pdf preview generation: Use QtConcurrent::mapped + QFutureWatcher instead of own single-thread solution

cli/cli.pro

@@ -50,7 +50,6 @@ HEADERS += \
     commanddelete.h \
     commandupdate.h \
     filesaver.h \
-    filedata.h \
     databasefactory.h \
     sqlitedbservice.h \
     logger.h \

gui/gui.pro

@@ -4,7 +4,7 @@
 #
 #-------------------------------------------------
 
-QT       += core gui
+QT       += core concurrent gui
 
 greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
 CONFIG += c++14

gui/mainwindow.cpp

@@ -26,9 +26,6 @@ MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWi
 		qDebug() << "failed to open database";
 		throw std::runtime_error("Failed to open database");
 	}
-
-	pdfWorker = new PdfWorker();
-	pdfWorker->moveToThread(&pdfWorkerThread);
 	connectSignals();
 	searchThread.start();
 	ui->treeResultsList->setContextMenuPolicy(Qt::ContextMenuPolicy::CustomContextMenu);
@@ -51,15 +48,19 @@ void MainWindow::connectSignals()
 				auto results = searchWatcher.future().result();
 				handleSearchResults(results);
 			});
+
+	connect(&pdfWorkerWatcher, &QFutureWatcher<PdfPreview>::resultReadyAt, this,
+			[&](int index) { pdfPreviewReceived(pdfWorkerWatcher.resultAt(index)); });
+
+	connect(&pdfWorkerWatcher, &QFutureWatcher<PdfPreview>::progressValueChanged, ui->pdfProcessBar,
+			&QProgressBar::setValue);
+
 	// connect(searchWorker, &SearchWorker::searchCancelled, this, &MainWindow::handleCancelledSearch);
 	//  connect(searchWorker, &SearchWorker::searchError, this, &MainWindow::handleSearchError);
 	connect(ui->treeResultsList, &QTreeWidget::itemActivated, this, &MainWindow::treeSearchItemActivated);
 	connect(ui->treeResultsList, &QTreeWidget::customContextMenuRequested, this,
 			&MainWindow::showSearchResultsContextMenu);
 	connect(ui->tabWidget, &QTabWidget::currentChanged, this, &MainWindow::tabChanged);
-	connect(this, &MainWindow::startPdfPreviewGeneration, pdfWorker, &PdfWorker::generatePreviews);
-	connect(pdfWorker, &PdfWorker::previewReady, this, &MainWindow::pdfPreviewReceived);
-	connect(pdfWorker, &PdfWorker::previewsFinished, [&] { this->pdfDirty = false; });
 	connect(ui->comboScale, qOverload<const QString &>(&QComboBox::currentIndexChanged), this,
 			&MainWindow::comboScaleChanged);
 }
@@ -117,8 +118,6 @@ void MainWindow::pdfPreviewReceived(PdfPreview preview)
 	ClickLabel *label = new ClickLabel();
 	label->setPixmap(QPixmap::fromImage(preview.previewImage));
 	ui->scrollAreaWidgetContents->layout()->addWidget(label);
-	ui->pdfProcessBar->setValue(++processedPdfPreviews);
-
 	connect(label, &ClickLabel::clicked,
 			[=]()
 			{
@@ -199,11 +198,12 @@ void MainWindow::handleSearchResults(const QVector<SearchResult> &results)
 
 void MainWindow::makePdfPreview()
 {
-	if(!pdfWorkerThread.isRunning())
-		pdfWorkerThread.start();
 
-	pdfWorker->cancelAndWait();
-	QCoreApplication::processEvents(); // Process not processed images
+	this->pdfWorkerWatcher.cancel();
+	this->pdfWorkerWatcher.waitForFinished();
+
+	QCoreApplication::processEvents(); // Maybe not necessary anymore, depends on whether it's possible that a slot is
+									   // still to be fired.
 	qDeleteAll(ui->scrollAreaWidgetContents->children());
 
 	ui->scrollAreaWidgetContents->setLayout(new QHBoxLayout());
@@ -211,8 +211,10 @@ void MainWindow::makePdfPreview()
 	processedPdfPreviews = 0;
 	QString scaleText = ui->comboScale->currentText();
 	scaleText.chop(1);
-
-	emit startPdfPreviewGeneration(this->pdfSearchResults, scaleText.toInt() / 100.);
+	PdfWorker worker;
+	this->pdfWorkerWatcher.setFuture(worker.generatePreviews(this->pdfSearchResults, scaleText.toInt() / 100.));
+	ui->pdfProcessBar->setMaximum(this->pdfWorkerWatcher.progressMaximum());
+	ui->pdfProcessBar->setMinimum(this->pdfWorkerWatcher.progressMinimum());
 }
 
 void MainWindow::handleCancelledSearch()

gui/mainwindow.h

@@ -32,7 +32,7 @@ class MainWindow : public QMainWindow
 	QSqlDatabase db;
 	QFuture<QVector<SearchResult>> searchFuture;
 	QFutureWatcher<QVector<SearchResult>> searchWatcher;
-	PdfWorker *pdfWorker;
+	QFutureWatcher<PdfPreview> pdfWorkerWatcher;
 	void add(QString path, unsigned int page);
 	QThread searchThread;
 	QThread pdfWorkerThread;

gui/pdfworker.cpp

@@ -3,16 +3,28 @@
 #include <QScreen>
 #include <QDebug>
 #include <QScopedPointer>
+#include <QMutexLocker>
+#include <QtConcurrent/QtConcurrent>
+#include <QtConcurrent/QtConcurrentMap>
 #include "pdfworker.h"
 
-PdfWorker::PdfWorker()
+static QMutex cacheMutex;
+struct Renderer
 {
-}
 
-Poppler::Document *PdfWorker::document(QString path)
+	typedef PdfPreview result_type;
+	double scaleX;
+	double scaleY;
+	QHash<QString, Poppler::Document *> documentcache;
+	Renderer(double scaleX, double scaleY)
 	{
-	if(this->documentcache.contains(path))
-		return this->documentcache.value(path);
+		this->scaleX = scaleX;
+		this->scaleY = scaleY;
+	}
+	Poppler::Document *document(QString path)
+	{
+		if(documentcache.contains(path))
+			return documentcache.value(path);
 
 		Poppler::Document *result = Poppler::Document::load(path);
 		if(result == nullptr)
@@ -20,60 +32,51 @@ Poppler::Document *PdfWorker::document(QString path)
 			return nullptr;
 		}
 		result->setRenderHint(Poppler::Document::TextAntialiasing);
-	this->documentcache.insert(path, result);
+		QMutexLocker locker(&cacheMutex);
+		documentcache.insert(path, result);
 		return result;
 	}
-void PdfWorker::generatePreviews(QVector<SearchResult> paths, double scalefactor)
+
+	PdfPreview operator()(const PdfPreview &preview)
 	{
-	this->cancelCurrent = false;
-	this->generating = true;
-	for(SearchResult &sr : paths)
-	{
-		if(this->cancelCurrent.load())
-		{
-			break;
-		}
-		Poppler::Document *doc = document(sr.fileData.absPath);
+		Poppler::Document *doc = document(preview.documentPath);
 		if(doc == nullptr)
 		{
-			continue;
+			return preview;
 		}
 		if(doc->isLocked())
 		{
-			continue;
+			return preview;
 		}
-		for(unsigned int page : sr.pages)
-		{
-			int p = (int)page - 1;
+		int p = (int)preview.page - 1;
 		if(p < 0)
+		{
 			p = 0;
+		}
 		Poppler::Page *pdfPage = doc->page(p);
-			QImage image =
-				pdfPage->renderToImage(QGuiApplication::primaryScreen()->physicalDotsPerInchX() * scalefactor,
-									   QGuiApplication::primaryScreen()->physicalDotsPerInchY() * scalefactor);
+		PdfPreview result = preview;
+		result.previewImage = pdfPage->renderToImage(scaleX, scaleY);
+		return result;
+	}
+};
 
-			PdfPreview preview;
-			preview.previewImage = image;
-			preview.documentPath = sr.fileData.absPath;
-			preview.page = page;
-			emit previewReady(preview);
-		}
-	}
-	isFreeMutex.lock();
-	isFree.wakeOne();
-	isFreeMutex.unlock();
-	generating = false;
-	emit previewsFinished();
-}
-
-void PdfWorker::cancelAndWait()
+QFuture<PdfPreview> PdfWorker::generatePreviews(QVector<SearchResult> paths, double scalefactor)
 {
-	if(this->generating.load())
-	{
-		this->cancelCurrent = true;
+	QVector<PdfPreview> previews;
 
-		isFreeMutex.lock();
-		isFree.wait(&isFreeMutex);
-		isFreeMutex.unlock();
+	for(SearchResult &sr : paths)
+	{
+		for(int page : sr.pages)
+		{
+			PdfPreview p;
+			p.documentPath = sr.fileData.absPath;
+			p.page = page;
+			previews.append(p);
 		}
 	}
+
+	double scaleX = QGuiApplication::primaryScreen()->physicalDotsPerInchX() * scalefactor;
+	double scaleY = QGuiApplication::primaryScreen()->physicalDotsPerInchY() * scalefactor;
+
+	return QtConcurrent::mapped(previews, Renderer(scaleX, scaleY));
+}

gui/pdfworker.h

@@ -6,29 +6,17 @@
 #include <QThread>
 #include <QMutex>
 #include <QWaitCondition>
+#include <QMutex>
+#include <QFuture>
 #include <poppler-qt5.h>
 #include "pdfpreview.h"
 #include "searchresult.h"
+
 class PdfWorker : public QObject
 {
 	Q_OBJECT
-
-  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:
-	void previewReady(PdfPreview p);
-	void previewsFinished();
+	QFuture<PdfPreview> generatePreviews(QVector<SearchResult> paths, double scalefactor);
 };
 
 #endif // PDFWORKER_H