response to the shutdown

include/GLFW/glfw3.h

@@ -1422,10 +1422,11 @@ typedef void (* GLFWwindowclosefun)(GLFWwindow*);
  *
  *  @sa @ref machine_shutdown
  *  @sa @ref glfwSetMachineShutdownCallback
+ *  @return GLFW_TRUE to accept the shutdown or GLFW_FALSE to interrupt it
  *
  *  @ingroup window
  */
-typedef void (* GLFWmachineShutdownfun)(GLFWwindow*);
+typedef int (* GLFWmachineShutdownfun)(GLFWwindow*);
 
 /*! @brief The function pointer type for window content refresh callbacks.
  *

src/internal.h

@@ -730,7 +730,7 @@ void _glfwInputWindowIconify(_GLFWwindow* window, GLFWbool iconified);
 void _glfwInputWindowMaximize(_GLFWwindow* window, GLFWbool maximized);
 void _glfwInputWindowDamage(_GLFWwindow* window);
 void _glfwInputWindowCloseRequest(_GLFWwindow* window);
-void _glfwInputMachineShutdown(_GLFWwindow* window);
+GLFWbool _glfwInputMachineShutdown(_GLFWwindow* window);
 void _glfwInputWindowMonitor(_GLFWwindow* window, _GLFWmonitor* monitor);
 
 void _glfwInputKey(_GLFWwindow* window,

src/win32_window.c

@@ -627,6 +627,11 @@ static LRESULT CALLBACK windowProc(HWND hWnd, UINT uMsg,
             return 0;
         }
 
+        case WM_QUERYENDSESSION:
+        {
+            return _glfwInputMachineShutdown(window);
+        }
+
         case WM_INPUTLANGCHANGE:
         {
             _glfwUpdateKeyNamesWin32();
@@ -1199,13 +1204,6 @@ static LRESULT CALLBACK windowProc(HWND hWnd, UINT uMsg,
             DragFinish(drop);
             return 0;
         }
-
-        case WM_QUERYENDSESSION:
-        case WM_ENDSESSION:
-        {
-            _glfwInputMachineShutdown(window);
-            return 0;
-        }
     }
 
     return DefWindowProcW(hWnd, uMsg, wParam, lParam);

src/window.c

@@ -140,10 +140,12 @@ void _glfwInputWindowCloseRequest(_GLFWwindow* window)
 
 // Notifies shared code that the machine is shuting down
 //
-void _glfwInputMachineShutdown(_GLFWwindow *window)
+GLFWbool _glfwInputMachineShutdown(_GLFWwindow *window)
 {
-    if (window->callbacks.shutdown)
+    if (window->callbacks.shutdown) {
-        window->callbacks.shutdown((GLFWwindow*) window);
+        return window->callbacks.shutdown((GLFWwindow*) window);
+    }
+    return GLFW_TRUE;
 }
 
 // Notifies shared code that a window has changed its desired monitor

tests/events.c

@@ -329,11 +329,12 @@ static void window_close_callback(GLFWwindow* window)
     glfwSetWindowShouldClose(window, slot->closeable);
 }
 
-static void window_machine_shutdown_callback(GLFWwindow* window)
+static int window_machine_shutdown_callback(GLFWwindow* window)
 {
     printf("%08x at %0.3f: Machine shutdown detected\n",
            counter++,
            glfwGetTime());
+    return GLFW_TRUE;
 }
 
 static void window_refresh_callback(GLFWwindow* window)