- Avoid explicit Close() when not necessary. Destructor does the necessary.

- Check Close() and Sync() results.
- GC unused code.

14 files changed, 36 insertions, 300 deletions

diff --git a/searchlib/src/vespa/searchlib/attribute/attributefilewriter.cpp b/searchlib/src/vespa/searchlib/attribute/attributefilewriter.cpp
index 30f417c7532..91eb229b271 100644
--- a/searchlib/src/vespa/searchlib/attribute/attributefilewriter.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/attributefilewriter.cpp
@@ -48,8 +48,8 @@ updateHeader(const vespalib::string &name, uint64_t fileBitSize)
     h.putTag(Tag("frozen", 1));
     h.putTag(Tag("fileBitSize", fileBitSize));
     h.rewriteFile(f);
-    f.Sync();
-    f.Close();
+    bool sync_ok = f.Sync();
+    assert(sync_ok);
 }
 
 /*
diff --git a/searchlib/src/vespa/searchlib/attribute/sourceselector.cpp b/searchlib/src/vespa/searchlib/attribute/sourceselector.cpp
index b46866e61e2..3bc85783c2f 100644
--- a/searchlib/src/vespa/searchlib/attribute/sourceselector.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/sourceselector.cpp
@@ -95,7 +95,6 @@ SourceSelector::LoadInfo::load()
     if (fileHeader.hasTag(docIdLimitTag)) {
         _header._docIdLimit = fileHeader.getTag(docIdLimitTag).asInteger();
     }
-    file.Close();
 }
 
 SourceSelector::SourceSelector(Source defaultSource, AttributeVector::SP realSource) :
@@ -106,14 +105,14 @@ SourceSelector::SourceSelector(Source defaultSource, AttributeVector::SP realSou
 SourceSelector::SaveInfo::UP
 SourceSelector::extractSaveInfo(const vespalib::string & baseFileName)
 {
-    return SaveInfo::UP(new SaveInfo(baseFileName, getDefaultSource(), getBaseId(),
-                                     getDocIdLimit(), *_realSource));
+    return std::make_unique<SaveInfo>(baseFileName, getDefaultSource(), getBaseId(),
+                                      getDocIdLimit(), *_realSource);
 }
 
 SourceSelector::LoadInfo::UP
 SourceSelector::extractLoadInfo(const vespalib::string & baseFileName)
 {
-    return LoadInfo::UP(new LoadInfo(baseFileName));
+    return std::make_unique<LoadInfo>(baseFileName);
 }
 
 SourceSelector::Histogram SourceSelector::getDistribution() const
diff --git a/searchlib/src/vespa/searchlib/common/documentsummary.cpp b/searchlib/src/vespa/searchlib/common/documentsummary.cpp
index 8e70ffa7844..55ecc558598 100644
--- a/searchlib/src/vespa/searchlib/common/documentsummary.cpp
+++ b/searchlib/src/vespa/searchlib/common/documentsummary.cpp
@@ -33,7 +33,6 @@ DocumentSummary::readDocIdLimit(const vespalib::string &dir, uint32_t &count)
     p = qcntfile.ReadLine(numbuf, sizeof(numbuf));
     while (*p >= '0' && *p <= '9')
         qcnt = qcnt * 10 + *p++ - '0';
-    qcntfile.Close();
     count = qcnt;
     return true;
 }
@@ -52,8 +51,14 @@ DocumentSummary::writeDocIdLimit(const vespalib::string &dir, uint32_t count)
     }
     qcntfile.addNum(count, 0, ' ');
     qcntfile.WriteByte('\n');
-    qcntfile.Sync();
-    qcntfile.Close();
+    if ( ! qcntfile.Sync() ) {
+        LOG(error, "Could not sync %s: %s", qcntname.c_str(), getLastErrorString().c_str());
+        return false;
+    }
+    if ( ! qcntfile.Close() ) {
+        LOG(error, "Could not sync %s: %s", qcntname.c_str(), getLastErrorString().c_str());
+        return false;
+    }
     return true;
 }
 
diff --git a/searchlib/src/vespa/searchlib/diskindex/bitvectorfile.cpp b/searchlib/src/vespa/searchlib/diskindex/bitvectorfile.cpp
index 65ce5decc50..d2b02b02a87 100644
--- a/searchlib/src/vespa/searchlib/diskindex/bitvectorfile.cpp
+++ b/searchlib/src/vespa/searchlib/diskindex/bitvectorfile.cpp
@@ -23,7 +23,6 @@ readHeader(vespalib::FileHeader &h,
     Fast_BufferedFile file(32_Ki);
     file.OpenReadOnly(name.c_str());
     h.readFile(file);
-    file.Close();
 }
 
 }
diff --git a/searchlib/src/vespa/searchlib/diskindex/bitvectoridxfile.cpp b/searchlib/src/vespa/searchlib/diskindex/bitvectoridxfile.cpp
index f85c6c20624..17ad4c5b846 100644
--- a/searchlib/src/vespa/searchlib/diskindex/bitvectoridxfile.cpp
+++ b/searchlib/src/vespa/searchlib/diskindex/bitvectoridxfile.cpp
@@ -22,7 +22,6 @@ readHeader(vespalib::FileHeader &h, const vespalib::string &name)
     Fast_BufferedFile file(32_Ki);
     file.OpenReadOnly(name.c_str());
     h.readFile(file);
-    file.Close();
 }
 
 }
diff --git a/searchlib/src/vespa/searchlib/diskindex/pagedict4file.cpp b/searchlib/src/vespa/searchlib/diskindex/pagedict4file.cpp
index 96649d27b82..b845d21d027 100644
--- a/searchlib/src/vespa/searchlib/diskindex/pagedict4file.cpp
+++ b/searchlib/src/vespa/searchlib/diskindex/pagedict4file.cpp
@@ -15,7 +15,6 @@ namespace {
 vespalib::string myPId("PageDict4P.1");
 vespalib::string mySPId("PageDict4SP.1");
 vespalib::string mySSId("PageDict4SS.1");
-vespalib::string emptyId;
 
 void assertOpenWriteOnly(bool ok, const vespalib::string &fileName)
 {
@@ -265,10 +264,7 @@ PageDict4FileSeqRead::close()
     _ssReadContext.setFile(nullptr);
     _spReadContext.setFile(nullptr);
     _pReadContext.setFile(nullptr);
-    _ssfile.Close();
-    _spfile.Close();
-    _pfile.Close();
-    return true;
+    return _ssfile.Close() && _spfile.Close() &&_pfile.Close();
 }
 
 
diff --git a/searchlib/src/vespa/searchlib/diskindex/wordnummapper.cpp b/searchlib/src/vespa/searchlib/diskindex/wordnummapper.cpp
index 49e175ba102..cd9cd6c34da 100644
--- a/searchlib/src/vespa/searchlib/diskindex/wordnummapper.cpp
+++ b/searchlib/src/vespa/searchlib/diskindex/wordnummapper.cpp
@@ -2,7 +2,6 @@
 
 #include "wordnummapper.h"
 #include <vespa/fastlib/io/bufferedfile.h>
-#include <cassert>
 
 namespace search::diskindex {
 
@@ -33,7 +32,6 @@ WordNumMapping::readMappingFile(const vespalib::string &name,
 
     old2newwordfile.Read(&map[1],
                          static_cast<size_t>(tempfilesize));
-    old2newwordfile.Close();
     map[0] = noWordNum();
     map[tempfileentries + 1] = noWordNumHigh();
 }
diff --git a/searchlib/src/vespa/searchlib/diskindex/zcposting.cpp b/searchlib/src/vespa/searchlib/diskindex/zcposting.cpp
index 4441b868b15..544e8d9f262 100644
--- a/searchlib/src/vespa/searchlib/diskindex/zcposting.cpp
+++ b/searchlib/src/vespa/searchlib/diskindex/zcposting.cpp
@@ -15,7 +15,6 @@ namespace {
 
 vespalib::string myId5("Zc.5");
 vespalib::string myId4("Zc.4");
-vespalib::string emptyId;
 vespalib::string interleaved_features("interleaved_features");
 
 }
@@ -98,9 +97,8 @@ Zc4PostingSeqRead::close()
 {
     auto &readContext = _reader.get_read_context();
     readContext.dropComprBuf();
-    _file.Close();
     readContext.setFile(nullptr);
-    return true;
+    return _file.Close();
 }
 
 
diff --git a/searchlib/src/vespa/searchlib/docstore/filechunk.cpp b/searchlib/src/vespa/searchlib/docstore/filechunk.cpp
index b7b72552914..278fe166272 100644
--- a/searchlib/src/vespa/searchlib/docstore/filechunk.cpp
+++ b/searchlib/src/vespa/searchlib/docstore/filechunk.cpp
@@ -101,7 +101,6 @@ FileChunk::FileChunk(FileId fileId, NameId nameId, const vespalib::string & base
             _diskFootprint += idxFile.GetSize();
             _modificationTime = FileKit::getModificationTime(_idxFileName);
         } else {
-            dataFile.Close();
             throw SummaryException("Failed opening idx file", idxFile, VESPA_STRLOC);
         }
     }
diff --git a/searchlib/src/vespa/searchlib/transactionlog/domainpart.cpp b/searchlib/src/vespa/searchlib/transactionlog/domainpart.cpp
index 2ca2f15545d..3a24d348676 100644
--- a/searchlib/src/vespa/searchlib/transactionlog/domainpart.cpp
+++ b/searchlib/src/vespa/searchlib/transactionlog/domainpart.cpp
@@ -124,7 +124,9 @@ handleReadError(const char *text, FastOS_FileInterface &file, ssize_t len, ssize
         e += fmt(" Truncate to %" PRId64 " and continue", lastKnownGoodPos);
         LOG(error, "%s", e.c_str());
         FastOS_File truncateFile(file.GetFileName());
-        file.Close();
+        if ( ! file.Close()) {
+            e += getError(file);
+        }
         if ( truncateFile.OpenWriteOnlyExisting()) {
             if (truncateFile.SetSize(lastKnownGoodPos)) {
                 if (truncateFile.Close()) {
@@ -243,7 +245,6 @@ DomainPart::buildPacketMapping(bool allowTruncate)
         }
         currPos = transLog.GetPosition();
     }
-    transLog.Close();
     return currPos;
 }
 
diff --git a/searchlib/src/vespa/searchlib/util/fileutil.cpp b/searchlib/src/vespa/searchlib/util/fileutil.cpp
index 5c213d4e0f0..83f3fe3a5fa 100644
--- a/searchlib/src/vespa/searchlib/util/fileutil.cpp
+++ b/searchlib/src/vespa/searchlib/util/fileutil.cpp
@@ -4,7 +4,6 @@
 #include "filesizecalculator.h"
 #include <vespa/vespalib/util/exceptions.h>
 #include <vespa/vespalib/util/guard.h>
-#include <cassert>
 #include <fcntl.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
@@ -19,12 +18,11 @@ using vespalib::GenericHeader;
 using vespalib::FileDescriptor;
 using vespalib::getLastErrorString;
 
-namespace search {
-namespace fileutil {
+namespace search::fileutil {
 
 LoadedMmap::LoadedMmap(const vespalib::string &fileName)
-    : LoadedBuffer(NULL, 0),
-      _mapBuffer(NULL),
+    : LoadedBuffer(nullptr, 0),
+      _mapBuffer(nullptr),
       _mapSize(0)
 {
     FileDescriptor fd(open(fileName.c_str(), O_RDONLY, 0664));
@@ -35,7 +33,7 @@ LoadedMmap::LoadedMmap(const vespalib::string &fileName)
             uint64_t fileSize = stbuf.st_size;
             size_t sz = fileSize;
             if (sz) {
-                void *tmpBuffer = mmap(NULL, sz, PROT_READ, MAP_PRIVATE, fd.fd(), 0);
+                void *tmpBuffer = mmap(nullptr, sz, PROT_READ, MAP_PRIVATE, fd.fd(), 0);
                 if (tmpBuffer != MAP_FAILED) {
                     _mapSize = sz;
                     _mapBuffer = tmpBuffer;
@@ -78,14 +76,15 @@ LoadedMmap::~LoadedMmap() {
 
 }
 
+namespace search {
+
 std::unique_ptr<FastOS_FileInterface>
 FileUtil::openFile(const vespalib::string &fileName)
 {
-    std::unique_ptr<Fast_BufferedFile> file(new Fast_BufferedFile());
+    auto file = std::make_unique<Fast_BufferedFile>();
     file->EnableDirectIO();
     if (!file->OpenReadOnly(fileName.c_str())) {
         LOG(error, "could not open %s: %s", file->GetFileName(), getLastErrorString().c_str());
-        file->Close();
         throw IllegalStateException(make_string("Failed opening '%s' for direct IO reading.", file->GetFileName()));
     }
     return file;
@@ -97,12 +96,11 @@ using fileutil::LoadedMmap;
 LoadedBuffer::UP
 FileUtil::loadFile(const vespalib::string &fileName)
 {
-    LoadedBuffer::UP data(new LoadedMmap(fileName));
+    auto data = std::make_unique<LoadedMmap>(fileName);
     FastOS_File file(fileName.c_str());
     if (!file.OpenReadOnly()) {
         LOG(error, "could not open %s: %s", file.GetFileName(), getLastErrorString().c_str());
     }
-    file.Close();
     return data;
 }
 
@@ -125,44 +123,6 @@ void FileWriterBase::handleError(ssize_t numRead, size_t wanted)
     }
 }
 
-SequentialFileArray::SequentialFileArray(const vespalib::string & fname) :
-    _backingFile(),
-    _name(fname)
-{
-    _backingFile->EnableDirectIO();
-}
-
-SequentialFileArray::~SequentialFileArray()
-{
-    close();
-}
-
-void SequentialFileArray::rewind()
-{
-    assert(_backingFile->SetPosition(0));
-}
-
-void SequentialFileArray::close()
-{
-    _backingFile->Close();
-}
-
-void SequentialFileArray::erase()
-{
-    close();
-    FastOS_File::Delete(_backingFile->GetFileName());
-}
-
-void SequentialFileArray::openReadOnly()
-{
-    _backingFile->ReadOpen(_name.c_str());
-}
-
-void SequentialFileArray::openWriteOnly()
-{
-    _backingFile->OpenWriteOnlyTruncate(_name.c_str());
-}
-
 ssize_t
 FileReaderBase::read(void *buf, size_t sz) {
     ssize_t numRead = _file.Read(buf, sz);
diff --git a/searchlib/src/vespa/searchlib/util/fileutil.h b/searchlib/src/vespa/searchlib/util/fileutil.h
index 27761403b96..74096d8b5dd 100644
--- a/searchlib/src/vespa/searchlib/util/fileutil.h
+++ b/searchlib/src/vespa/searchlib/util/fileutil.h
@@ -104,67 +104,6 @@ public:
     }
 };
 
-class SequentialFileArray
-{
-public:
-    SequentialFileArray(const vespalib::string & fname);
-    virtual ~SequentialFileArray();
-    const vespalib::string & getName() const { return _name; }
-    void rewind();
-    void close();
-    void erase();
-protected:
-    void openReadOnly();
-    void openWriteOnly();
-    std::unique_ptr<Fast_BufferedFile> _backingFile;
-    vespalib::string _name;
-};
-
-template <typename T>
-class SequentialFileArrayRead : public SequentialFileArray
-{
-public:
-    SequentialFileArrayRead(const vespalib::string & fname);
-    ~SequentialFileArrayRead();
-    T getNext() const { return _fileReader.readHostOrder(); }
-    bool hasNext() const;
-    size_t size() const;
-private:
-    mutable FileReader<T> _fileReader;
-};
-
-template <typename T>
-class SequentialFileArrayWrite : public SequentialFileArray
-{
-public:
-    SequentialFileArrayWrite(const vespalib::string & fname);
-    void push_back(const T & v) { _count++; _fileWriter.write(&v, sizeof(v)); }
-    size_t size() const { return _count; }
-    bool empty() const { return _count == 0; }
-private:
-    size_t _count;
-    FileWriterBase    _fileWriter;
-};
-
-template <typename T, typename S>
-class MergeSorter
-{
-public:
-    MergeSorter(const vespalib::string & name, size_t chunkSize);
-    void push_back(const T & v);
-    void commit() { sortChunk(); merge(); }
-    const vespalib::string & getName() const { return _name; }
-    void rewind() { }
-private:
-    vespalib::string genName(size_t n);
-    void merge();
-    void sortChunk();
-
-    std::vector<T> _chunk;
-    size_t _chunkCount;
-    vespalib::string _name;
-};
-
 template <typename T>
 class SequentialReadModifyWriteInterface
 {
@@ -199,32 +138,5 @@ private:
     size_t _wp;
 };
 
-template <typename T, typename R, typename W>
-class SequentialReaderWriter : public SequentialReadModifyWriteInterface<T>
-{
-public:
-    SequentialReaderWriter(R & reader, W & writer);
-    ~SequentialReaderWriter();
-    virtual const T & read()        { return _lastRead; }
-    virtual void write(const T & v) { _writer.push_back(v); }
-    virtual bool next() {
-        bool hasMore(_reader.hasNext());
-        if (hasMore) {
-            _lastRead = _reader.getNext();
-        }
-        return hasMore;
-    }
-    virtual size_t size()     const { return _reader.size(); }
-    virtual void rewind() {
-        _reader.rewind();
-        next();
-        _writer.rewind();
-    }
-private:
-    T   _lastRead;
-    R & _reader;
-    W & _writer;
-};
-
 }
 
diff --git a/searchlib/src/vespa/searchlib/util/fileutil.hpp b/searchlib/src/vespa/searchlib/util/fileutil.hpp
index eb0d62b195e..98e54581ac7 100644
--- a/searchlib/src/vespa/searchlib/util/fileutil.hpp
+++ b/searchlib/src/vespa/searchlib/util/fileutil.hpp
@@ -7,122 +7,6 @@
 namespace search {
 
 template <typename T>
-SequentialFileArrayRead<T>::SequentialFileArrayRead(const vespalib::string & fname) :
-    SequentialFileArray(fname),
-    _fileReader(std::make_unique<Fast_BufferedFile>(_backingFile))
-{
-    openReadOnly();
-}
-
-template <typename T>
-bool
-SequentialFileArrayRead<T>::hasNext() const {
-    return _backingFile->BytesLeft() >= sizeof(T);
-
-}
-
-template <typename T>
-size_t SequentialFileArrayRead<T>::size() const
-{
-    return _backingFile->GetSize()/sizeof(T);
-}
-
-template <typename T>
-SequentialFileArrayWrite<T>::SequentialFileArrayWrite(const vespalib::string & fname) :
-    SequentialFileArray(fname),
-    _count(0),
-    _fileWriter(_backingFile)
-{
-    openWriteOnly();
-}
-
-template <typename T, typename S>
-MergeSorter<T, S>::MergeSorter(const vespalib::string & name, size_t chunkSize) :
-    _chunk(),
-    _chunkCount(0),
-    _name(name + ".sorted")
-{
-    _chunk.reserve(chunkSize);
-}
-
-template <typename T, typename S>
-void MergeSorter<T, S>::push_back(const T & v)
-{
-    if (_chunk.size() < _chunk.capacity()) {
-        _chunk.push_back(v);
-        if (_chunk.size() == _chunk.capacity()) {
-            sortChunk();
-        }
-    }
-}
-
-template <typename T, typename S>
-vespalib::string MergeSorter<T, S>::genName(size_t n)
-{
-    char tmp[32];
-    sprintf(tmp, ".%zd", n);
-    vespalib::string fname(_name);
-    fname += tmp;
-    return fname;
-}
-
-template <typename T, typename S>
-void MergeSorter<T, S>::merge()
-{
-    S sorter;
-    std::vector< SequentialFileArrayRead<T> *> fileParts;
-    size_t count(0);
-    for(size_t i(0); i < _chunkCount; i++) {
-        std::unique_ptr< SequentialFileArrayRead<T> > part(new SequentialFileArrayRead<T>(genName(i)));
-        size_t sz = part->size();
-        if (sz > 0) {
-            fileParts.push_back(part.release());
-        } else {
-            part->erase();
-        }
-        count += sz;
-    }
-
-    std::vector<T> cachedValue;
-    for(size_t i(0), m(fileParts.size()); i < m; i++) {
-        cachedValue.push_back(fileParts[i]->getNext());
-    }
-    SequentialFileArrayWrite<T> merged(_name);
-    for(size_t j(0); j < count; j++) {
-        size_t firstIndex(0);
-        for(size_t i(1), m(cachedValue.size()); i < m; i++) {
-            if (sorter.cmp(cachedValue[i], cachedValue[firstIndex])) {
-                firstIndex = i;
-            }
-        }
-        merged.push_back(cachedValue[firstIndex]);
-        if ( ! fileParts[firstIndex]->hasNext() ) {
-            fileParts[firstIndex]->erase();
-            delete fileParts[firstIndex];
-            fileParts.erase(fileParts.begin()+firstIndex);
-            cachedValue.erase(cachedValue.begin()+firstIndex);
-        } else {
-            cachedValue[firstIndex] = fileParts[firstIndex]->getNext();
-        }
-    }
-}
-
-template <typename T, typename S>
-void MergeSorter<T, S>::sortChunk()
-{
-    S sorter;
-    sorter.sort(&_chunk[0], _chunk.size());
-    FastOS_File chunkFile(genName(_chunkCount).c_str());
-    chunkFile.EnableDirectIO();
-    if (chunkFile.OpenWriteOnlyTruncate()) {
-        chunkFile.CheckedWrite(&_chunk[0], _chunk.size()*sizeof(_chunk[0]));
-    }
-    chunkFile.Close();
-    _chunkCount++;
-    _chunk.clear();
-}
-
-template <typename T>
 SequentialReadModifyWriteVector<T>::SequentialReadModifyWriteVector()
     : Vector(),
       _rp(0),
@@ -137,17 +21,6 @@ SequentialReadModifyWriteVector<T>::SequentialReadModifyWriteVector(size_t sz)
 { }
 
 template <typename T>
-SequentialReadModifyWriteVector<T>::~SequentialReadModifyWriteVector() { }
-
-template <typename T, typename R, typename W>
-SequentialReaderWriter<T, R, W>::SequentialReaderWriter(R & reader, W & writer)
-    : _reader(reader),
-      _writer(writer)
-{
-    next();
-}
-
-template <typename T, typename R, typename W>
-SequentialReaderWriter<T, R, W>::~SequentialReaderWriter() { }
+SequentialReadModifyWriteVector<T>::~SequentialReadModifyWriteVector() = default;
 
 }
diff --git a/searchlib/src/vespa/searchlib/util/stringenum.cpp b/searchlib/src/vespa/searchlib/util/stringenum.cpp
index 01c4d4e785e..9744d39746e 100644
--- a/searchlib/src/vespa/searchlib/util/stringenum.cpp
+++ b/searchlib/src/vespa/searchlib/util/stringenum.cpp
@@ -13,20 +13,19 @@ namespace search::util {
 static inline char *
 StripString(char *str)
 {
-    char *first = NULL; // first non-space char
-    char *last  = NULL; // last non-space char
+    char *last  = nullptr; // last non-space char
 
-    if (str == NULL)
-        return NULL;
+    if (str == nullptr)
+        return nullptr;
 
     for (; *str != '\0' && isspace(*str); str++);
-    first = str;
+    char *first = str;
 
     for (; *str != '\0'; str++)
         if (!isspace(*str))
             last = str;
 
-    if (last != NULL)
+    if (last != nullptr)
         *(last + 1) = '\0';
 
     return first;
@@ -76,8 +75,7 @@ StringEnum::Save(const char *filename)
         file.WriteString("\n");
     }
 
-    file.Close();
-    return true;
+    return file.Sync();
 }
 
 
@@ -100,7 +98,7 @@ StringEnum::Load(const char *filename)
     entryCnt   = 0;
 
     pt = StripString(file.ReadLine(line, sizeof(line)));
-    if (pt == NULL || *pt == '\0')
+    if (pt == nullptr || *pt == '\0')
         return false;
     lineNumber++;
 
@@ -108,7 +106,7 @@ StringEnum::Load(const char *filename)
 
     while (!file.Eof()) {
         pt = StripString(file.ReadLine(line, sizeof(line)));
-        if (pt == NULL)  // end of input ?
+        if (pt == nullptr)  // end of input ?
             break;
         lineNumber++;
         if (*pt == '\0') // empty line ?
@@ -121,7 +119,6 @@ StringEnum::Load(const char *filename)
         entryCnt++;
     }
 
-    file.Close();
     if (entries != _numEntries
         || entries != entryCnt) {
         Clear();
@@ -162,7 +159,7 @@ const char *
 StringEnum::Lookup(uint32_t value) const
 {
     if (value >= _numEntries)
-        return NULL;
+        return nullptr;
 
     if (_numEntries > _reverseMap.size())
         CreateReverseMapping();