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

@@ -28,9 +28,6 @@ MainWindow::MainWindow(QWidget *parent) :
         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);
@@ -51,14 +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);
 }
 
@@ -114,8 +116,6 @@ 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, [=]() {
         QSettings settings;
         QString command = settings.value("pdfviewer").toString();
@@ -194,11 +194,11 @@ 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());
@@ -206,8 +206,11 @@ void MainWindow::makePdfPreview()
    processedPdfPreviews = 0;
    QString scaleText = ui->comboScale->currentText();
    scaleText.chop(1);
+   PdfWorker worker;
+   this->pdfWorkerWatcher.setFuture(worker.generatePreviews(this->pdfSearchResults, scaleText.toInt() / 100.));
+   ui->pdfProcessBar->setMaximum(this->pdfWorkerWatcher.progressMaximum());
+   ui->pdfProcessBar->setMinimum(this->pdfWorkerWatcher.progressMinimum());
 
-   emit startPdfPreviewGeneration(this->pdfSearchResults, scaleText.toInt() / 100.);
 }
 
 

gui/mainwindow.h

@@ -30,7 +30,7 @@ private:
     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

@@ -3,77 +3,89 @@
 #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)
-{
-    if(this->documentcache.contains(path))
-        return this->documentcache.value(path);
-
-    Poppler::Document *result = Poppler::Document::load(path);
-    if(result == nullptr)
+    typedef PdfPreview result_type;
+    double scaleX;
+    double scaleY;
+    QHash<QString, Poppler::Document *> documentcache;
+    Renderer(double scaleX, double scaleY)
     {
-        return nullptr;
+        this->scaleX = scaleX;
+        this->scaleY = scaleY;
     }
-    result->setRenderHint(Poppler::Document::TextAntialiasing);
-    this->documentcache.insert(path, result);
-    return result;
-}
-void PdfWorker::generatePreviews(QVector<SearchResult> paths, double scalefactor)
-{
-    this->cancelCurrent = false;
-    this->generating = true;
-    for(SearchResult &sr : paths)
+    Poppler::Document *document(QString path)
     {
-        if(this->cancelCurrent.load())
+        if(documentcache.contains(path))
+            return documentcache.value(path);
+
+        Poppler::Document *result = Poppler::Document::load(path);
+        if(result == nullptr)
         {
-            break;
+            return nullptr;
         }
-        Poppler::Document *doc = document(sr.fileData.absPath);
+        result->setRenderHint(Poppler::Document::TextAntialiasing);
+        QMutexLocker locker(&cacheMutex);
+        documentcache.insert(path, result);
+        return result;
+    }
+
+
+
+    PdfPreview operator()(const PdfPreview &preview)
+    {
+        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)preview.page - 1;
+        if(p < 0)
         {
-            int p = (int)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 preview;
-            preview.previewImage = image;
-            preview.documentPath = sr.fileData.absPath;
-            preview.page = page;
-            emit previewReady(preview);
+            p = 0;
         }
-
+        Poppler::Page *pdfPage = doc->page(p);
+        PdfPreview result = preview;
+        result.previewImage  = pdfPage->renderToImage(scaleX, scaleY);
+        return result;
     }
-    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

@@ -6,28 +6,18 @@
 #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