Use separate thread for saving session data.

src/globals.h

@@ -1,14 +1,38 @@
 #ifndef TORRENT_GLOBALS_H
 #define TORRENT_GLOBALS_H
 
-#include "thread_worker.h"
+#include <torrent/common.h>
+
 #include "rpc/ip_table_list.h"
 
 class Control;
+class ThreadWorker;
 
-extern rpc::ip_table_list          ip_tables;
+extern rpc::ip_table_list ip_tables;
 
 extern Control*      control;
+
+// TODO: Update to new thread model.
 extern ThreadWorker* worker_thread;
 
+namespace session {
+
+class SessionManager;
+
+} // namespace session
+
+
+namespace session_thread {
+
+torrent::utils::Thread* thread();
+std::thread::id         thread_id();
+
+void                    callback(void* target, std::function<void ()>&& fn);
+void                    cancel_callback(void* target);
+void                    cancel_callback_and_wait(void* target);
+
+session::SessionManager* manager();
+
+} // namespace torrent::session_thread
+
 #endif