Destroy the QMdnsEngine Server and Cache when not polling

These set background timers to refresh state, rebind sockets,
and refresh the cache. This is all stuff that we don't want to
be doing while streaming.

app/backend/computermanager.h

@@ -42,11 +42,11 @@ class MdnsPendingComputer : public QObject
     Q_OBJECT
 
 public:
-    explicit MdnsPendingComputer(QMdnsEngine::Server* server,
+    explicit MdnsPendingComputer(const QSharedPointer<QMdnsEngine::Server> server,
                                  const QMdnsEngine::Service& service)
         : m_Hostname(service.hostname()),
           m_Port(service.port()),
-          m_Server(server),
+          m_ServerWeak(server),
           m_Resolver(nullptr)
     {
         // Start resolving
@@ -94,8 +94,21 @@ signals:
 private:
     void resolve()
     {
+        // Delete our resolver, so we're guaranteed that nothing is referencing m_Server.
         delete m_Resolver;
-        m_Resolver = new QMdnsEngine::Resolver(m_Server, m_Hostname);
+        m_Resolver = nullptr;
+
+        // Now delete our strong reference that we held on behalf of m_Resolver.
+        // The server may be destroyed after we make this call.
+        m_Server.reset();
+
+        // Re-acquire a strong reference if the server still exists.
+        m_Server = m_ServerWeak.toStrongRef();
+        if (!m_Server) {
+            return;
+        }
+
+        m_Resolver = new QMdnsEngine::Resolver(m_Server.get(), m_Hostname);
         connect(m_Resolver, &QMdnsEngine::Resolver::resolved,
                 this, &MdnsPendingComputer::handleResolvedAddress);
         QTimer::singleShot(2000, this, &MdnsPendingComputer::handleResolvedTimeout);
@@ -103,7 +116,8 @@ private:
 
     QByteArray m_Hostname;
     uint16_t m_Port;
-    QMdnsEngine::Server* m_Server;
+    QWeakPointer<QMdnsEngine::Server> m_ServerWeak;
+    QSharedPointer<QMdnsEngine::Server> m_Server;
     QMdnsEngine::Resolver* m_Resolver;
     QVector<QHostAddress> m_Addresses;
 };
@@ -245,9 +259,8 @@ private:
     QReadWriteLock m_Lock;
     QMap<QString, NvComputer*> m_KnownHosts;
     QMap<QString, ComputerPollingEntry*> m_PollEntries;
-    QMdnsEngine::Server m_MdnsServer;
+    QSharedPointer<QMdnsEngine::Server> m_MdnsServer;
     QMdnsEngine::Browser* m_MdnsBrowser;
-    QMdnsEngine::Cache m_MdnsCache;
     QVector<MdnsPendingComputer*> m_PendingResolution;
     CompatFetcher m_CompatFetcher;
     DelayedFlushThread* m_DelayedFlushThread;