add function to stop threads and make queue empty publicly accessible

include/actsim_agent/task_interface.hpp

@@ -53,12 +53,13 @@ class TaskInterface {
     bool fresh_buffer_full();
 
     bool running() { return !this->stop_flag.load(std::memory_order_relaxed); };
-
-    private:
+    void stop() { this->stop_flag.store(false, std::memory_order_relaxed); };
 
     bool fresh_queue_empty();
     bool finished_queue_empty();
 
+    private:
+
     size_t buffer_size;
 
     std::queue<std::unique_ptr<Task>> fresh_queue;