Use separate thread for saving session data.

src/session/thread_session.h

@@ -0,0 +1,43 @@
+#ifndef RTORRENT_SESSION_THREAD_SESSION_H
+#define RTORRENT_SESSION_THREAD_SESSION_H
+
+#include <torrent/utils/thread.h>
+
+namespace session {
+
+class SessionManager;
+class ThreadSessionInternal;
+
+class ThreadSession : public torrent::utils::Thread {
+public:
+
+  static void           create_thread();
+  static void           destroy_thread();
+  static ThreadSession* thread_session();
+
+  const char*         name() const override      { return "rtorrent-session"; }
+
+  void                init_thread() override;
+  void                cleanup_thread() override;
+
+  SessionManager*     manager() const { return m_manager.get(); }
+
+protected:
+  friend class ThreadSessionInternal;
+
+  ThreadSession() = default;
+
+  static auto         internal_thread_session() { return m_thread_session; }
+
+  void                      call_events() override;
+  std::chrono::microseconds next_timeout() override;
+
+private:
+  static ThreadSession*   m_thread_session;
+
+  std::unique_ptr<SessionManager> m_manager;
+};
+
+} // namespace session
+
+#endif // RTORRENT_SESSION_THREAD_SESSION_H