Fix periodic latency spikes on Windows with WiFi connections. Closes #4209.

src/app/main.cpp

@@ -215,6 +215,21 @@ int main(int argc, char *argv[])
         return EXIT_SUCCESS;
     }
 
+#if defined(Q_OS_WIN) && defined(QBT_USES_QT5)
+    // This affects only Windows apparently and Qt5.
+    // When QNetworkAccessManager is instantiated it regularly starts polling
+    // the network interfaces to see what's available and their status.
+    // This polling creates jitter and high ping with wifi interfaces.
+    // So here we disable it for lack of better measure.
+    // It will also spew this message in the console: QObject::startTimer: Timers cannot have negative intervals
+    // For more info see:
+    // 1. https://github.com/qbittorrent/qBittorrent/issues/4209
+    // 2. https://bugreports.qt.io/browse/QTBUG-40332
+    // 3. https://bugreports.qt.io/browse/QTBUG-46015
+
+    qputenv("QT_BEARER_POLL_TIMEOUT", QByteArray::number(-1));
+#endif
+
 #ifndef DISABLE_GUI
     if (!upgrade()) return EXIT_FAILURE;
 #else