Avoid that, if an error dialog pops up during a long operation, it freezes LyX.

src/frontends/Application.h

@@ -246,6 +246,8 @@ public:
 	virtual bool longOperationCancelled() = 0;
 	/// Stop the long operation mode (i.e., release the GUI)
 	virtual void stopLongOperation() = 0;
+	/// A started long operation is still in progress ?
+	virtual bool longOperationStarted() = 0;
 
 };
 

src/frontends/qt4/GuiAlert.cpp

@@ -92,6 +92,11 @@ int doPrompt(docstring const & title0, docstring const & question,
 
 	docstring const title = bformat(_("LyX: %1$s"), title0);
 
+	/// Long operation in progress prevents user from Ok-ing the error dialog
+	bool long_op = theApp()->longOperationStarted();
+	if (long_op)
+		theApp()->stopLongOperation();
+
 	// For some reason, sometimes Qt uses a hourglass or watch cursor when
 	// displaying the alert. Hence, we ask for the standard cursor shape.
 	qApp->setOverrideCursor(Qt::ArrowCursor);
@@ -116,6 +121,9 @@ int doPrompt(docstring const & title0, docstring const & question,
 
 	qApp->restoreOverrideCursor();
 
+	if (long_op)
+		theApp()->startLongOperation();
+
 	// Qt bug: can return -1 on cancel or WM close, despite the docs.
 	if (res == -1)
 		res = cancel_button;
@@ -197,6 +205,11 @@ void doError(docstring const & title0, docstring const & message)
 		return;
 	}
 
+	/// Long operation in progress prevents user from Ok-ing the error dialog
+	bool long_op = theApp()->longOperationStarted();
+	if (long_op)
+		theApp()->stopLongOperation();
+
 	// Don't use a hourglass cursor while displaying the alert
 	qApp->setOverrideCursor(Qt::ArrowCursor);
 
@@ -205,6 +218,9 @@ void doError(docstring const & title0, docstring const & message)
 		toqstr(message));
 
 	qApp->restoreOverrideCursor();
+
+	if (long_op)
+		theApp()->startLongOperation();
 }
 
 void error(docstring const & title0, docstring const & message)

src/frontends/qt4/GuiApplication.cpp

@@ -684,6 +684,7 @@ public:
 class KeyChecker : public QObject {
 private:
 	bool pressed_;
+	bool started_;
 public:
 	KeyChecker() {
 		pressed_ = false;
@@ -691,14 +692,19 @@ public:
 	void start() {
 		QCoreApplication::instance()->installEventFilter(this);
 		pressed_ = false;
+		started_ = true;
 	}
 	void stop() {
 		QCoreApplication::instance()->removeEventFilter(this);
+		started_ = false;
 	}
 	bool pressed() {
 		QCoreApplication::processEvents();
 		return pressed_;
 	}
+	bool started() const {
+		return started_;
+	}
 	bool eventFilter(QObject *obj, QEvent *event) {
 		LYXERR(Debug::ACTION, "Event Type: " << event->type());
 		switch (event->type()) {
@@ -2679,6 +2685,11 @@ void GuiApplication::stopLongOperation() {
 }
 
 
+bool GuiApplication::longOperationStarted() {
+	return d->key_checker_.started();
+}
+
+
 ////////////////////////////////////////////////////////////////////////
 //
 // X11 specific stuff goes here...

src/frontends/qt4/GuiApplication.h

@@ -175,7 +175,8 @@ public:
 	bool longOperationCancelled();
 	/// Stop the long operation mode (i.e., release the GUI)
 	void stopLongOperation();
-
+	/// A started long operation is still in progress ?
+	bool longOperationStarted();
 private Q_SLOTS:
 	///
 	void execBatchCommands();