Refactor: Modernize clang parser and make it run with multiple threads

17 files changed, 573 insertions, 550 deletions

diff --git a/src/clangparser.cpp b/src/clangparser.cpp
index e0a1640..2ca5998 100644
--- a/src/clangparser.cpp
+++ b/src/clangparser.cpp
@@ -20,17 +20,22 @@
 #include "membername.h"
 #include "filename.h"
 #include "tooltip.h"
+#if MULTITHREADED_INPUT
+#include <mutex>
+#endif
+#endif
 
-static Definition *g_currentDefinition=0;
-static MemberDef  *g_currentMemberDef=0;
-static uint        g_currentLine=0;
-static bool        g_searchForBody=FALSE;
-static bool        g_insideBody=FALSE;
-static uint        g_bracketCount=0;
+//--------------------------------------------------------------------------
+
+#if MULTITHREADED_INPUT
+std::mutex g_clangMutex;
 #endif
 
 ClangParser *ClangParser::instance()
 {
+#if MULTITHREADED_INPUT
+  std::lock_guard<std::mutex> lock(g_clangMutex);
+#endif
   if (!s_instance) s_instance = new ClangParser;
   return s_instance;
 }
@@ -40,29 +45,7 @@ ClangParser *ClangParser::s_instance = 0;
 //--------------------------------------------------------------------------
 #if USE_LIBCLANG
 
-class ClangParser::Private
-{
-  public:
-    enum DetectedLang { Detected_Cpp, Detected_ObjC, Detected_ObjCpp };
-    Private() : tu(0), tokens(0), numTokens(0), cursors(0),
-                ufs(0), sources(0), numFiles(0), fileMapping(257),
-                detectedLang(Detected_Cpp)
-    { fileMapping.setAutoDelete(TRUE); }
-    int getCurrentTokenLine();
-    CXIndex index;
-    CXTranslationUnit tu;
-    QCString fileName;
-    CXToken *tokens;
-    uint numTokens;
-    CXCursor *cursors;
-    uint curLine;
-    uint curToken;
-    CXUnsavedFile *ufs;
-    QCString *sources;
-    uint numFiles;
-    QDict<uint> fileMapping;
-    DetectedLang detectedLang;
-};
+enum class DetectedLang { Cpp, ObjC, ObjCpp };
 
 static QCString detab(const QCString &s)
 {
@@ -118,83 +101,89 @@ static QCString detab(const QCString &s)
   return out.get();
 }
 
-/** Callback function called for each include in a translation unit */
-static void inclusionVisitor(CXFile includedFile,
-                             CXSourceLocation* /*inclusionStack*/,
-                             unsigned /*includeLen*/,
-                             CXClientData clientData)
+static QCString keywordToType(const char *keyword)
 {
-  QDict<void> *fileDict = (QDict<void> *)clientData;
-  CXString incFileName = clang_getFileName(includedFile);
-  //printf("--- file %s includes %s\n",fileName,clang_getCString(incFileName));
-  fileDict->insert(clang_getCString(incFileName),(void*)0x8);
-  clang_disposeString(incFileName);
+  static const StringUnorderedSet flowKeywords({
+    "break", "case", "catch", "continue", "default", "do",
+    "else", "finally", "for", "foreach", "for each", "goto",
+    "if", "return", "switch", "throw", "throws", "try",
+    "while", "@try", "@catch", "@finally" });
+  static const StringUnorderedSet typeKeywords({
+    "bool", "char", "double", "float", "int", "long", "object",
+    "short", "signed", "unsigned", "void", "wchar_t", "size_t",
+    "boolean", "id", "SEL", "string", "nullptr" });
+  if (flowKeywords.find(keyword)!=flowKeywords.end()) return "keywordflow";
+  if (typeKeywords.find(keyword)!=typeKeywords.end()) return "keywordtype";
+  return "keyword";
 }
 
-/** filter the \a files and only keep those that are found as include files
- *  within the current translation unit.
- *  @param[in,out] files The list of files to filter.
- */
-void ClangParser::determineInputFilesInSameTu(QStrList &files)
+
+//--------------------------------------------------------------------------
+
+class ClangTUParser::Private
+{
+  public:
+    Private(const ClangParser &p,const FileDef *fd)
+      : parser(p), fileDef(fd) {}
+    const ClangParser &parser;
+    const FileDef *fileDef;
+    CXIndex index;
+    uint curToken = 0;
+    DetectedLang detectedLang = DetectedLang::Cpp;
+    uint numFiles = 0;
+    std::vector<QCString> sources;
+    std::vector<CXUnsavedFile> ufs;
+    std::vector<CXCursor> cursors;
+    std::unordered_map<std::string,uint> fileMapping;
+    CXTranslationUnit tu;
+    CXToken *tokens = 0;
+    uint numTokens = 0;
+    StringVector filesInSameTU;
+
+    // state while parsing sources
+    MemberDef  *currentMemberDef=0;
+    uint        currentLine=0;
+    bool        searchForBody=FALSE;
+    bool        insideBody=FALSE;
+    uint        bracketCount=0;
+};
+
+ClangTUParser::ClangTUParser(const ClangParser &parser,const FileDef *fd)
+  : p(std::make_unique<Private>(parser,fd))
 {
-  // put the files in this translation unit in a dictionary
-  QDict<void> incFound(257);
-  clang_getInclusions(p->tu,
-      inclusionVisitor,
-      (CXClientData)&incFound
-      );
-  // create a new filtered file list
-  QStrList resultIncludes;
-  QStrListIterator it2(files);
-  for (it2.toFirst();it2.current();++it2)
-  {
-    if (incFound.find(it2.current()))
-    {
-      resultIncludes.append(it2.current());
-    }
-  }
-  // replace the original list
-  files=resultIncludes;
 }
 
-void ClangParser::start(const char *fileName,QStrList &filesInTranslationUnit)
+StringVector ClangTUParser::filesInSameTU() const
 {
+  return p->filesInSameTU;
+}
+
+void ClangTUParser::parse()
+{
+  QCString fileName = p->fileDef->absFilePath();
+  p->fileDef->getAllIncludeFilesRecursively(p->filesInSameTU);
+  //printf("ClangTUParser::ClangTUParser(fileName=%s,#filesInSameTU=%d)\n",
+  //    qPrint(fileName),(int)p->filesInSameTU.size());
   bool clangAssistedParsing = Config_getBool(CLANG_ASSISTED_PARSING);
+  bool filterSourceFiles = Config_getBool(FILTER_SOURCE_FILES);
   const StringVector &includePath = Config_getList(INCLUDE_PATH);
   const StringVector &clangOptions = Config_getList(CLANG_OPTIONS);
-  QCString clangCompileDatabase = Config_getString(CLANG_DATABASE_PATH);
   if (!clangAssistedParsing) return;
   //printf("ClangParser::start(%s)\n",fileName);
-  p->fileName = fileName;
   p->index    = clang_createIndex(0, 0);
-  p->curLine  = 1;
   p->curToken = 0;
   int argc=0;
-  std::string error;
-  // load a clang compilation database (https://clang.llvm.org/docs/JSONCompilationDatabase.html)
-  // this only needs to be loaded once, and could be refactored to a higher level function
-  static std::unique_ptr<clang::tooling::CompilationDatabase> db =
-      clang::tooling::CompilationDatabase::loadFromDirectory(clangCompileDatabase.data(), error);
-  int clang_option_len = 0;
+  size_t clang_option_len = 0;
   std::vector<clang::tooling::CompileCommand> command;
-  if (qstrcmp(clangCompileDatabase, "0") != 0)
+  if (p->parser.database()!=nullptr)
   {
-      if (db == nullptr)
-      {
-          // user specified a path, but DB file was not found
-          err("%s using clang compilation database path of: \"%s\"\n", error.c_str(),
-              clangCompileDatabase.data());
-      }
-      else
-      {
-          // check if the file we are parsing is in the DB
-          command = db->getCompileCommands(fileName);
-          if (!command.empty() )
-          {
-              // it's possible to have multiple entries for the same file, so use the last entry
-              clang_option_len = command[command.size()-1].CommandLine.size();
-          }
-      }
+    // check if the file we are parsing is in the DB
+    command = p->parser.database()->getCompileCommands(fileName.data());
+    if (!command.empty() )
+    {
+      // it's possible to have multiple entries for the same file, so use the last entry
+      clang_option_len = command[command.size()-1].CommandLine.size();
+    }
   }
   char **argv = (char**)malloc(sizeof(char*)*
                                (4+Doxygen::inputPaths.size()+
@@ -203,14 +192,19 @@ void ClangParser::start(const char *fileName,QStrList &filesInTranslationUnit)
                                 clang_option_len));
   if (!command.empty() )
   {
-      std::vector<std::string> options = command[command.size()-1].CommandLine;
-      // copy each compiler option used from the database. Skip the first which is compiler exe.
-      for (auto option = options.begin()+1; option != options.end(); option++)
-      {
-          argv[argc++] = qstrdup(option->c_str());
-      }
-      // this extra addition to argv is accounted for as we are skipping the first entry in
-      argv[argc++]=qstrdup("-w"); // finally, turn off warnings.
+    std::vector<std::string> options = command[command.size()-1].CommandLine;
+    // copy each compiler option used from the database. Skip the first which is compiler exe.
+    for (auto option = options.begin()+1; option != options.end(); option++)
+    {
+      argv[argc++] = qstrdup(option->c_str());
+    }
+    // user specified options
+    for (size_t i=0;i<clangOptions.size();i++)
+    {
+      argv[argc++]=qstrdup(clangOptions[i].c_str());
+    }
+    // this extra addition to argv is accounted for as we are skipping the first entry in
+    argv[argc++]=qstrdup("-w"); // finally, turn off warnings.
   }
   else
   {
@@ -218,7 +212,7 @@ void ClangParser::start(const char *fileName,QStrList &filesInTranslationUnit)
     for (const std::string &path : Doxygen::inputPaths)
     {
       QCString inc = QCString("-I")+path.data();
-      argv[argc]=qstrdup(inc.data());
+      argv[argc++]=qstrdup(inc.data());
       //printf("argv[%d]=%s\n",argc,argv[argc]);
     }
     // add external include paths
@@ -241,67 +235,63 @@ void ClangParser::start(const char *fileName,QStrList &filesInTranslationUnit)
     // we use the source file to detected the language. Detection will fail if you
     // pass a bunch of .h files containing ObjC code, and no sources :-(
     SrcLangExt lang = getLanguageFromFileName(fileName);
-    if (lang==SrcLangExt_ObjC || p->detectedLang!=ClangParser::Private::Detected_Cpp)
+    if (lang==SrcLangExt_ObjC || p->detectedLang!=DetectedLang::Cpp)
     {
       QCString fn = fileName;
-      if (p->detectedLang==ClangParser::Private::Detected_Cpp &&
+      if (p->detectedLang!=DetectedLang::Cpp &&
           (fn.right(4).lower()==".cpp" || fn.right(4).lower()==".cxx" ||
            fn.right(3).lower()==".cc" || fn.right(2).lower()==".c"))
       { // fall back to C/C++ once we see an extension that indicates this
-        p->detectedLang = ClangParser::Private::Detected_Cpp;
+        p->detectedLang = DetectedLang::Cpp;
       }
       else if (fn.right(3).lower()==".mm") // switch to Objective C++
       {
-        p->detectedLang = ClangParser::Private::Detected_ObjCpp;
+        p->detectedLang = DetectedLang::ObjCpp;
       }
       else if (fn.right(2).lower()==".m") // switch to Objective C
       {
-        p->detectedLang = ClangParser::Private::Detected_ObjC;
+        p->detectedLang = DetectedLang::ObjC;
       }
     }
-    switch(p->detectedLang)
+    switch (p->detectedLang)
     {
-      case ClangParser::Private::Detected_Cpp:
-        argv[argc++]=qstrdup("c++");
-        break;
-      case ClangParser::Private::Detected_ObjC:
-        argv[argc++]=qstrdup("objective-c");
-        break;
-      case ClangParser::Private::Detected_ObjCpp:
-        argv[argc++]=qstrdup("objective-c++");
-        break;
+      case DetectedLang::Cpp:    argv[argc++]=qstrdup("c++");           break;
+      case DetectedLang::ObjC:   argv[argc++]=qstrdup("objective-c");   break;
+      case DetectedLang::ObjCpp: argv[argc++]=qstrdup("objective-c++"); break;
     }
 
     // provide the input and and its dependencies as unsaved files so we can
     // pass the filtered versions
     argv[argc++]=qstrdup(fileName);
   }
-  static bool filterSourceFiles = Config_getBool(FILTER_SOURCE_FILES);
   //printf("source %s ----------\n%s\n-------------\n\n",
   //    fileName,p->source.data());
-  int numUnsavedFiles = filesInTranslationUnit.count()+1;
+  int numUnsavedFiles = static_cast<int>(p->filesInSameTU.size()+1);
   p->numFiles = numUnsavedFiles;
-  p->sources = new QCString[numUnsavedFiles];
-  p->ufs     = new CXUnsavedFile[numUnsavedFiles];
+  p->sources.resize(numUnsavedFiles);
+  p->ufs.resize(numUnsavedFiles);
   p->sources[0]      = detab(fileToString(fileName,filterSourceFiles,TRUE));
   p->ufs[0].Filename = qstrdup(fileName);
   p->ufs[0].Contents = p->sources[0].data();
   p->ufs[0].Length   = p->sources[0].length();
-  QStrListIterator it(filesInTranslationUnit);
+  p->fileMapping.insert({fileName.data(),0});
   int i=1;
-  for (it.toFirst();it.current() && i<numUnsavedFiles;++it,i++)
+  for (auto it  = p->filesInSameTU.begin();
+            it != p->filesInSameTU.end() && i<numUnsavedFiles;
+          ++it, i++)
   {
-    p->fileMapping.insert(it.current(),new uint(i));
-    p->sources[i]      = detab(fileToString(it.current(),filterSourceFiles,TRUE));
-    p->ufs[i].Filename = qstrdup(it.current());
+    p->fileMapping.insert({it->c_str(),static_cast<uint>(i)});
+    p->sources[i]      = detab(fileToString(it->c_str(),filterSourceFiles,TRUE));
+    p->ufs[i].Filename = qstrdup(it->c_str());
     p->ufs[i].Contents = p->sources[i].data();
     p->ufs[i].Length   = p->sources[i].length();
   }
 
   // let libclang do the actual parsing
   p->tu = clang_parseTranslationUnit(p->index, 0,
-                                     argv, argc, p->ufs, numUnsavedFiles,
+                                     argv, argc, p->ufs.data(), numUnsavedFiles,
                                      CXTranslationUnit_DetailedPreprocessingRecord);
+  //printf("  tu=%p\n",p->tu);
   // free arguments
   for (i=0;i<argc;++i)
   {
@@ -311,9 +301,6 @@ void ClangParser::start(const char *fileName,QStrList &filesInTranslationUnit)
 
   if (p->tu)
   {
-    // filter out any includes not found by the clang parser
-    determineInputFilesInSameTu(filesInTranslationUnit);
-
     // show any warnings that the compiler produced
     int n=clang_getNumDiagnostics(p->tu);
     for (i=0; i!=n; ++i)
@@ -325,105 +312,74 @@ void ClangParser::start(const char *fileName,QStrList &filesInTranslationUnit)
       clang_disposeString(string);
       clang_disposeDiagnostic(diag);
     }
-
-    // create a source range for the given file
-    QFileInfo fi(fileName);
-    CXFile f = clang_getFile(p->tu, fileName);
-    CXSourceLocation fileBegin = clang_getLocationForOffset(p->tu, f, 0);
-    CXSourceLocation fileEnd   = clang_getLocationForOffset(p->tu, f, p->ufs[0].Length);
-    CXSourceRange    fileRange = clang_getRange(fileBegin, fileEnd);
-
-    // produce a token stream for the file
-    clang_tokenize(p->tu,fileRange,&p->tokens,&p->numTokens);
-
-    // produce cursors for each token in the stream
-    p->cursors=new CXCursor[p->numTokens];
-    clang_annotateTokens(p->tu,p->tokens,p->numTokens,p->cursors);
   }
   else
   {
     p->tokens    = 0;
     p->numTokens = 0;
-    p->cursors   = 0;
-    err("clang: Failed to parse translation unit %s\n",fileName);
-  }
-}
-
-void ClangParser::switchToFile(const char *fileName)
-{
-  if (p->tu)
-  {
-    delete[] p->cursors;
-    clang_disposeTokens(p->tu,p->tokens,p->numTokens);
-    p->tokens    = 0;
-    p->numTokens = 0;
-    p->cursors   = 0;
-
-    QFileInfo fi(fileName);
-    CXFile f = clang_getFile(p->tu, fileName);
-    uint *pIndex=p->fileMapping.find(fileName);
-    if (pIndex && *pIndex<p->numFiles)
-    {
-      uint i=*pIndex;
-      //printf("switchToFile %s: len=%ld\n",fileName,p->ufs[i].Length);
-      CXSourceLocation fileBegin = clang_getLocationForOffset(p->tu, f, 0);
-      CXSourceLocation fileEnd   = clang_getLocationForOffset(p->tu, f, p->ufs[i].Length);
-      CXSourceRange    fileRange = clang_getRange(fileBegin, fileEnd);
-
-      clang_tokenize(p->tu,fileRange,&p->tokens,&p->numTokens);
-      p->cursors=new CXCursor[p->numTokens];
-      clang_annotateTokens(p->tu,p->tokens,p->numTokens,p->cursors);
-
-      p->curLine  = 1;
-      p->curToken = 0;
-    }
-    else
-    {
-      err("clang: Failed to find input file %s in mapping\n",fileName);
-    }
+    p->cursors.clear();
+    err("clang: Failed to parse translation unit %s\n",qPrint(fileName));
   }
 }
 
-void ClangParser::finish()
+ClangTUParser::~ClangTUParser()
 {
+  //printf("ClangTUParser::~ClangTUParser() tu=%p\n",p->tu);
   static bool clangAssistedParsing = Config_getBool(CLANG_ASSISTED_PARSING);
   if (!clangAssistedParsing) return;
   if (p->tu)
   {
-    //printf("ClangParser::finish()\n");
-    delete[] p->cursors;
+    p->cursors.clear();
     clang_disposeTokens(p->tu,p->tokens,p->numTokens);
     clang_disposeTranslationUnit(p->tu);
     clang_disposeIndex(p->index);
     p->fileMapping.clear();
     p->tokens    = 0;
     p->numTokens = 0;
-    p->cursors   = 0;
   }
   for (uint i=0;i<p->numFiles;i++)
   {
     free((void *)p->ufs[i].Filename);
   }
-  delete[] p->ufs;
-  delete[] p->sources;
-  p->ufs       = 0;
-  p->sources   = 0;
+  p->ufs.clear();
+  p->sources.clear();
   p->numFiles  = 0;
   p->tu        = 0;
 }
 
-int ClangParser::Private::getCurrentTokenLine()
+void ClangTUParser::switchToFile(FileDef *fd)
 {
-  uint l, c;
-  if (numTokens==0) return 1;
-  // guard against filters that reduce the number of lines
-  if (curToken>=numTokens) curToken=numTokens-1;
-  CXSourceLocation start = clang_getTokenLocation(tu,tokens[curToken]);
-  clang_getSpellingLocation(start, 0, &l, &c, 0);
-  return l;
+  //printf("ClangTUParser::switchToFile(%s)\n",qPrint(fd->absFilePath()));
+  if (p->tu)
+  {
+    p->cursors.clear();
+    clang_disposeTokens(p->tu,p->tokens,p->numTokens);
+    p->tokens    = 0;
+    p->numTokens = 0;
+
+    CXFile f = clang_getFile(p->tu, fd->absFilePath());
+    auto it = p->fileMapping.find(fd->absFilePath().data());
+    if (it!=p->fileMapping.end() && it->second < p->numFiles)
+    {
+      uint i = it->second;
+      //printf("switchToFile %s: len=%ld\n",fileName,p->ufs[i].Length);
+      CXSourceLocation fileBegin = clang_getLocationForOffset(p->tu, f, 0);
+      CXSourceLocation fileEnd   = clang_getLocationForOffset(p->tu, f, p->ufs[i].Length);
+      CXSourceRange    fileRange = clang_getRange(fileBegin, fileEnd);
+
+      clang_tokenize(p->tu,fileRange,&p->tokens,&p->numTokens);
+      p->cursors.resize(p->numTokens);
+      clang_annotateTokens(p->tu,p->tokens,p->numTokens,p->cursors.data());
+      p->curToken = 0;
+    }
+    else
+    {
+      err("clang: Failed to find input file %s in mapping\n",qPrint(fd->absFilePath()));
+    }
+  }
 }
 
-QCString ClangParser::lookup(uint line,const char *symbol)
+QCString ClangTUParser::lookup(uint line,const char *symbol)
 {
   //printf("ClangParser::lookup(%d,%s)\n",line,symbol);
   QCString result;
@@ -431,19 +387,30 @@ QCString ClangParser::lookup(uint line,const char *symbol)
   static bool clangAssistedParsing = Config_getBool(CLANG_ASSISTED_PARSING);
   if (!clangAssistedParsing) return result;
 
+  auto getCurrentTokenLine = [=]() -> uint
+  {
+    uint l, c;
+    if (p->numTokens==0) return 1;
+    // guard against filters that reduce the number of lines
+    if (p->curToken>=p->numTokens) p->curToken=p->numTokens-1;
+    CXSourceLocation start = clang_getTokenLocation(p->tu,p->tokens[p->curToken]);
+    clang_getSpellingLocation(start, 0, &l, &c, 0);
+    return l;
+  };
+
   int sl = strlen(symbol);
-  uint l = p->getCurrentTokenLine();
+  uint l = getCurrentTokenLine();
   while (l>=line && p->curToken>0)
   {
     if (l==line) // already at the right line
     {
       p->curToken--; // linear search to start of the line
-      l = p->getCurrentTokenLine();
+      l = getCurrentTokenLine();
     }
     else
     {
       p->curToken/=2; // binary search backward
-      l = p->getCurrentTokenLine();
+      l = getCurrentTokenLine();
     }
   }
   bool found=FALSE;
@@ -468,7 +435,7 @@ QCString ClangParser::lookup(uint line,const char *symbol)
         {
           break; // end of token stream
         }
-        l = p->getCurrentTokenLine();
+        l = getCurrentTokenLine();
         clang_disposeString(tokenString);
         tokenString = clang_getTokenSpelling(p->tu, p->tokens[p->curToken]);
         ts = clang_getCString(tokenString);
@@ -505,7 +472,7 @@ QCString ClangParser::lookup(uint line,const char *symbol)
     p->curToken++;
     if (p->curToken<p->numTokens)
     {
-      l = p->getCurrentTokenLine();
+      l = getCurrentTokenLine();
     }
   }
   //if (!found)
@@ -519,78 +486,23 @@ QCString ClangParser::lookup(uint line,const char *symbol)
   return result;
 }
 
-static QCString keywordToType(const char *keyword)
-{
-  static bool init=TRUE;
-  static QDict<void> flowKeywords(47);
-  static QDict<void> typeKeywords(47);
-  if (init)
-  {
-    flowKeywords.insert("break",(void*)0x8);
-    flowKeywords.insert("case",(void*)0x8);
-    flowKeywords.insert("catch",(void*)0x8);
-    flowKeywords.insert("continue",(void*)0x8);
-    flowKeywords.insert("default",(void*)0x8);
-    flowKeywords.insert("do",(void*)0x8);
-    flowKeywords.insert("else",(void*)0x8);
-    flowKeywords.insert("finally",(void*)0x8);
-    flowKeywords.insert("for",(void*)0x8);
-    flowKeywords.insert("foreach",(void*)0x8);
-    flowKeywords.insert("for each",(void*)0x8);
-    flowKeywords.insert("goto",(void*)0x8);
-    flowKeywords.insert("if",(void*)0x8);
-    flowKeywords.insert("return",(void*)0x8);
-    flowKeywords.insert("switch",(void*)0x8);
-    flowKeywords.insert("throw",(void*)0x8);
-    flowKeywords.insert("throws",(void*)0x8);
-    flowKeywords.insert("try",(void*)0x8);
-    flowKeywords.insert("while",(void*)0x8);
-    flowKeywords.insert("@try",(void*)0x8);
-    flowKeywords.insert("@catch",(void*)0x8);
-    flowKeywords.insert("@finally",(void*)0x8);
-
-    typeKeywords.insert("bool",(void*)0x8);
-    typeKeywords.insert("char",(void*)0x8);
-    typeKeywords.insert("double",(void*)0x8);
-    typeKeywords.insert("float",(void*)0x8);
-    typeKeywords.insert("int",(void*)0x8);
-    typeKeywords.insert("long",(void*)0x8);
-    typeKeywords.insert("object",(void*)0x8);
-    typeKeywords.insert("short",(void*)0x8);
-    typeKeywords.insert("signed",(void*)0x8);
-    typeKeywords.insert("unsigned",(void*)0x8);
-    typeKeywords.insert("void",(void*)0x8);
-    typeKeywords.insert("wchar_t",(void*)0x8);
-    typeKeywords.insert("size_t",(void*)0x8);
-    typeKeywords.insert("boolean",(void*)0x8);
-    typeKeywords.insert("id",(void*)0x8);
-    typeKeywords.insert("SEL",(void*)0x8);
-    typeKeywords.insert("string",(void*)0x8);
-    typeKeywords.insert("nullptr",(void*)0x8);
-    init=FALSE;
-  }
-  if (flowKeywords[keyword]) return "keywordflow";
-  if (typeKeywords[keyword]) return "keywordtype";
-  return "keyword";
-}
 
-static void writeLineNumber(CodeOutputInterface &ol,FileDef *fd,uint line)
+void ClangTUParser::writeLineNumber(CodeOutputInterface &ol,FileDef *fd,uint line)
 {
   Definition *d = fd ? fd->getSourceDefinition(line) : 0;
   if (d && d->isLinkable())
   {
-    g_currentDefinition=d;
-    g_currentLine=line;
+    p->currentLine=line;
     MemberDef *md = fd->getSourceMember(line);
     if (md && md->isLinkable())  // link to member
     {
-      if (g_currentMemberDef!=md) // new member, start search for body
+      if (p->currentMemberDef!=md) // new member, start search for body
       {
-        g_searchForBody=TRUE;
-        g_insideBody=FALSE;
-        g_bracketCount=0;
+        p->searchForBody=TRUE;
+        p->insideBody=FALSE;
+        p->bracketCount=0;
       }
-      g_currentMemberDef=md;
+      p->currentMemberDef=md;
       ol.writeLineNumber(md->getReference(),
                          md->getOutputFileBase(),
                          md->anchor(),
@@ -598,7 +510,7 @@ static void writeLineNumber(CodeOutputInterface &ol,FileDef *fd,uint line)
     }
     else // link to compound
     {
-      g_currentMemberDef=0;
+      p->currentMemberDef=0;
       ol.writeLineNumber(d->getReference(),
                          d->getOutputFileBase(),
                          d->anchor(),
@@ -621,8 +533,8 @@ static void writeLineNumber(CodeOutputInterface &ol,FileDef *fd,uint line)
   //printf("writeLineNumber(%d) g_searchForBody=%d\n",line,g_searchForBody);
 }
 
-static void codifyLines(CodeOutputInterface &ol,FileDef *fd,const char *text,
-                        uint &line,uint &column,const char *fontClass=0)
+void ClangTUParser::codifyLines(CodeOutputInterface &ol,FileDef *fd,const char *text,
+                        uint &line,uint &column,const char *fontClass)
 {
   if (fontClass) ol.startFontClass(fontClass);
   const char *p=text,*sp=p;
@@ -657,7 +569,7 @@ static void codifyLines(CodeOutputInterface &ol,FileDef *fd,const char *text,
   if (fontClass) ol.endFontClass();
 }
 
-static void writeMultiLineCodeLink(CodeOutputInterface &ol,
+void ClangTUParser::writeMultiLineCodeLink(CodeOutputInterface &ol,
                   FileDef *fd,uint &line,uint &column,
                   Definition *d,
                   const char *text)
@@ -698,7 +610,7 @@ static void writeMultiLineCodeLink(CodeOutputInterface &ol,
   }
 }
 
-void ClangParser::linkInclude(CodeOutputInterface &ol,FileDef *fd,
+void ClangTUParser::linkInclude(CodeOutputInterface &ol,FileDef *fd,
     uint &line,uint &column,const char *text)
 {
   QCString incName = text;
@@ -732,7 +644,7 @@ void ClangParser::linkInclude(CodeOutputInterface &ol,FileDef *fd,
   }
 }
 
-void ClangParser::linkMacro(CodeOutputInterface &ol,FileDef *fd,
+void ClangTUParser::linkMacro(CodeOutputInterface &ol,FileDef *fd,
     uint &line,uint &column,const char *text)
 {
   MemberName *mn=Doxygen::functionNameLinkedMap->find(text);
@@ -751,7 +663,7 @@ void ClangParser::linkMacro(CodeOutputInterface &ol,FileDef *fd,
 }
 
 
-void ClangParser::linkIdentifier(CodeOutputInterface &ol,FileDef *fd,
+void ClangTUParser::linkIdentifier(CodeOutputInterface &ol,FileDef *fd,
     uint &line,uint &column,const char *text,int tokenIndex)
 {
   CXCursor c = p->cursors[tokenIndex];
@@ -782,11 +694,11 @@ void ClangParser::linkIdentifier(CodeOutputInterface &ol,FileDef *fd,
   //}
   if (d && d->isLinkable())
   {
-    if (g_insideBody &&
-        g_currentMemberDef && d->definitionType()==Definition::TypeMember &&
-        (g_currentMemberDef!=d || g_currentLine<line)) // avoid self-reference
+    if (p->insideBody &&
+        p->currentMemberDef && d->definitionType()==Definition::TypeMember &&
+        (p->currentMemberDef!=d || p->currentLine<line)) // avoid self-reference
     {
-      addDocCrossReference(g_currentMemberDef,dynamic_cast<MemberDef *>(d));
+      addDocCrossReference(p->currentMemberDef,dynamic_cast<MemberDef *>(d));
     }
     writeMultiLineCodeLink(ol,fd,line,column,d,text);
   }
@@ -797,45 +709,44 @@ void ClangParser::linkIdentifier(CodeOutputInterface &ol,FileDef *fd,
   clang_disposeString(usr);
 }
 
-static void detectFunctionBody(const char *s)
+void ClangTUParser::detectFunctionBody(const char *s)
 {
   //printf("punct=%s g_searchForBody=%d g_insideBody=%d g_bracketCount=%d\n",
   //  s,g_searchForBody,g_insideBody,g_bracketCount);
 
-  if (g_searchForBody && (qstrcmp(s,":")==0 || qstrcmp(s,"{")==0)) // start of 'body' (: is for constructor)
+  if (p->searchForBody && (qstrcmp(s,":")==0 || qstrcmp(s,"{")==0)) // start of 'body' (: is for constructor)
   {
-    g_searchForBody=FALSE;
-    g_insideBody=TRUE;
+    p->searchForBody=FALSE;
+    p->insideBody=TRUE;
   }
-  else if (g_searchForBody && qstrcmp(s,";")==0) // declaration only
+  else if (p->searchForBody && qstrcmp(s,";")==0) // declaration only
   {
-    g_searchForBody=FALSE;
-    g_insideBody=FALSE;
+    p->searchForBody=FALSE;
+    p->insideBody=FALSE;
   }
-  if (g_insideBody && qstrcmp(s,"{")==0) // increase scoping level
+  if (p->insideBody && qstrcmp(s,"{")==0) // increase scoping level
   {
-    g_bracketCount++;
+    p->bracketCount++;
   }
-  if (g_insideBody && qstrcmp(s,"}")==0) // decrease scoping level
+  if (p->insideBody && qstrcmp(s,"}")==0) // decrease scoping level
   {
-    g_bracketCount--;
-    if (g_bracketCount<=0) // got outside of function body
+    p->bracketCount--;
+    if (p->bracketCount<=0) // got outside of function body
     {
-      g_insideBody=FALSE;
-      g_bracketCount=0;
+      p->insideBody=FALSE;
+      p->bracketCount=0;
     }
   }
 }
 
-void ClangParser::writeSources(CodeOutputInterface &ol,FileDef *fd)
+void ClangTUParser::writeSources(CodeOutputInterface &ol,FileDef *fd)
 {
   // (re)set global parser state
-  g_currentDefinition=0;
-  g_currentMemberDef=0;
-  g_currentLine=0;
-  g_searchForBody=FALSE;
-  g_insideBody=FALSE;
-  g_bracketCount=0;
+  p->currentMemberDef=0;
+  p->currentLine=0;
+  p->searchForBody=FALSE;
+  p->insideBody=FALSE;
+  p->bracketCount=0;
 
   unsigned int line=1,column=1;
   QCString lineNumber,lineAnchor;
@@ -939,16 +850,47 @@ void ClangParser::writeSources(CodeOutputInterface &ol,FileDef *fd)
   ol.endCodeLine();
 }
 
-ClangParser::ClangParser()
+//--------------------------------------------------------------------------
+
+class ClangParser::Private
+{
+  public:
+    Private()
+    {
+      std::string error;
+      QCString clangCompileDatabase = Config_getString(CLANG_DATABASE_PATH);
+      // load a clang compilation database (https://clang.llvm.org/docs/JSONCompilationDatabase.html)
+      db = clang::tooling::CompilationDatabase::loadFromDirectory(clangCompileDatabase.data(), error);
+      if (clangCompileDatabase!="0" && db==nullptr)
+      {
+          // user specified a path, but DB file was not found
+          err("%s using clang compilation database path of: \"%s\"\n", error.c_str(),
+              clangCompileDatabase.data());
+      }
+    }
+
+    std::unique_ptr<clang::tooling::CompilationDatabase> db;
+};
+
+const clang::tooling::CompilationDatabase *ClangParser::database() const
+{
+  return p->db.get();
+}
+
+ClangParser::ClangParser() : p(std::make_unique<Private>())
 {
-  p = new Private;
 }
 
 ClangParser::~ClangParser()
 {
-  delete p;
 }
 
+std::unique_ptr<ClangTUParser> ClangParser::createTUParser(const FileDef *fd) const
+{
+  return std::make_unique<ClangTUParser>(*this,fd);
+}
+
+
 //--------------------------------------------------------------------------
 #else // use stubbed functionality in case libclang support is disabled.
 
@@ -982,7 +924,6 @@ ClangParser::~ClangParser()
 {
 }
 
-
 #endif
 //--------------------------------------------------------------------------
 
diff --git a/src/clangparser.h b/src/clangparser.h
index 8bb9aba..07907a6 100644
--- a/src/clangparser.h
+++ b/src/clangparser.h
@@ -3,9 +3,73 @@
 
 #include <qcstring.h>
 #include <qstrlist.h>
+#include "containers.h"
+#include <memory>
 
 class CodeOutputInterface;
 class FileDef;
+class ClangParser;
+class Definition;
+
+namespace clang { namespace tooling {
+  class CompilationDatabase;
+} }
+
+/** @brief Clang parser object for a single translation unit, which consists of a source file
+ *  and the directly or indirectly included headers
+ */
+class ClangTUParser
+{
+  public:
+    ClangTUParser(const ClangParser &parser,const FileDef *fd);
+    virtual ~ClangTUParser();
+
+    /** Parse the file given at construction time as a translation unit
+     *  This file should already be preprocessed by doxygen preprocessor at the time of calling.
+     */
+    void parse();
+
+    /** Switches to another file within the translation unit started with start().
+     *  @param[in] fileName The name of the file to switch to.
+     */
+    void switchToFile(FileDef *fd);
+
+    /** Returns the list of files for this translation unit */
+    StringVector filesInSameTU() const;
+
+    /** Looks for \a symbol which should be found at \a line.
+     *  returns a clang unique reference to the symbol.
+     */
+    QCString lookup(uint line,const char *symbol);
+
+    /** writes the syntax highlighted source code for a file
+     *  @param[out] ol The output generator list to write to.
+     *  @param[in]  fd The file to write sources for.
+     */
+    void writeSources(CodeOutputInterface &ol,FileDef *fd);
+
+  private:
+    void detectFunctionBody(const char *s);
+    void writeLineNumber(CodeOutputInterface &ol,FileDef *fd,uint line);
+    void codifyLines(CodeOutputInterface &ol,FileDef *fd,const char *text,
+                     uint &line,uint &column,const char *fontClass=0);
+    void writeMultiLineCodeLink(CodeOutputInterface &ol,
+                                FileDef *fd,uint &line,uint &column,
+                                Definition *d, const char *text);
+    void linkIdentifier(CodeOutputInterface &ol,FileDef *fd,
+                        uint &line,uint &column,
+                        const char *text,int tokenIndex);
+    void linkMacro(CodeOutputInterface &ol,FileDef *fd,
+                   uint &line,uint &column,
+                   const char *text);
+    void linkInclude(CodeOutputInterface &ol,FileDef *fd,
+                   uint &line,uint &column,
+                   const char *text);
+    ClangTUParser(const ClangTUParser &) = delete;
+    ClangTUParser &operator=(const ClangTUParser &) = delete;
+    class Private;
+    std::unique_ptr<Private> p;
+};
 
 /** @brief Wrapper for to let libclang assisted parsing. */
 class ClangParser
@@ -13,16 +77,20 @@ class ClangParser
   public:
     /** Returns the one and only instance of the class */
     static ClangParser *instance();
-    
+
+    std::unique_ptr<ClangTUParser> createTUParser(const FileDef *fd) const;
+    const clang::tooling::CompilationDatabase *database() const;
+
+#if 0
     /** Start parsing a file.
      *  @param[in] fileName The name of the file to parse.
      *  @param[in,out] filesInTranslationUnit Other files that are
      *                 part of the input and included by the file.
      *                 The function will return a subset of the files,
-     *                 only including the ones that were actually found 
+     *                 only including the ones that were actually found
      *                 during parsing.
      */
-    void start(const char *fileName,QStrList &filesInTranslationUnit);
+    void start(const char *fileName,StringVector &filesInTranslationUnit);
 
     /** Switches to another file within the translation unit started
      *  with start().
@@ -45,8 +113,10 @@ class ClangParser
      *  @param[in]  fd The file to write sources for.
      */
     void writeSources(CodeOutputInterface &ol,FileDef *fd);
+#endif
 
   private:
+#if 0
     void linkIdentifier(CodeOutputInterface &ol,FileDef *fd,
                         uint &line,uint &column,
                         const char *text,int tokenIndex);
@@ -56,9 +126,9 @@ class ClangParser
     void linkInclude(CodeOutputInterface &ol,FileDef *fd,
                    uint &line,uint &column,
                    const char *text);
-    void determineInputFilesInSameTu(QStrList &filesInTranslationUnit);
+#endif
     class Private;
-    Private *p;
+    std::unique_ptr<Private> p;
     ClangParser();
     virtual ~ClangParser();
     static ClangParser *s_instance;
diff --git a/src/doxygen.cpp b/src/doxygen.cpp
index 5ac1980..8c739ad 100644
--- a/src/doxygen.cpp
+++ b/src/doxygen.cpp
@@ -104,6 +104,7 @@
 #include "plantuml.h"
 #include "stlsupport.h"
 #include "threadpool.h"
+#include "clangparser.h"
 
 // provided by the generated file resources.cpp
 extern void initResources();
@@ -7499,50 +7500,48 @@ static void generateFileSources()
         {
           if (fd->isSource() && !fd->isReference())
           {
-            QStrList filesInSameTu;
-            fd->getAllIncludeFilesRecursively(filesInSameTu);
-            fd->startParsing();
+            auto clangParser = ClangParser::instance()->createTUParser(fd.get());
             if (fd->generateSourceFile() && !g_useOutputTemplate) // sources need to be shown in the output
             {
               msg("Generating code for file %s...\n",fd->docName().data());
-              fd->writeSource(*g_outputList,FALSE,filesInSameTu);
+              clangParser->parse();
+              fd->writeSource(*g_outputList,clangParser.get());
 
             }
             else if (!fd->isReference() && Doxygen::parseSourcesNeeded)
               // we needed to parse the sources even if we do not show them
             {
               msg("Parsing code for file %s...\n",fd->docName().data());
-              fd->parseSource(FALSE,filesInSameTu);
+              clangParser->parse();
+              fd->parseSource(clangParser.get());
             }
 
-            char *incFile = filesInSameTu.first();
-            while (incFile && filesToProcess.find(incFile)!=filesToProcess.end())
+            for (auto incFile : clangParser->filesInSameTU())
             {
-              if (fd->absFilePath()!=incFile && processedFiles.find(incFile)==processedFiles.end())
+              if (filesToProcess.find(incFile)!=filesToProcess.end() &&  // part of input
+                  fd->absFilePath()!=incFile &&                          // not same file
+                  processedFiles.find(incFile)==processedFiles.end())    // not yet marked as processed
               {
-                QStrList moreFiles;
+                StringVector moreFiles;
                 bool ambig;
-                FileDef *ifd=findFileDef(Doxygen::inputNameLinkedMap,incFile,ambig);
+                FileDef *ifd=findFileDef(Doxygen::inputNameLinkedMap,incFile.c_str(),ambig);
                 if (ifd && !ifd->isReference())
                 {
                   if (ifd->generateSourceFile() && !g_useOutputTemplate) // sources need to be shown in the output
                   {
                     msg(" Generating code for file %s...\n",ifd->docName().data());
-                    ifd->writeSource(*g_outputList,TRUE,moreFiles);
-
+                    ifd->writeSource(*g_outputList,clangParser.get());
                   }
                   else if (!ifd->isReference() && Doxygen::parseSourcesNeeded)
                     // we needed to parse the sources even if we do not show them
                   {
                     msg(" Parsing code for file %s...\n",ifd->docName().data());
-                    ifd->parseSource(TRUE,moreFiles);
+                    ifd->parseSource(clangParser.get());
                   }
                   processedFiles.insert(incFile);
                 }
               }
-              incFile = filesInSameTu.next();
             }
-            fd->finishParsing();
             processedFiles.insert(fd->absFilePath().str());
           }
         }
@@ -7554,21 +7553,21 @@ static void generateFileSources()
         {
           if (processedFiles.find(fd->absFilePath().str())==processedFiles.end()) // not yet processed
           {
-            QStrList filesInSameTu;
-            fd->startParsing();
+            auto clangParser = ClangParser::instance()->createTUParser(fd.get());
             if (fd->generateSourceFile() && !Htags::useHtags && !g_useOutputTemplate) // sources need to be shown in the output
             {
               msg("Generating code for file %s...\n",fd->docName().data());
-              fd->writeSource(*g_outputList,FALSE,filesInSameTu);
+              clangParser->parse();
+              fd->writeSource(*g_outputList,clangParser.get());
 
             }
             else if (!fd->isReference() && Doxygen::parseSourcesNeeded)
               // we needed to parse the sources even if we do not show them
             {
               msg("Parsing code for file %s...\n",fd->docName().data());
-              fd->parseSource(FALSE,filesInSameTu);
+              clangParser->parse();
+              fd->parseSource(clangParser.get());
             }
-            fd->finishParsing();
           }
         }
       }
@@ -7580,21 +7579,20 @@ static void generateFileSources()
       {
         for (const auto &fd : *fn)
         {
-          QStrList filesInSameTu;
-          fd->startParsing();
+          StringVector filesInSameTu;
+          fd->getAllIncludeFilesRecursively(filesInSameTu);
           if (fd->generateSourceFile() && !Htags::useHtags && !g_useOutputTemplate) // sources need to be shown in the output
           {
             msg("Generating code for file %s...\n",fd->docName().data());
-            fd->writeSource(*g_outputList,FALSE,filesInSameTu);
+            fd->writeSource(*g_outputList,nullptr);
 
           }
           else if (!fd->isReference() && Doxygen::parseSourcesNeeded)
             // we needed to parse the sources even if we do not show them
           {
             msg("Parsing code for file %s...\n",fd->docName().data());
-            fd->parseSource(FALSE,filesInSameTu);
+            fd->parseSource(nullptr);
           }
-          fd->finishParsing();
         }
       }
     }
@@ -9062,7 +9060,7 @@ static std::unique_ptr<OutlineParserInterface> getParserForFile(const char *fn)
 
 static std::shared_ptr<Entry> parseFile(OutlineParserInterface &parser,
                       FileDef *fd,const char *fn,
-                      bool sameTu,QStrList &filesInSameTu)
+                      ClangTUParser *clangParser,bool newTU)
 {
   QCString fileName=fn;
   QCString extension;
@@ -9110,18 +9108,20 @@ static std::shared_ptr<Entry> parseFile(OutlineParserInterface &parser,
 
   convBuf.addChar('\0');
 
-  if (Doxygen::clangAssistedParsing && !sameTu)
-  {
-    fd->getAllIncludeFilesRecursively(filesInSameTu);
-  }
-
   std::shared_ptr<Entry> fileRoot = std::make_shared<Entry>();
   // use language parse to parse the file
-  parser.parseInput(fileName,convBuf.data(),fileRoot,sameTu,filesInSameTu);
+  if (clangParser)
+  {
+    if (newTU) clangParser->parse();
+    clangParser->switchToFile(fd);
+  }
+  parser.parseInput(fileName,convBuf.data(),fileRoot,clangParser);
   fileRoot->setFileDef(fd);
   return fileRoot;
 }
 
+#if MULTITHREADED_INPUT
+
 //! parse the list of input files
 static void parseFiles(const std::shared_ptr<Entry> &root)
 {
@@ -9137,7 +9137,12 @@ static void parseFiles(const std::shared_ptr<Entry> &root)
       filesToProcess.insert(s);
     }
 
+    std::mutex processedFilesLock;
     // process source files (and their include dependencies)
+    std::size_t numThreads = std::thread::hardware_concurrency();
+    msg("Processing input using %lu threads.\n",numThreads);
+    ThreadPool threadPool(numThreads);
+    std::vector< std::future< std::vector< std::shared_ptr<Entry> > > > results;
     for (const auto &s : g_inputFiles)
     {
       bool ambig;
@@ -9145,70 +9150,89 @@ static void parseFiles(const std::shared_ptr<Entry> &root)
       ASSERT(fd!=0);
       if (fd->isSource() && !fd->isReference()) // this is a source file
       {
-        QStrList filesInSameTu;
-        std::unique_ptr<OutlineParserInterface> parser { getParserForFile(s.c_str()) };
-        parser->startTranslationUnit(s.c_str());
-        std::shared_ptr<Entry> fileRoot = parseFile(*parser.get(),fd,s.c_str(),FALSE,filesInSameTu);
-        root->moveToSubEntryAndKeep(fileRoot);
-        //printf("  got %d extra files in tu\n",filesInSameTu.count());
-
-        // Now process any include files in the same translation unit
-        // first. When libclang is used this is much more efficient.
-        char *incFile = filesInSameTu.first();
-        while (incFile && filesToProcess.find(incFile)!=filesToProcess.end())
-        {
-          if (qstrcmp(incFile,s.c_str()) && processedFiles.find(incFile)==processedFiles.end())
+        // lambda representing the work to executed by a thread
+        auto processFile = [s,&filesToProcess,&processedFilesLock,&processedFiles]() {
+          bool ambig;
+          std::vector< std::shared_ptr<Entry> > roots;
+          FileDef *fd = findFileDef(Doxygen::inputNameLinkedMap,s.c_str(),ambig);
+          auto clangParser = ClangParser::instance()->createTUParser(fd);
+          auto parser = getParserForFile(s.c_str());
+          auto fileRoot { parseFile(*parser.get(),fd,s.c_str(),clangParser.get(),true) };
+          roots.push_back(fileRoot);
+
+          // Now process any include files in the same translation unit
+          // first. When libclang is used this is much more efficient.
+          for (auto incFile : clangParser->filesInSameTU())
           {
-            FileDef *ifd=findFileDef(Doxygen::inputNameLinkedMap,incFile,ambig);
-            if (ifd && !ifd->isReference())
+            if (filesToProcess.find(incFile)!=filesToProcess.end())
             {
-              QStrList moreFiles;
-              //printf("  Processing %s in same translation unit as %s\n",incFile,s->c_str());
-              fileRoot = parseFile(*parser.get(),ifd,incFile,TRUE,moreFiles);
-              root->moveToSubEntryAndKeep(fileRoot);
-              processedFiles.insert(incFile);
+              bool needsToBeProcessed;
+              {
+                std::lock_guard<std::mutex> lock(processedFilesLock);
+                needsToBeProcessed = processedFiles.find(incFile)==processedFiles.end();
+                if (needsToBeProcessed) processedFiles.insert(incFile);
+              }
+              if (incFile!=s && needsToBeProcessed)
+              {
+                FileDef *ifd=findFileDef(Doxygen::inputNameLinkedMap,incFile.c_str(),ambig);
+                if (ifd && !ifd->isReference())
+                {
+                  //printf("  Processing %s in same translation unit as %s\n",incFile,s->c_str());
+                  fileRoot = parseFile(*parser.get(),ifd,incFile.c_str(),clangParser.get(),false);
+                  roots.push_back(fileRoot);
+                }
+              }
             }
           }
-          incFile = filesInSameTu.next();
-        }
-        parser->finishTranslationUnit();
-        processedFiles.insert(s);
+          return roots;
+        };
+        // dispatch the work and collect the future results
+        results.emplace_back(threadPool.queue(processFile));
+      }
+    }
+    // synchronise with the Entry result lists produced and add them to the root
+    for (auto &f : results)
+    {
+      auto l = f.get();
+      for (auto &e : l)
+      {
+        root->moveToSubEntryAndKeep(e);
       }
     }
     // process remaining files
+    results.clear();
     for (const auto &s : g_inputFiles)
     {
       if (processedFiles.find(s)==processedFiles.end()) // not yet processed
       {
-        bool ambig;
-        QStrList filesInSameTu;
-        FileDef *fd=findFileDef(Doxygen::inputNameLinkedMap,s.c_str(),ambig);
-        ASSERT(fd!=0);
-        std::unique_ptr<OutlineParserInterface> parser { getParserForFile(s.c_str()) };
-        parser->startTranslationUnit(s.c_str());
-        std::shared_ptr<Entry> fileRoot = parseFile(*parser.get(),fd,s.c_str(),FALSE,filesInSameTu);
-        root->moveToSubEntryAndKeep(fileRoot);
-        parser->finishTranslationUnit();
-        processedFiles.insert(s);
+        // lambda representing the work to executed by a thread
+        auto processFile = [s]() {
+          bool ambig;
+          std::vector< std::shared_ptr<Entry> > roots;
+          FileDef *fd=findFileDef(Doxygen::inputNameLinkedMap,s.c_str(),ambig);
+          auto clangParser = ClangParser::instance()->createTUParser(fd);
+          auto parser { getParserForFile(s.c_str()) };
+          auto fileRoot = parseFile(*parser.get(),fd,s.c_str(),clangParser.get(),true);
+          roots.push_back(fileRoot);
+          return roots;
+        };
+        // dispatch the work and collect the future results
+        results.emplace_back(threadPool.queue(processFile));
+      }
+    }
+    // synchronise with the Entry result lists produced and add them to the root
+    for (auto &f : results)
+    {
+      auto l = f.get();
+      for (auto &e : l)
+      {
+        root->moveToSubEntryAndKeep(e);
       }
     }
   }
   else // normal processing
 #endif
   {
-#if !MULTITHREADED_INPUT
-    for (const auto &s : g_inputFiles)
-    {
-      bool ambig;
-      QStrList filesInSameTu;
-      FileDef *fd=findFileDef(Doxygen::inputNameLinkedMap,s.c_str(),ambig);
-      ASSERT(fd!=0);
-      std::unique_ptr<OutlineParserInterface> parser { getParserForFile(s.c_str()) };
-      parser->startTranslationUnit(s.c_str());
-      std::shared_ptr<Entry> fileRoot = parseFile(*parser.get(),fd,s.c_str(),FALSE,filesInSameTu);
-      root->moveToSubEntryAndKeep(fileRoot);
-    }
-#else
     std::size_t numThreads = std::thread::hardware_concurrency();
     msg("Processing input using %lu threads.\n",numThreads);
     ThreadPool threadPool(numThreads);
@@ -9218,12 +9242,10 @@ static void parseFiles(const std::shared_ptr<Entry> &root)
       // lambda representing the work to executed by a thread
       auto processFile = [s]() {
         bool ambig;
-        QStrList filesInSameTu;
         FileDef *fd=findFileDef(Doxygen::inputNameLinkedMap,s.c_str(),ambig);
-        ASSERT(fd!=0);
-        std::unique_ptr<OutlineParserInterface> parser { getParserForFile(s.c_str()) };
-        parser->startTranslationUnit(s.c_str());
-        std::shared_ptr<Entry> fileRoot = parseFile(*parser.get(),fd,s.c_str(),FALSE,filesInSameTu);
+        auto clangParser = ClangParser::instance()->createTUParser(fd);
+        auto parser = getParserForFile(s.c_str());
+        auto fileRoot = parseFile(*parser.get(),fd,s.c_str(),clangParser.get(),true);
         return fileRoot;
       };
       // dispatch the work and collect the future results
@@ -9235,10 +9257,92 @@ static void parseFiles(const std::shared_ptr<Entry> &root)
       root->moveToSubEntryAndKeep(f.get());
     }
 #warning "Multi-threaded input enabled. This is a highly experimental feature. Only use for doxygen development."
+  }
+}
+
+#else // !MULTITHREADED_INPUT
+
+//! parse the list of input files
+static void parseFiles(const std::shared_ptr<Entry> &root)
+{
+#if USE_LIBCLANG
+  if (Doxygen::clangAssistedParsing)
+  {
+    StringUnorderedSet processedFiles;
+
+    // create a dictionary with files to process
+    StringUnorderedSet filesToProcess;
+    for (const auto &s : g_inputFiles)
+    {
+      filesToProcess.insert(s);
+    }
+
+    // process source files (and their include dependencies)
+    for (const auto &s : g_inputFiles)
+    {
+      bool ambig;
+      FileDef *fd=findFileDef(Doxygen::inputNameLinkedMap,s.c_str(),ambig);
+      ASSERT(fd!=0);
+      if (fd->isSource() && !fd->isReference()) // this is a source file
+      {
+        auto clangParser = ClangParser::instance()->createTUParser(fd);
+        auto parser { getParserForFile(s.c_str()) };
+        auto fileRoot = parseFile(*parser.get(),fd,s.c_str(),clangParser.get(),true);
+        root->moveToSubEntryAndKeep(fileRoot);
+        processedFiles.insert(s);
+
+        // Now process any include files in the same translation unit
+        // first. When libclang is used this is much more efficient.
+        for (auto incFile : clangParser->filesInSameTU())
+        {
+          //printf("    file %s\n",incFile.c_str());
+          if (filesToProcess.find(incFile)!=filesToProcess.end() && // file need to be processed
+              processedFiles.find(incFile)==processedFiles.end())   // and is not processed already
+          {
+            FileDef *ifd=findFileDef(Doxygen::inputNameLinkedMap,incFile.c_str(),ambig);
+            if (ifd && !ifd->isReference())
+            {
+              //printf("  Processing %s in same translation unit as %s\n",incFile.c_str(),s.c_str());
+              fileRoot = parseFile(*parser.get(),ifd,incFile.c_str(),clangParser.get(),false);
+              root->moveToSubEntryAndKeep(fileRoot);
+              processedFiles.insert(incFile);
+            }
+          }
+        }
+      }
+    }
+    // process remaining files
+    for (const auto &s : g_inputFiles)
+    {
+      if (processedFiles.find(s)==processedFiles.end()) // not yet processed
+      {
+        bool ambig;
+        FileDef *fd=findFileDef(Doxygen::inputNameLinkedMap,s.c_str(),ambig);
+        auto clangParser = ClangParser::instance()->createTUParser(fd);
+        auto parser { getParserForFile(s.c_str()) };
+        auto fileRoot = parseFile(*parser.get(),fd,s.c_str(),clangParser.get(),true);
+        root->moveToSubEntryAndKeep(fileRoot);
+        processedFiles.insert(s);
+      }
+    }
+  }
+  else // normal processing
 #endif
+  {
+    for (const auto &s : g_inputFiles)
+    {
+      bool ambig;
+      FileDef *fd=findFileDef(Doxygen::inputNameLinkedMap,s.c_str(),ambig);
+      ASSERT(fd!=0);
+      std::unique_ptr<OutlineParserInterface> parser { getParserForFile(s.c_str()) };
+      std::shared_ptr<Entry> fileRoot = parseFile(*parser.get(),fd,s.c_str(),nullptr,true);
+      root->moveToSubEntryAndKeep(fileRoot);
+    }
   }
 }
 
+#endif
+
 // resolves a path that may include symlinks, if a recursive symlink is
 // found an empty string is returned.
 static QCString resolveSymlink(QCString path)
@@ -9707,9 +9811,7 @@ static const char *getArg(int argc,char **argv,int &optind)
 class NullOutlineParser : public OutlineParserInterface
 {
   public:
-    void startTranslationUnit(const char *) {}
-    void finishTranslationUnit() {}
-    void parseInput(const char *, const char *,const std::shared_ptr<Entry> &, bool, QStrList &) {}
+    void parseInput(const char *, const char *,const std::shared_ptr<Entry> &, ClangTUParser*) {}
     bool needsPreprocessing(const QCString &) const { return FALSE; }
     void parsePrototype(const char *) {}
 };
diff --git a/src/filedef.cpp b/src/filedef.cpp
index 08f022b..658023b 100644
--- a/src/filedef.cpp
+++ b/src/filedef.cpp
@@ -82,7 +82,7 @@ class FileDefImpl : public DefinitionImpl, public FileDef
     virtual SDict<Definition> *getUsedClasses() const      { return m_usingDeclList; }
     virtual QList<IncludeInfo> *includeFileList() const    { return m_includeList; }
     virtual QList<IncludeInfo> *includedByFileList() const { return m_includedByList; }
-    virtual void getAllIncludeFilesRecursively(QStrList &incFiles) const;
+    virtual void getAllIncludeFilesRecursively(StringVector &incFiles) const;
     virtual MemberList *getMemberList(MemberListType lt) const;
     virtual const QList<MemberList> &getMemberLists() const { return m_memberLists; }
     virtual MemberGroupSDict *getMemberGroupSDict() const { return m_memberGroupSDict; }
@@ -101,10 +101,8 @@ class FileDefImpl : public DefinitionImpl, public FileDef
     virtual void writeQuickMemberLinks(OutputList &ol,const MemberDef *currentMd) const;
     virtual void writeSummaryLinks(OutputList &ol) const;
     virtual void writeTagFile(FTextStream &t);
-    virtual void startParsing();
-    virtual void writeSource(OutputList &ol,bool sameTu,QStrList &filesInSameTu);
-    virtual void parseSource(bool sameTu,QStrList &filesInSameTu);
-    virtual void finishParsing();
+    virtual void writeSource(OutputList &ol,ClangTUParser *clangParser);
+    virtual void parseSource(ClangTUParser *clangParser);
     virtual void setDiskName(const QCString &name);
     virtual void insertMember(MemberDef *md);
     virtual void insertClass(ClassDef *cd);
@@ -1151,7 +1149,7 @@ void FileDefImpl::writeQuickMemberLinks(OutputList &ol,const MemberDef *currentM
 }
 
 /*! Write a source listing of this file to the output */
-void FileDefImpl::writeSource(OutputList &ol,bool sameTu,QStrList &filesInSameTu)
+void FileDefImpl::writeSource(OutputList &ol,ClangTUParser *clangParser)
 {
   static bool generateTreeView  = Config_getBool(GENERATE_TREEVIEW);
   static bool filterSourceFiles = Config_getBool(FILTER_SOURCE_FILES);
@@ -1209,22 +1207,13 @@ void FileDefImpl::writeSource(OutputList &ol,bool sameTu,QStrList &filesInSameTu
     ol.popGeneratorState();
   }
 
-  (void)sameTu;
-  (void)filesInSameTu;
 #if USE_LIBCLANG
-  if (Doxygen::clangAssistedParsing &&
+  if (Doxygen::clangAssistedParsing && clangParser &&
       (getLanguage()==SrcLangExt_Cpp || getLanguage()==SrcLangExt_ObjC))
   {
     ol.startCodeFragment();
-    if (!sameTu)
-    {
-      ClangParser::instance()->start(absFilePath(),filesInSameTu);
-    }
-    else
-    {
-      ClangParser::instance()->switchToFile(absFilePath());
-    }
-    ClangParser::instance()->writeSources(ol,this);
+    clangParser->switchToFile(this);
+    clangParser->writeSources(ol,this);
     ol.endCodeFragment();
   }
   else
@@ -1268,25 +1257,16 @@ void FileDefImpl::writeSource(OutputList &ol,bool sameTu,QStrList &filesInSameTu
   ol.enableAll();
 }
 
-void FileDefImpl::parseSource(bool sameTu,QStrList &filesInSameTu)
+void FileDefImpl::parseSource(ClangTUParser *clangParser)
 {
   static bool filterSourceFiles = Config_getBool(FILTER_SOURCE_FILES);
   DevNullCodeDocInterface devNullIntf;
-  (void)sameTu;
-  (void)filesInSameTu;
 #if USE_LIBCLANG
-  if (Doxygen::clangAssistedParsing &&
+  if (Doxygen::clangAssistedParsing && clangParser &&
       (getLanguage()==SrcLangExt_Cpp || getLanguage()==SrcLangExt_ObjC))
   {
-    if (!sameTu)
-    {
-      ClangParser::instance()->start(absFilePath(),filesInSameTu);
-    }
-    else
-    {
-      ClangParser::instance()->switchToFile(absFilePath());
-    }
-    ClangParser::instance()->writeSources(devNullIntf,this);
+    clangParser->switchToFile(this);
+    clangParser->writeSources(devNullIntf,this);
   }
   else
 #endif
@@ -1302,15 +1282,6 @@ void FileDefImpl::parseSource(bool sameTu,QStrList &filesInSameTu)
   }
 }
 
-void FileDefImpl::startParsing()
-{
-}
-
-void FileDefImpl::finishParsing()
-{
-  ClangParser::instance()->finish();
-}
-
 void FileDefImpl::addMembersToMemberGroup()
 {
   QListIterator<MemberList> mli(m_memberLists);
@@ -2159,7 +2130,7 @@ bool FileDefImpl::isLinkableInProject() const
 }
 
 static void getAllIncludeFilesRecursively(
-    QDict<void> *filesVisited,const FileDef *fd,QStrList &incFiles)
+    StringUnorderedSet &filesVisited,const FileDef *fd,StringVector &incFiles)
 {
   if (fd->includeFileList())
   {
@@ -2168,21 +2139,21 @@ static void getAllIncludeFilesRecursively(
     for (iii.toFirst();(ii=iii.current());++iii)
     {
       if (ii->fileDef && !ii->fileDef->isReference() &&
-          !filesVisited->find(ii->fileDef->absFilePath()))
+          filesVisited.find(ii->fileDef->absFilePath().str())==filesVisited.end())
       {
         //printf("FileDefImpl::addIncludeDependency(%s)\n",ii->fileDef->absFilePath().data());
-        incFiles.append(ii->fileDef->absFilePath());
-        filesVisited->insert(ii->fileDef->absFilePath(),(void*)0x8);
+        incFiles.push_back(ii->fileDef->absFilePath().str());
+        filesVisited.insert(ii->fileDef->absFilePath().str());
         getAllIncludeFilesRecursively(filesVisited,ii->fileDef,incFiles);
       }
     }
   }
 }
 
-void FileDefImpl::getAllIncludeFilesRecursively(QStrList &incFiles) const
+void FileDefImpl::getAllIncludeFilesRecursively(StringVector &incFiles) const
 {
-  QDict<void> includes(257);
-  ::getAllIncludeFilesRecursively(&includes,this,incFiles);
+  StringUnorderedSet includes;
+  ::getAllIncludeFilesRecursively(includes,this,incFiles);
 }
 
 QCString FileDefImpl::title() const
diff --git a/src/filedef.h b/src/filedef.h
index c03e7ef..e4bb549 100644
--- a/src/filedef.h
+++ b/src/filedef.h
@@ -25,6 +25,7 @@
 #include "definition.h"
 #include "sortdict.h"
 #include "memberlist.h"
+#include "containers.h"
 
 class MemberList;
 class FileDef;
@@ -40,6 +41,7 @@ class MemberGroupSDict;
 class PackageDef;
 class DirDef;
 class FTextStream;
+class ClangTUParser;
 
 /** Class representing the data associated with a \#include statement. */
 struct IncludeInfo
@@ -118,7 +120,7 @@ class FileDef : virtual public Definition
     virtual SDict<Definition> *getUsedClasses() const = 0;
     virtual QList<IncludeInfo> *includeFileList() const = 0;
     virtual QList<IncludeInfo> *includedByFileList() const = 0;
-    virtual void getAllIncludeFilesRecursively(QStrList &incFiles) const = 0;
+    virtual void getAllIncludeFilesRecursively(StringVector &incFiles) const = 0;
 
     virtual MemberList *getMemberList(MemberListType lt) const = 0;
     virtual const QList<MemberList> &getMemberLists() const = 0;
@@ -148,10 +150,8 @@ class FileDef : virtual public Definition
     virtual void writeSummaryLinks(OutputList &ol) const = 0;
     virtual void writeTagFile(FTextStream &t) = 0;
 
-    virtual void startParsing() = 0;
-    virtual void writeSource(OutputList &ol,bool sameTu,QStrList &filesInSameTu) = 0;
-    virtual void parseSource(bool sameTu,QStrList &filesInSameTu) = 0;
-    virtual void finishParsing() = 0;
+    virtual void writeSource(OutputList &ol,ClangTUParser *clangParser) = 0;
+    virtual void parseSource(ClangTUParser *clangParser) = 0;
     virtual void setDiskName(const QCString &name) = 0;
 
     virtual void insertMember(MemberDef *md) = 0;
diff --git a/src/fortranscanner.h b/src/fortranscanner.h
index 6ffcb1f..0e67bb2 100644
--- a/src/fortranscanner.h
+++ b/src/fortranscanner.h
@@ -1,12 +1,12 @@
 /******************************************************************************
  *
- * 
+ *
  *
  * Copyright (C) 1997-2015 by Dimitri van Heesch.
  *
  * Permission to use, copy, modify, and distribute this software and its
- * documentation under the terms of the GNU General Public License is hereby 
- * granted. No representations are made about the suitability of this software 
+ * documentation under the terms of the GNU General Public License is hereby
+ * granted. No representations are made about the suitability of this software
  * for any purpose. It is provided "as is" without express or implied warranty.
  * See the GNU General Public License for more details.
  *
@@ -29,13 +29,10 @@ class FortranOutlineParser : public OutlineParserInterface
   public:
     FortranOutlineParser(FortranFormat format=FortranFormat_Unknown);
    ~FortranOutlineParser();
-    void startTranslationUnit(const char *) {}
-    void finishTranslationUnit() {}
     void parseInput(const char *fileName,
                     const char *fileBuf,
                     const std::shared_ptr<Entry> &root,
-                    bool sameTranslationUnit,
-                    QStrList &filesInSameTranslationUnit);
+                    ClangTUParser *clangParser);
     bool needsPreprocessing(const QCString &extension) const;
     void parsePrototype(const char *text);
 
diff --git a/src/fortranscanner.l b/src/fortranscanner.l
index 195293f..9714602 100644
--- a/src/fortranscanner.l
+++ b/src/fortranscanner.l
@@ -2803,8 +2803,7 @@ FortranOutlineParser::~FortranOutlineParser()
 void FortranOutlineParser::parseInput(const char *fileName,
                                         const char *fileBuf,
                                         const std::shared_ptr<Entry> &root,
-                                        bool /*sameTranslationUnit*/,
-                                        QStrList & /*filesInSameTranslationUnit*/)
+                                        ClangTUParser * /*clangParser*/)
 {
   struct yyguts_t *yyg = (struct yyguts_t*)p->yyscanner;
   yyextra->thisParser = this;
diff --git a/src/markdown.cpp b/src/markdown.cpp
index 583ad17..1a96d45 100644
--- a/src/markdown.cpp
+++ b/src/markdown.cpp
@@ -2528,8 +2528,7 @@ MarkdownOutlineParser::~MarkdownOutlineParser()
 void MarkdownOutlineParser::parseInput(const char *fileName,
                 const char *fileBuf,
                 const std::shared_ptr<Entry> &root,
-                bool /*sameTranslationUnit*/,
-                QStrList & /*filesInSameTranslationUnit*/)
+                ClangTUParser* /*clangParser*/)
 {
   std::shared_ptr<Entry> current = std::make_shared<Entry>();
   current->lang = SrcLangExt_Markdown;
diff --git a/src/markdown.h b/src/markdown.h
index 6ac59cb..43a17cc 100644
--- a/src/markdown.h
+++ b/src/markdown.h
@@ -93,13 +93,10 @@ class MarkdownOutlineParser : public OutlineParserInterface
   public:
     MarkdownOutlineParser();
     virtual ~MarkdownOutlineParser();
-    void startTranslationUnit(const char *) {}
-    void finishTranslationUnit() {}
     void parseInput(const char *fileName,
                     const char *fileBuf,
                     const std::shared_ptr<Entry> &root,
-                    bool sameTranslationUnit,
-                    QStrList &filesInSameTranslationUnit);
+                    ClangTUParser *clangParser);
     bool needsPreprocessing(const QCString &) const { return FALSE; }
     void parsePrototype(const char *text);
   private:
diff --git a/src/parserintf.h b/src/parserintf.h
index f11352e..911b707 100644
--- a/src/parserintf.h
+++ b/src/parserintf.h
@@ -26,12 +26,14 @@
 #include <string>
 
 #include "types.h"
+#include "containers.h"
 
 class Entry;
 class FileDef;
 class CodeOutputInterface;
 class MemberDef;
 class Definition;
+class ClangTUParser;
 
 /** \brief Abstract interface for outline parsers.
  *
@@ -44,36 +46,18 @@ class OutlineParserInterface
   public:
     virtual ~OutlineParserInterface() {}
 
-    /** Starts processing a translation unit (source files + headers).
-     *  After this call parseInput() is called with sameTranslationUnit
-     *  set to FALSE. If parseInput() returns additional include files,
-     *  these are also processed using parseInput() with
-     *  sameTranslationUnit set to TRUE. After that
-     *  finishTranslationUnit() is called.
-     */
-    virtual void startTranslationUnit(const char *fileName) = 0;
-
-    /** Called after all files in a translation unit have been
-     *  processed.
-     */
-    virtual void finishTranslationUnit() = 0;
-
     /** Parses a single input file with the goal to build an Entry tree.
      *  @param[in] fileName    The full name of the file.
      *  @param[in] fileBuf     The contents of the file (zero terminated).
      *  @param[in,out] root    The root of the tree of Entry *nodes
      *             representing the information extracted from the file.
-     *  @param[in] sameTranslationUnit TRUE if this file was found in the same
-     *             translation unit (in the filesInSameTranslationUnit list
-     *             returned for another file).
-     *  @param[in,out] filesInSameTranslationUnit other files expected to be
-     *              found in the same translation unit (used for libclang)
+     *  @param[in] clangParser The clang translation unit parser object
+     *                         or nullptr if disabled.
      */
     virtual void parseInput(const char *fileName,
                             const char *fileBuf,
                             const std::shared_ptr<Entry> &root,
-                            bool sameTranslationUnit,
-                            QStrList &filesInSameTranslationUnit) = 0;
+                            ClangTUParser *clangParser) = 0;
 
     /** Returns TRUE if the language identified by \a extension needs
      *  the C preprocessor to be run before feed the result to the input
diff --git a/src/pyscanner.h b/src/pyscanner.h
index d6e8672..4f0ae38 100644
--- a/src/pyscanner.h
+++ b/src/pyscanner.h
@@ -1,12 +1,12 @@
 /******************************************************************************
  *
- * 
+ *
  *
  * Copyright (C) 1997-2015 by Dimitri van Heesch.
  *
  * Permission to use, copy, modify, and distribute this software and its
- * documentation under the terms of the GNU General Public License is hereby 
- * granted. No representations are made about the suitability of this software 
+ * documentation under the terms of the GNU General Public License is hereby
+ * granted. No representations are made about the suitability of this software
  * for any purpose. It is provided "as is" without express or implied warranty.
  * See the GNU General Public License for more details.
  *
@@ -36,13 +36,10 @@ class PythonOutlineParser : public OutlineParserInterface
   public:
     PythonOutlineParser();
     virtual ~PythonOutlineParser();
-    void startTranslationUnit(const char *) {}
-    void finishTranslationUnit() {}
-    void parseInput(const char * fileName, 
-                    const char *fileBuf, 
+    void parseInput(const char * fileName,
+                    const char *fileBuf,
                     const std::shared_ptr<Entry> &root,
-                    bool sameTranslationUnit,
-                    QStrList &filesInSameTranslationUnit);
+                    ClangTUParser *clangParser);
     bool needsPreprocessing(const QCString &extension) const;
     void parsePrototype(const char *text);
   private:
diff --git a/src/pyscanner.l b/src/pyscanner.l
index a3dbaba..07b39d6 100644
--- a/src/pyscanner.l
+++ b/src/pyscanner.l
@@ -1517,7 +1517,7 @@ static void newFunction(yyscan_t yyscanner)
 static inline int computeIndent(const char *s)
 {
   int col=0;
-  static int tabSize=Config_getInt(TAB_SIZE);
+  int tabSize=Config_getInt(TAB_SIZE);
   const char *p=s;
   char c;
   while ((c=*p++))
@@ -1936,8 +1936,7 @@ PythonOutlineParser::~PythonOutlineParser()
 void PythonOutlineParser::parseInput(const char *fileName,
                                        const char *fileBuf,
                                        const std::shared_ptr<Entry> &root,
-                                       bool /*sameTranslationUnit*/,
-                                       QStrList & /*filesInSameTranslationUnit*/)
+                                       ClangTUParser * /*clangParser*/)
 {
   struct yyguts_t *yyg = (struct yyguts_t*)p->yyscanner;
   yyextra->thisParser = this;
diff --git a/src/scanner.h b/src/scanner.h
index 70df660..cefc934 100644
--- a/src/scanner.h
+++ b/src/scanner.h
@@ -1,12 +1,12 @@
 /******************************************************************************
  *
- * 
+ *
  *
  * Copyright (C) 1997-2015 by Dimitri van Heesch.
  *
  * Permission to use, copy, modify, and distribute this software and its
- * documentation under the terms of the GNU General Public License is hereby 
- * granted. No representations are made about the suitability of this software 
+ * documentation under the terms of the GNU General Public License is hereby
+ * granted. No representations are made about the suitability of this software
  * for any purpose. It is provided "as is" without express or implied warranty.
  * See the GNU General Public License for more details.
  *
@@ -23,7 +23,7 @@
 /** \brief C-like language parser using state-based lexical scanning.
  *
  *  This is the language parser for doxygen. It is somewhat fuzzy and
- *  supports C++ and various languages that are closely related to C++, 
+ *  supports C++ and various languages that are closely related to C++,
  *  such as C, C#, Objective-C, Java, PHP, and IDL.
  */
 class COutlineParser : public OutlineParserInterface
@@ -31,13 +31,10 @@ class COutlineParser : public OutlineParserInterface
   public:
     COutlineParser();
     virtual ~COutlineParser();
-    void startTranslationUnit(const char *fileName);
-    void finishTranslationUnit();
     void parseInput(const char *fileName,
                     const char *fileBuf,
                     const std::shared_ptr<Entry> &root,
-                    bool sameTranslationUnit,
-                    QStrList &filesInSameTranslationUnit);
+                    ClangTUParser *clangParser);
     bool needsPreprocessing(const QCString &extension) const;
     void parsePrototype(const char *text);
   private:
diff --git a/src/scanner.l b/src/scanner.l
index d26a9b2..d9ad41c 100644
--- a/src/scanner.l
+++ b/src/scanner.l
@@ -193,6 +193,8 @@ struct scannerYY_state
   uint             fencedSize = 0;
   bool             nestedComment = false;
   std::vector< std::pair<Entry*,std::shared_ptr<Entry> > > outerScopeEntries;
+
+  ClangTUParser * clangParser = 0;
 };
 
 #if USE_STATE2STRING
@@ -766,9 +768,9 @@ OPERATOR  "operator"{B}*({ARITHOP}|{ASSIGNOP}|{LOGICOP}|{BITOP})
 					    yyextra->current->type = "id";
 					  }
 					  yyextra->current->name = yytext;
-                                          if (yyextra->insideCpp || yyextra->insideObjC) 
+                                          if (yyextra->clangParser && (yyextra->insideCpp || yyextra->insideObjC))
                                           {
-                                            yyextra->current->id = ClangParser::instance()->lookup(yyextra->yyLineNr,yytext);
+                                            yyextra->current->id = yyextra->clangParser->lookup(yyextra->yyLineNr,yytext);
                                           }
   					}
 <ObjCMethod>":"{B}*			{ // start of parameter list
@@ -2045,9 +2047,9 @@ OPERATOR  "operator"{B}*({ARITHOP}|{ASSIGNOP}|{LOGICOP}|{BITOP})
 				          BEGIN(FindMembers);
 			 	        }
 <FindMembers,FindMemberName>{SCOPENAME}	{
-                                          if (Doxygen::clangAssistedParsing && (yyextra->insideCpp || yyextra->insideObjC))
+                                          if (yyextra->clangParser && (yyextra->insideCpp || yyextra->insideObjC))
                                           {
-                                            yyextra->current->id = ClangParser::instance()->lookup(yyextra->yyLineNr,yytext);
+                                            yyextra->current->id = yyextra->clangParser->lookup(yyextra->yyLineNr,yytext);
                                           }
 					  yyextra->yyBegColNr=yyextra->yyColNr;
 					  yyextra->yyBegLineNr=yyextra->yyLineNr;
@@ -2348,9 +2350,9 @@ OPERATOR  "operator"{B}*({ARITHOP}|{ASSIGNOP}|{LOGICOP}|{BITOP})
   */
 <Define>{ID}				{
   					  //printf("Define '%s' without args\n",yytext);
-                                          if (Doxygen::clangAssistedParsing && (yyextra->insideCpp || yyextra->insideObjC))
+                                          if (yyextra->clangParser && (yyextra->insideCpp || yyextra->insideObjC))
                                           {
-                                            yyextra->current->id = ClangParser::instance()->lookup(yyextra->yyLineNr,yytext);
+                                            yyextra->current->id = yyextra->clangParser->lookup(yyextra->yyLineNr,yytext);
                                           }
   					  yyextra->current->bodyLine = yyextra->yyLineNr;
 					  yyextra->current->bodyColumn = yyextra->yyColNr;
@@ -3463,9 +3465,9 @@ OPERATOR  "operator"{B}*({ARITHOP}|{ASSIGNOP}|{LOGICOP}|{BITOP})
 					}
 <Sharp>.				{ yyextra->current->type += *yytext ; }
 <FindFields>{ID}			{
-                                          if (Doxygen::clangAssistedParsing && (yyextra->insideCpp || yyextra->insideObjC))
+                                          if (yyextra->clangParser && (yyextra->insideCpp || yyextra->insideObjC))
                                           {
-                                            yyextra->current->id = ClangParser::instance()->lookup(yyextra->yyLineNr,yytext);
+                                            yyextra->current->id = yyextra->clangParser->lookup(yyextra->yyLineNr,yytext);
                                           }
   					  yyextra->current->bodyLine = yyextra->yyLineNr;
 					  yyextra->current->bodyColumn = yyextra->yyColNr;
@@ -5334,9 +5336,9 @@ OPERATOR  "operator"{B}*({ARITHOP}|{ASSIGNOP}|{LOGICOP}|{BITOP})
   					}
 <CompoundName>{SCOPENAME}		{ 
 					  yyextra->current->name = yytext ;
-                                          if (Doxygen::clangAssistedParsing && (yyextra->insideCpp || yyextra->insideObjC))
+                                          if (yyextra->clangParser && (yyextra->insideCpp || yyextra->insideObjC))
                                           {
-                                            yyextra->current->id = ClangParser::instance()->lookup(yyextra->yyLineNr,yytext);
+                                            yyextra->current->id = yyextra->clangParser->lookup(yyextra->yyLineNr,yytext);
                                           }
 					  lineCount(yyscanner);
 					  if (yyextra->current->spec & Entry::Protocol)
@@ -5399,9 +5401,9 @@ OPERATOR  "operator"{B}*({ARITHOP}|{ASSIGNOP}|{LOGICOP}|{BITOP})
 					  }
 					}
 <ClassVar>{ID}				{
-                                          if (Doxygen::clangAssistedParsing && (yyextra->insideCpp || yyextra->insideObjC))
+                                          if (yyextra->clangParser && (yyextra->insideCpp || yyextra->insideObjC))
                                           {
-                                            yyextra->current->id = ClangParser::instance()->lookup(yyextra->yyLineNr,yytext);
+                                            yyextra->current->id = yyextra->clangParser->lookup(yyextra->yyLineNr,yytext);
                                           }
   					  if (yyextra->insideIDL && qstrcmp(yytext,"switch")==0)
 					  {
@@ -7232,8 +7234,7 @@ static void parseMain(yyscan_t yyscanner,
                       const char *fileName,
                       const char *fileBuf,
                       const std::shared_ptr<Entry> &rt,
-                      bool sameTranslationUnit,
-                      QStrList & filesInSameTranslationUnit)
+                      ClangTUParser *clangParser)
 {
   struct yyguts_t *yyg = (struct yyguts_t*)yyscanner;
   initParser(yyscanner);
@@ -7254,18 +7255,8 @@ static void parseMain(yyscan_t yyscanner,
   yyextra->yyBegLineNr   = 1;
   yyextra->yyBegColNr    = 0;
   yyextra->yyFileName = fileName;
+  yyextra->clangParser = clangParser;
   setContext(yyscanner);
-  if (Doxygen::clangAssistedParsing && (yyextra->insideCpp || yyextra->insideObjC))
-  {
-    if (!sameTranslationUnit) // new file
-    {
-      ClangParser::instance()->start(fileName,filesInSameTranslationUnit);
-    }
-    else
-    {
-      ClangParser::instance()->switchToFile(fileName);
-    }
-  }
   rt->lang = yyextra->language;
   msg("Parsing file %s...\n",yyextra->yyFileName.data());
 
@@ -7402,33 +7393,17 @@ COutlineParser::~COutlineParser()
   scannerYYlex_destroy(p->yyscanner);
 }
 
-void COutlineParser::startTranslationUnit(const char *)
-{
-}
-
-void COutlineParser::finishTranslationUnit()
-{
-  struct yyguts_t *yyg = (struct yyguts_t*)p->yyscanner;
-  bool processWithClang = yyextra->insideCpp || yyextra->insideObjC;
-  if (processWithClang)
-  {
-    ClangParser::instance()->finish();
-  }
-}
-
 void COutlineParser::parseInput(const char *fileName,
                                   const char *fileBuf,
                                   const std::shared_ptr<Entry> &root,
-                                  bool sameTranslationUnit,
-                                  QStrList & filesInSameTranslationUnit)
+                                  ClangTUParser *clangParser)
 {
   struct yyguts_t *yyg = (struct yyguts_t*)p->yyscanner;
   yyextra->thisParser = this;
 
   printlex(yy_flex_debug, TRUE, __FILE__, fileName);
 
-  ::parseMain(p->yyscanner, fileName,fileBuf,root,
-              sameTranslationUnit,filesInSameTranslationUnit);
+  ::parseMain(p->yyscanner,fileName,fileBuf,root,clangParser);
 
   printlex(yy_flex_debug, FALSE, __FILE__, fileName);
 }
diff --git a/src/vhdldocgen.cpp b/src/vhdldocgen.cpp
index 28a2028..5cc57ec 100644
--- a/src/vhdldocgen.cpp
+++ b/src/vhdldocgen.cpp
@@ -2942,10 +2942,8 @@ void VhdlDocGen::createFlowChart(const MemberDef *mdef)
   auto parser { Doxygen::parserManager->getOutlineParser(".vhd") };
   VhdlDocGen::setFlowMember(mdef);
   std::shared_ptr<Entry> root = std::make_shared<Entry>();
-  QStrList filesInSameTu;
-  parser->startTranslationUnit("");
-  parser->parseInput("",codeFragment.data(),root,FALSE,filesInSameTu);
-  parser->finishTranslationUnit();
+  StringVector filesInSameTu;
+  parser->parseInput("",codeFragment.data(),root,nullptr);
 }
 
 void VhdlDocGen::resetCodeVhdlParserState()
diff --git a/src/vhdljjparser.cpp b/src/vhdljjparser.cpp
index aa566ae..9ad9e23 100644
--- a/src/vhdljjparser.cpp
+++ b/src/vhdljjparser.cpp
@@ -126,7 +126,7 @@ VHDLOutlineParser::~VHDLOutlineParser()
 }
 
 void VHDLOutlineParser::parseInput(const char *fileName,const char *fileBuf,
-                                   const std::shared_ptr<Entry> &root, bool ,QStrList&)
+                                   const std::shared_ptr<Entry> &root, ClangTUParser *)
 {
   VhdlParser::SharedState *s = &p->shared;
   p->thisParser=this;
diff --git a/src/vhdljjparser.h b/src/vhdljjparser.h
index 940631d..651221c 100755
--- a/src/vhdljjparser.h
+++ b/src/vhdljjparser.h
@@ -32,20 +32,17 @@ class VHDLOutlineParser : public OutlineParserInterface
   public:
     VHDLOutlineParser();
     virtual ~VHDLOutlineParser();
-    void startTranslationUnit(const char *) {}
-    void finishTranslationUnit() {}
     void parseInput(const char * fileName,
                     const char *fileBuf,
                     const std::shared_ptr<Entry> &root,
-                    bool sameTranslationUnit,
-                    QStrList &filesInSameTranslationUnit);
+                    ClangTUParser *clangParser);
 
     bool needsPreprocessing(const QCString &) const { return TRUE; }
     void parsePrototype(const char *text);
 
 
     // interface for generated parser code
-   
+
     void setLineParsed(int tok);
     int getLine(int tok);
     int getLine();