Avoid heavy weight function object

Also, by switching to template we can avoid the cost of converting to some specific type and
perfectly forward the parameter to the final function.

PR #21572.

src/base/bittorrent/sessionimpl.h

@@ -44,6 +44,7 @@
 #include <QMap>
 #include <QPointer>
 #include <QSet>
+#include <QThreadPool>
 
 #include "base/path.h"
 #include "base/settingvalue.h"
@@ -57,7 +58,6 @@
 #include "trackerentrystatus.h"
 
 class QString;
-class QThreadPool;
 class QTimer;
 class QUrl;
 
@@ -482,7 +482,11 @@ namespace BitTorrent
             QMetaObject::invokeMethod(this, std::forward<Func>(func), Qt::QueuedConnection);
         }
 
-        void invokeAsync(std::function<void ()> func);
+        template <typename Func>
+        void invokeAsync(Func &&func)
+        {
+            m_asyncWorker->start(std::forward<Func>(func));
+        }
 
     signals:
         void addTorrentAlertsReceived(qsizetype count);