Added cpp style mechanisme to queue callables on window thread.

mainwindow.cpp

@@ -5,6 +5,7 @@
 #include "QueryExplainModel.h"
 #include "sqlhighlighter.h"
 #include <QTextTable>
+#include <QTimer>
 #include <windows.h>
 #include "json/json.h"
 #include "explaintreemodelitem.h"
@@ -59,6 +60,34 @@ MainWindow::MainWindow(QWidget *parent) :
 MainWindow::~MainWindow()
 {}
 
+void MainWindow::QueueTask(callable c)
+{
+	std::lock_guard<std::mutex> lg(m_mutexCallableQueue);
+	m_callableQueue.emplace_back(std::move(c));
+	// Theoretically this needs to be only called if the queue was empty because otherwise it already would
+	// be busy emptying the queue. For now however I think it is safer to call it just to make sure.
+	QMetaObject::invokeMethod(this, "processCallableQueue",	Qt::QueuedConnection); // queues on main thread
+}
+
+void MainWindow::processCallableQueue()
+{
+	bool empty;
+	callable c;
+	{ // narrow scope for lock guard
+		std::lock_guard<std::mutex> lg(m_mutexCallableQueue);
+		c = m_callableQueue.back();
+		m_callableQueue.pop_back();
+		empty = m_callableQueue.empty();
+	}
+
+	c();
+
+	if (!empty) {
+		// This gives other events a chance to be processed to keep the UI snappy.
+		QTimer::singleShot(0, this, SLOT(processCallableQueue()));
+	}
+}
+
 void MainWindow::startConnect()
 {
 	if (connection == nullptr) {
@@ -125,6 +154,7 @@ void MainWindow::performQuery()
 			QMetaObject::invokeMethod(this, "query_ready",	 Qt::QueuedConnection); // queues on main thread
 			return res;
 		});
+
 }
 
 void MainWindow::query_ready()

mainwindow.h

@@ -22,15 +22,36 @@ namespace Pgsql {
 
 }
 
+#include <deque>
+#include <mutex>
+
+class TaskQueue {
+public:
+
+private:
+};
+
 class MainWindow : public QMainWindow
 {
 	Q_OBJECT
 
 public:
+	using callable = std::function<void()>;
+
 	explicit MainWindow(QWidget *parent = 0);
 	~MainWindow();
 
+	/* Meant to be called from other threads to pass a code block
+	 * that has to be executed in the context of the thread of the window.
+	 */
+	void QueueTask(callable c);
+
 private:
+	using t_CallableQueue = std::deque<callable>;
+	std::mutex m_mutexCallableQueue;
+	t_CallableQueue m_callableQueue;
+
+
 	std::unique_ptr<Ui::MainWindow> ui;
 	std::unique_ptr<SqlHighlighter> highlighter;
 
@@ -65,7 +86,7 @@ private slots:
 	void cancel_query();
 	void receiveNotice(Pgsql::ErrorDetails notice);
 
-
+	void processCallableQueue();
 };
 
 #endif // MAINWINDOW_H