Allow only one application instance

fixes #141

include/RunGuard.h

@@ -0,0 +1,31 @@
+#pragma once
+
+//
+// Taken from
+// https://stackoverflow.com/questions/5006547/qt-best-practice-for-a-single-instance-app-protection
+//
+
+#include <QObject>
+#include <QSharedMemory>
+#include <QSystemSemaphore>
+
+class RunGuard
+{
+public:
+        RunGuard(const QString &key);
+        ~RunGuard();
+
+        bool isAnotherRunning();
+        bool tryToRun();
+        void release();
+
+private:
+        const QString key;
+        const QString memLockKey;
+        const QString sharedmemKey;
+
+        QSharedMemory sharedMem;
+        QSystemSemaphore memLock;
+
+        Q_DISABLE_COPY(RunGuard)
+};