fix: rewrite atEnd function

take the code from vedgy's webengine port

article_netmgr.cc

@@ -442,6 +442,14 @@ qint64 ArticleResourceReply::bytesAvailable() const
   return avail - alreadyRead + QNetworkReply::bytesAvailable();
 }
 
+bool ArticleResourceReply::atEnd() const
+{
+  // QWebEngineUrlRequestJob finishes and is destroyed as soon as QIODevice::atEnd() returns true.
+  // QNetworkReply::atEnd() returns true while bytesAvailable() returns 0.
+  // Return false if the data request is not finished to work around always-blank web page.
+  return req->isFinished() && QNetworkReply::atEnd();
+}
+
 qint64 ArticleResourceReply::readData( char * out, qint64 maxSize )
 {
   // From the doc: "This function might be called with a maxSize of 0,
@@ -458,6 +466,18 @@ qint64 ArticleResourceReply::readData( char * out, qint64 maxSize )
 
   qint64 left = avail - alreadyRead;
   
+  if(  left == 0 && !finished )
+  {
+    // Work around endlessly repeated useless calls to readData(). The sleep duration is a tradeoff.
+    // On the one hand, lowering the duration reduces CPU usage. On the other hand, overly long
+    // sleep duration reduces page content update frequency in the web view.
+    // Waiting on a condition variable is more complex and actually works worse than
+    // simple fixed-duration sleeping, because the web view is not updated until
+    // the data request is finished if readData() returns only when new data arrives.
+    QThread::msleep( 30 );
+    return 0;
+  }
+
   qint64 toRead = maxSize < left ? maxSize : left;
   GD_DPRINTF( "====reading  %d of (%d) bytes . Finished: %d", (int)toRead, avail, finished );
 

article_netmgr.hh

@@ -148,7 +148,7 @@ public:
 protected:
 
   virtual qint64 bytesAvailable() const;
-
+  bool atEnd() const override;
   virtual void abort()
   {}
   virtual qint64 readData( char * data, qint64 maxSize );

dictionary.cc

@@ -117,7 +117,6 @@ void DataRequest::appendDataSlice( const void * buffer, size_t size ) {
   data.resize( data.size() + size );
 
   memcpy( &data.front() + offset, buffer, size );
-  cond.wakeAll();
 }
 
 void DataRequest::getDataSlice( size_t offset, size_t size, void * buffer )
@@ -130,22 +129,9 @@ void DataRequest::getDataSlice( size_t offset, size_t size, void * buffer )
   if( !hasAnyData )
     throw exSliceOutOfRange();
 
-  while( offset + size > data.size() && !quit ) {
-    cond.wait( &dataMutex,10 );
-  }
-  if(quit)
-    return;
-
   memcpy( buffer, &data[ offset ], size );
 }
 
-DataRequest::~DataRequest()
-{
-  quit = true;
-  cond.wakeAll();
-  finish();
-}
-
 vector< char > & DataRequest::getFullData()
 {
   if ( !isFinished() )

dictionary.hh

@@ -201,18 +201,13 @@ public:
   {
   }
 
-  ~DataRequest();
-
 protected:
 
   // Subclasses should be filling up the 'data' array, locking the mutex when
   // whey work with it.
   Mutex dataMutex;
 
-  QWaitCondition cond;
-
   bool hasAnyData; // With this being false, dataSize() always returns -1
-  bool quit = false;
   vector< char > data;
 };