Adjust thread priorities according to discussion in Bug #1270583.

src/analyserqueue.cpp

@@ -421,7 +421,7 @@ AnalyserQueue* AnalyserQueue::createDefaultAnalyserQueue(
     ret->addAnalyser(new AnalyserBeats(pConfig));
     ret->addAnalyser(new AnalyserKey(pConfig));
 
-    ret->start(QThread::IdlePriority);
+    ret->start(QThread::LowPriority);
     return ret;
 }
 
@@ -436,6 +436,6 @@ AnalyserQueue* AnalyserQueue::createAnalysisFeatureAnalyserQueue(
     ret->addAnalyser(new AnalyserBeats(pConfig));
     ret->addAnalyser(new AnalyserKey(pConfig));
 
-    ret->start(QThread::IdlePriority);
+    ret->start(QThread::LowPriority);
     return ret;
 }

src/cachingreader.cpp

@@ -67,7 +67,7 @@ CachingReader::CachingReader(const char* group,
             this, SIGNAL(trackLoadFailed(TrackPointer, QString)),
             Qt::DirectConnection);
 
-    m_pWorker->start();
+    m_pWorker->start(QThread::HighPriority);
 }
 
 

src/engine/enginemaster.cpp

@@ -53,7 +53,7 @@ EngineMaster::EngineMaster(ConfigObject<ConfigValue>* _config,
     m_bBusOutputConnected[1] = false;
     m_bBusOutputConnected[2] = false;
     m_pWorkerScheduler = new EngineWorkerScheduler(this);
-    m_pWorkerScheduler->start();
+    m_pWorkerScheduler->start(QThread::HighPriority);
 
     // Master sample rate
     m_pMasterSampleRate = new ControlObject(ConfigKey(group, "samplerate"), true, true);

src/library/browse/browsethread.cpp

@@ -31,7 +31,7 @@ BrowseThread::BrowseThread(QObject *parent)
     m_bStopThread = false;
     m_model_observer = NULL;
     //start Thread
-    start(QThread::LowestPriority);
+    start(QThread::LowPriority);
 
 }
 

src/library/itunes/itunesfeature.cpp

@@ -323,7 +323,7 @@ void ITunesFeature::guessMusicLibraryMountpoint(QXmlStreamReader &xml) {
 TreeItem* ITunesFeature::importLibrary() {
     //Give thread a low priority
     QThread* thisThread = QThread::currentThread();
-    thisThread->setPriority(QThread::LowestPriority);
+    thisThread->setPriority(QThread::LowPriority);
 
     //Delete all table entries of iTunes feature
     ScopedTransaction transaction(m_database);

src/library/libraryscanner.cpp

@@ -141,9 +141,6 @@ void LibraryScanner::run() {
     QThread::currentThread()->setObjectName(QString("LibraryScanner %1").arg(++id));
     //m_pProgress->slotStartTiming();
 
-    // Lower our priority to help not grind crappy computers.
-    setPriority(QThread::LowPriority);
-
     qRegisterMetaType<QSet<int> >("QSet<int>");
 
     if (!m_database.isValid()) {
@@ -326,7 +323,7 @@ void LibraryScanner::scan(QWidget* parent) {
             this, SLOT(cancel()));
     connect(&m_trackDao, SIGNAL(progressVerifyTracksOutside(QString)),
             m_pProgress, SLOT(slotUpdate(QString)));
-    start();
+    start(QThread::LowPriority);
 }
 
 void LibraryScanner::cancel() {

src/library/traktor/traktorfeature.cpp

@@ -169,7 +169,7 @@ void TraktorFeature::activateChild(const QModelIndex& index) {
 TreeItem* TraktorFeature::importLibrary(QString file) {
     //Give thread a low priority
     QThread* thisThread = QThread::currentThread();
-    thisThread->setPriority(QThread::LowestPriority);
+    thisThread->setPriority(QThread::LowPriority);
     //Invisible root item of Traktor's child model
     TreeItem* root = NULL;
     //Delete all table entries of Traktor feature

src/waveform/waveformwidgetfactory.cpp

@@ -659,7 +659,7 @@ int WaveformWidgetFactory::findIndexOf(WWaveformViewer* viewer) const {
 
 void WaveformWidgetFactory::startVSync(MixxxMainWindow* mixxxMainWindow) {
     m_vsyncThread = new VSyncThread(mixxxMainWindow);
-    m_vsyncThread->start();
+    m_vsyncThread->start(QThread::NormalPriority);
 
     connect(m_vsyncThread, SIGNAL(vsyncRender()),
             this, SLOT(render()));