linux: fix single-instance logic (#314)

Replaced the previous QSharedMemory-based single-instance logic with a
clean QLocalServer approach. The old method left stale shared memory and
socket files after crashes, causing false "already running" states and
occasional segmentation faults.

Author: ozan956

linux/main.cpp

@@ -987,30 +987,24 @@ private slots:
 int main(int argc, char *argv[]) {
     QApplication app(argc, argv);
 
-    QSharedMemory sharedMemory;
-    sharedMemory.setKey("TcpServer-Key2");
+    QLocalServer::removeServer("app_server");
 
-    // Check if app is already open
-    if(sharedMemory.create(1) == false)
-    {
-        LOG_INFO("Another instance already running! Opening App Window Instead");
-        QLocalSocket socket;
-        // Connect to the original app, then trigger the reopen signal
-        socket.connectToServer("app_server");
-        if (socket.waitForConnected(500)) {
-            socket.write("reopen");
-            socket.flush();
-            socket.waitForBytesWritten(500);
-            socket.disconnectFromServer();
-            app.exit(); // exit; process already running
-            return 0;
-        }
-        else
-        {
-            // Failed connection, log and open the app (assume it's not running)
-            LOG_ERROR("Failed to connect to the original app instance. Assuming it is not running.");
-            LOG_DEBUG("Socket error: " << socket.errorString());
-        }
+    QFile stale("/tmp/app_server");
+    if (stale.exists())
+        stale.remove();
+
+    QLocalSocket socket_check;
+    socket_check.connectToServer("app_server");
+
+    if (socket_check.waitForConnected(300)) {
+        LOG_INFO("Another instance already running! Reopening window...");
+
+        socket_check.write("reopen");
+        socket_check.flush();
+        socket_check.waitForBytesWritten(200);
+        socket_check.disconnectFromServer();
+
+        return 0;
     }
     app.setDesktopFileName("me.kavishdevar.librepods");
     app.setQuitOnLastWindowClosed(false);
@@ -1092,8 +1086,16 @@ int main(int argc, char *argv[]) {
     });
 
     QObject::connect(&app, &QCoreApplication::aboutToQuit, [&]() {
-        LOG_DEBUG("Application is about to quit. Cleaning up...");
-        sharedMemory.detach();
+        LOG_DEBUG("Application quitting. Cleaning up local server...");
+
+        if (server.isListening()) {
+            server.close();
+        }
+
+        QLocalServer::removeServer("app_server");
+        QFile stale("/tmp/app_server");
+        if (stale.exists())
+            stale.remove();
     });
     return app.exec();
 }