Wait till pdfworker finishes before new search, cancel running

gui/pdfworker.h

@@ -3,6 +3,9 @@
 #include <QObject>
 #include <QImage>
 #include <QHash>
+#include <QThread>
+#include <QMutex>
+#include <QWaitCondition>
 #include <poppler-qt5.h>
 #include "pdfpreview.h"
 #include "searchresult.h"
@@ -13,9 +16,14 @@ class PdfWorker : public QObject
   private:
 	QHash<QString, Poppler::Document *> documentcache;
 	Poppler::Document *document(QString path);
+	std::atomic<bool> cancelCurrent{false};
+	std::atomic<bool> generating{false};
+	QMutex isFreeMutex;
+	QWaitCondition isFree;
 
   public:
 	PdfWorker();
+	void cancelAndWait();
   public slots:
 	void generatePreviews(QVector<SearchResult> paths, double scalefactor);
   signals: