Merge pull request #4381 from dmitrio95/276235-2.X-system-staff-text-2

fix #276235: make it possible to enable readahead for XmlReader

libmscore/read206.cpp

@@ -2949,26 +2949,24 @@ static void readMeasure(Measure* m, int staffIdx, XmlReader& e)
                   // MuseScore 3 has different types for system text and
                   // staff text while MuseScore 2 didn't.
                   // We need to decide first which one we should create.
-                  QIODevice* dev = e.device();
                   QString styleName;
-                  if (dev && !dev->isSequential()) { // we want to be able to seek a position
-                        const auto pos = dev->pos();
-                        dev->seek(e.characterOffset());
-                        const QString closeTag = QString("</").append(tag).append(">");
-                        QByteArray arrLine = dev->readLine();
-                        while (!arrLine.isEmpty()) {
-                              QString line(arrLine);
-                              if (line.contains("<style>")) {
-                                    QRegExp re("<style>([A-z0-9]+)</style>");
-                                    if (re.indexIn(line) > -1)
-                                          styleName = re.cap(1);
-                                    break;
+                  if (e.readAheadAvailable()) {
+                        e.performReadAhead([&styleName, tag](QIODevice& dev) {
+                              const QString closeTag = QString("</").append(tag).append(">");
+                              QByteArray arrLine = dev.readLine();
+                              while (!arrLine.isEmpty()) {
+                                    QString line(arrLine);
+                                    if (line.contains("<style>")) {
+                                          QRegExp re("<style>([A-z0-9]+)</style>");
+                                          if (re.indexIn(line) > -1)
+                                                styleName = re.cap(1);
+                                          return;
+                                          }
+                                    if (line.contains(closeTag))
+                                          return;
+                                    arrLine = dev.readLine();
                                     }
-                              if (line.contains(closeTag))
-                                    break;
-                              arrLine = dev->readLine();
-                              }
-                        dev->seek(pos);
+                              });
                         }
                   StaffTextBase* t;
                   if (styleName == "System"   || styleName == "Tempo"

libmscore/scorefile.cpp

@@ -816,6 +816,8 @@ Score::FileError MasterScore::loadCompressedMsc(QIODevice* io, bool ignoreVersio
                   }
             }
       XmlReader e(dbuf);
+      QBuffer readAheadBuf(&dbuf);
+      e.setReadAheadDevice(&readAheadBuf);
       e.setDocName(masterScore()->fileInfo()->completeBaseName());
 
       FileError retval = read1(e, ignoreVersionError);
@@ -873,6 +875,7 @@ Score::FileError MasterScore::loadMsc(QString name, QIODevice* io, bool ignoreVe
             return loadCompressedMsc(io, ignoreVersionError);
       else {
             XmlReader r(io);
+            r.setReadAheadDevice(io);
             return read1(r, ignoreVersionError);
             }
       }

libmscore/xml.h

@@ -67,6 +67,10 @@ class LinksIndexer {
 class XmlReader : public QXmlStreamReader {
       QString docName;  // used for error reporting
 
+      // For readahead possibility.
+      // If needed, must be explicitly set by setReadAheadDevice.
+      QIODevice* _readAheadDevice = nullptr;
+
       // Score read context (for read optimizations):
       int _tick             { 0       };
       int _tickOffset       { 0       };
@@ -105,6 +109,7 @@ class XmlReader : public QXmlStreamReader {
       XmlReader(QIODevice* d, const QString& st = QString()) : QXmlStreamReader(d), docName(st) {}
       XmlReader(const QString& d, const QString& st = QString()) : QXmlStreamReader(d), docName(st) {}
       XmlReader(const XmlReader&) = delete;
+      XmlReader& operator=(const XmlReader&) = delete;
       ~XmlReader();
 
       bool hasAccidental;                     // used for userAccidental backward compatibility
@@ -195,6 +200,11 @@ class XmlReader : public QXmlStreamReader {
       Tid addUserTextStyle(const QString& name);
       Tid lookupUserTextStyle(const QString& name);
 
+      // Ownership on read ahead device is NOT transfered to XmlReader.
+      void setReadAheadDevice(QIODevice* dev) { if (!dev->isSequential()) _readAheadDevice = dev; }
+      bool readAheadAvailable() const { return bool(_readAheadDevice); }
+      void performReadAhead(std::function<void(QIODevice&)> readAheadRoutine);
+
       QList<std::pair<Element*, QPointF>>& fixOffsets() { return  _fixOffsets; }
       };
 

libmscore/xmlreader.cpp

@@ -555,6 +555,27 @@ Tid XmlReader::lookupUserTextStyle(const QString& name)
       return Tid::TEXT_STYLES;       // not found
       }
 
+//---------------------------------------------------------
+//   performReadAhead
+//    If f is called, the device will be non-sequential and
+//    open. Reading position equals to the current value of
+//    characterOffset(), but it is possible to seek for any
+//    other position inside f.
+//---------------------------------------------------------
+
+void XmlReader::performReadAhead(std::function<void(QIODevice&)> f)
+      {
+      if (!_readAheadDevice || _readAheadDevice->isSequential())
+            return;
+      if (!_readAheadDevice->isOpen())
+            _readAheadDevice->open(QIODevice::ReadOnly);
+
+      const auto pos = _readAheadDevice->pos();
+      _readAheadDevice->seek(characterOffset());
+      f(*_readAheadDevice);
+      _readAheadDevice->seek(pos);
+      }
+
 //---------------------------------------------------------
 //   addConnectorInfo
 //---------------------------------------------------------