add original source

source/listing_4.9.cpp

@@ -0,0 +1,40 @@
+#include <deque>
+#include <mutex>
+#include <future>
+#include <thread>
+#include <utility>
+
+std::mutex m;
+std::deque<std::packaged_task<void()> > tasks;
+
+bool gui_shutdown_message_received();
+void get_and_process_gui_message();
+
+void gui_thread()
+{
+    while(!gui_shutdown_message_received())
+    {
+        get_and_process_gui_message();
+        std::packaged_task<void()> task;
+        {
+            std::lock_guard<std::mutex> lk(m);
+            if(tasks.empty())
+                continue;
+            task=std::move(tasks.front());
+            tasks.pop_front();
+        }
+        task();
+    }
+}
+
+std::thread gui_bg_thread(gui_thread);
+
+template<typename Func>
+std::future<void> post_task_for_gui_thread(Func f)
+{
+    std::packaged_task<void()> task(f);
+    std::future<void> res=task.get_future();
+    std::lock_guard<std::mutex> lk(m);
+    tasks.push_back(std::move(task));
+    return res;
+}