Add notification on second simultaneous launch

src/third-party/singleapplication/singleapplication.cpp

@@ -32,6 +32,8 @@
 #include <QtCore/QDataStream>
 #include <QtNetwork/QLocalServer>
 #include <QtNetwork/QLocalSocket>
+#include <QMessageBox>
+#include <QTimer>
 
 #ifdef Q_OS_UNIX
     #include <signal.h>
@@ -415,6 +417,26 @@ SingleApplication::SingleApplication( int &argc, char *argv[], bool allowSeconda
 
     d->connectToPrimary( timeout, SingleApplicationPrivate::NewInstance );
     delete d;
+
+    // show message box with inforation that Flameshot is already launched
+    QMessageBox msgBox;
+    msgBox.setText(QObject::tr("Hi, I'm already running!\nYou can find me in the system tray."));
+    int cnt = 3;
+    QTimer cntDown;
+    QObject::connect(
+                &cntDown,
+                &QTimer::timeout,
+                [&msgBox,&cnt, &cntDown]()->void{
+                    if(--cnt < 0){
+                         cntDown.stop();
+                         msgBox.close();
+                     } else {
+                        msgBox.setWindowTitle(QString("Flameshot (%1)").arg(cnt + 1));
+                     }
+                 });
+    cntDown.start(1000);
+    msgBox.exec();
+
     ::exit( EXIT_SUCCESS );
 }