Merge pull request #415 from OpenBoard-org/dev-qt5.1x-pdf_optimize_zoom_only

Made the pdf processing thread be terminated on exit after 3s.

src/pdf/XPDFRenderer.cpp

@@ -106,7 +106,13 @@ XPDFRenderer::~XPDFRenderer()
 {
     disconnect(&m_cacheThread, SIGNAL(finished()), this, SLOT(OnThreadFinished()));
     m_cacheThread.cancelPending();
-    m_cacheThread.wait(); // Would crash if data deleted during processing.
+    m_cacheThread.wait(XPDFThreadMaxTimeoutOnExit::timeout_ms);
+    if (m_cacheThread.isRunning())
+    {
+        // Kill the thread, which might still run for minutes if the user choose a heavy pdf highly zoomed.
+        // Since there is no data written, but only processing, this is safe on a modern OS.
+        m_cacheThread.terminate();
+    }
 
     for(int i = 0; i < m_pdfZoomCache.size(); i++)
     {

src/pdf/XPDFRenderer.h

@@ -67,6 +67,11 @@ namespace XPDFRendererZoomFactor
     const double mode4_zoomFactorIterations = 7;
 }
 
+namespace XPDFThreadMaxTimeoutOnExit
+{
+    const double timeout_ms = 3000;
+}
+
 class XPDFRenderer : public PDFRenderer
 {
     Q_OBJECT