettingCurveUtils::MAX_UNIGRAM_COUNT_AFTER_GC) {
+        // TODO: Remove more unigrams.
+    }
 
+    readingHelper.initWithPtNodeArrayPos(rootPtNodeArrayPos);
+    DynamicPatriciaTrieGcEventListeners::TraversePolicyToUpdateBigramProbability
+            traversePolicyToUpdateBigramProbability(&ptNodeWriter);
+    if (!readingHelper.traverseAllPtNodesInPostorderDepthFirstManner(
+            &traversePolicyToUpdateBigramProbability)) {
+        return false;
+    }
+    if (needsToDecay && traversePolicyToUpdateBigramProbability.getValidBigramEntryCount()
+            > ForgettingCurveUtils::MAX_BIGRAM_COUNT_AFTER_GC) {
+        // TODO: Remove more bigrams.
+    }
+
+    // Mapping from positions in mBuffer to positions in bufferToWrite.
+    PtNodeWriter::DictPositionRelocationMap dictPositionRelocationMap;
+    readingHelper.initWithPtNodeArrayPos(rootPtNodeArrayPos);
+    Ver4PatriciaTrieNodeWriter ptNodeWriterForNewBuffers(buffersToWrite->getWritableTrieBuffer(),
+            buffersToWrite, &ptNodeReader, &bigramPolicy, &shortcutPolicy);
+    DynamicPatriciaTrieGcEventListeners::TraversePolicyToPlaceAndWriteValidPtNodesToBuffer
+            traversePolicyToPlaceAndWriteValidPtNodesToBuffer(&ptNodeWriterForNewBuffers,
+                    buffersToWrite->getWritableTrieBuffer(), &dictPositionRelocationMap);
+    if (!readingHelper.traverseAllPtNodesInPtNodeArrayLevelPreorderDepthFirstManner(
+            &traversePolicyToPlaceAndWriteValidPtNodesToBuffer)) {
+        return false;
+    }
+
+    // Create policy instances for the GCed dictionary.
+    Ver4PatriciaTrieNodeReader newPtNodeReader(buffersToWrite->getTrieBuffer(),
+            buffersToWrite->getProbabilityDictContent());
+    Ver4BigramListPolicy newBigramPolicy(buffersToWrite->getUpdatableBigramDictContent(),
+            buffersToWrite->getTerminalPositionLookupTable());
+    Ver4ShortcutListPolicy newShortcutPolicy(buffersToWrite->getShortcutDictContent(),
+            buffersToWrite->getTerminalPositionLookupTable());
+    Ver4PatriciaTrieNodeWriter newPtNodeWriter(buffersToWrite->getWritableTrieBuffer(),
+            buffersToWrite, &newPtNodeReader, &newBigramPolicy, &newShortcutPolicy);
+
+    if(!buffersToWrite->getUpdatableBigramDictContent()->copyContent(
+            mBuffers->getBigramDictContent())) {
+        return false;
+    }
+    if(!buffersToWrite->getUpdatableShortcutDictContent()->copyContent(
+            mBuffers->getShortcutDictContent())) {
+        return false;
+    }
+
+    DynamicPatriciaTrieReadingHelper newDictReadingHelper(buffersToWrite->getTrieBuffer(),
+            &newPtNodeReader);
+    newDictReadingHelper.initWithPtNodeArrayPos(rootPtNodeArrayPos);
+    DynamicPatriciaTrieGcEventListeners::TraversePolicyToUpdateAllPositionFields
+            traversePolicyToUpdateAllPositionFields(&newPtNodeWriter, &dictPositionRelocationMap);
+    if (!newDictReadingHelper.traverseAllPtNodesInPtNodeArrayLevelPreorderDepthFirstManner(
+            &traversePolicyToUpdateAllPositionFields)) {
+        return false;
+    }
+
+    // TODO: GC for dict contents.
+
+    *outUnigramCount = traversePolicyToUpdateAllPositionFields.getUnigramCount();
+    *outBigramCount = traversePolicyToUpdateAllPositionFields.getBigramCount();
     return true;
 }
 

native/jni/src/suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.cpp

@@ -131,4 +131,21 @@ bool BufferWithExtendableBuffer::checkAndPrepareWriting(const int pos, const int
     return true;
 }
 
+bool BufferWithExtendableBuffer::copy(const BufferWithExtendableBuffer *const sourceBuffer) {
+    int copyingPos = 0;
+    const int tailPos = sourceBuffer->getTailPosition();
+    const int maxDataChunkSize = sizeof(uint32_t);
+    while (copyingPos < tailPos) {
+        const int remainingSize = tailPos - copyingPos;
+        const int copyingSize = (remainingSize >= maxDataChunkSize) ?
+                maxDataChunkSize : remainingSize;
+        const uint32_t data = sourceBuffer->readUint(copyingSize, copyingPos);
+        if (!writeUint(data, copyingSize, copyingPos)) {
+            return false;
+        }
+        copyingPos += copyingSize;
+    }
+    return true;
+}
+
 }

native/jni/src/suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h

@@ -100,6 +100,8 @@ class BufferWithExtendableBuffer {
     bool writeCodePointsAndAdvancePosition(const int *const codePoints, const int codePointCount,
             const bool writesTerminator, int *const pos);
 
+    bool copy(const BufferWithExtendableBuffer *const sourceBuffer);
+
  private:
     DISALLOW_COPY_AND_ASSIGN(BufferWithExtendableBuffer);
 

tests/src/com/android/inputmethod/latin/Ver4BinaryDictionaryTests.java

@@ -297,4 +297,46 @@ public class Ver4BinaryDictionaryTests extends AndroidTestCase {
         binaryDictionary.close();
     }
 
+    public void testFlushWithGCDictionary() {
+        final String dictVersion = Long.toString(System.currentTimeMillis());
+        File trieFile = null;
+        try {
+            trieFile = createEmptyDictionaryAndGetTrieFile(dictVersion);
+        } catch (IOException e) {
+            fail("IOException while writing an initial dictionary : " + e);
+        }
+        BinaryDictionary binaryDictionary = new BinaryDictionary(trieFile.getAbsolutePath(),
+                0 /* offset */, trieFile.length(), true /* useFullEditDistance */,
+                Locale.getDefault(), TEST_LOCALE, true /* isUpdatable */);
+
+        final int unigramProbability = 100;
+        final int bigramProbability = 10;
+        binaryDictionary.addUnigramWord("aaa", unigramProbability);
+        binaryDictionary.addUnigramWord("abb", unigramProbability);
+        binaryDictionary.addUnigramWord("bcc", unigramProbability);
+        binaryDictionary.addBigramWords("aaa", "abb", bigramProbability);
+        binaryDictionary.addBigramWords("aaa", "bcc", bigramProbability);
+        binaryDictionary.addBigramWords("abb", "aaa", bigramProbability);
+        binaryDictionary.addBigramWords("abb", "bcc", bigramProbability);
+        binaryDictionary.flushWithGC();
+        binaryDictionary.close();
+
+        binaryDictionary = new BinaryDictionary(trieFile.getAbsolutePath(),
+                0 /* offset */, trieFile.length(), true /* useFullEditDistance */,
+                Locale.getDefault(), TEST_LOCALE, true /* isUpdatable */);
+        final int probability = binaryDictionary.calculateProbability(unigramProbability,
+                bigramProbability);
+        assertEquals(unigramProbability, binaryDictionary.getFrequency("aaa"));
+        assertEquals(unigramProbability, binaryDictionary.getFrequency("abb"));
+        assertEquals(unigramProbability, binaryDictionary.getFrequency("bcc"));
+        assertEquals(probability, binaryDictionary.getBigramProbability("aaa", "abb"));
+        assertEquals(probability, binaryDictionary.getBigramProbability("aaa", "bcc"));
+        assertEquals(probability, binaryDictionary.getBigramProbability("abb", "aaa"));
+        assertEquals(probability, binaryDictionary.getBigramProbability("abb", "bcc"));
+        assertEquals(false, binaryDictionary.isValidBigram("bcc", "aaa"));
+        assertEquals(false, binaryDictionary.isValidBigram("bcc", "bbc"));
+        assertEquals(false, binaryDictionary.isValidBigram("aaa", "aaa"));
+        binaryDictionary.flushWithGC();
+        binaryDictionary.close();
+    }
 }