Randomize the listening port only on startup.

src/core/preferences.cpp

@@ -56,7 +56,7 @@
 
 Preferences* Preferences::m_instance = 0;
 
-Preferences::Preferences() : dirty(false), lock(QReadWriteLock::Recursive) {
+Preferences::Preferences() : m_randomPort(rand() % 64512 + 1024), dirty(false), lock(QReadWriteLock::Recursive) {
   QIniSettings *settings = new QIniSettings;
 #ifndef Q_OS_MAC
   QIniSettings *settings_new = new QIniSettings("qBittorrent", "qBittorrent_new");
@@ -537,6 +537,9 @@ void Preferences::setActionOnDblClOnTorrentFn(int act) {
 
 // Connection options
 int Preferences::getSessionPort() const {
+  QReadLocker locker(&lock);
+  if (useRandomPort())
+    return m_randomPort;
   return value("Preferences/Connection/PortRangeMin", 6881).toInt();
 }
 

src/core/preferences.h

@@ -63,6 +63,7 @@ private:
   explicit Preferences();
   static Preferences* m_instance;
   QHash<QString, QVariant> m_data;
+  int m_randomPort;
   bool dirty;
   QTimer timer;
   mutable QReadWriteLock lock;

src/core/qtlibtorrent/qbtsession.cpp

@@ -309,9 +309,6 @@ void QBtSession::setQueueingEnabled(bool enable) {
 void QBtSession::configureSession() {
   qDebug("Configuring session");
   Preferences* const pref = Preferences::instance();
-  if (pref->useRandomPort()) {
-    pref->setSessionPort(rand() % USHRT_MAX + 1025);
-  }
 
   const unsigned short old_listenPort = getListenPort();
   const unsigned short new_listenPort = pref->getSessionPort();