Replace wait_for_response with handle callback

The poll-loop could in theory swallow events which would not be seen by
the main eventloop

include/components/screen.hpp

@@ -16,7 +16,7 @@ class logger;
 class connection;
 class signal_emitter;
 
-class screen : public xpp::event::sink<evt::randr_screen_change_notify> {
+class screen : public xpp::event::sink<evt::map_notify, evt::randr_screen_change_notify> {
  public:
   using make_type = unique_ptr<screen>;
   static make_type make();
@@ -25,6 +25,7 @@ class screen : public xpp::event::sink<evt::randr_screen_change_notify> {
   ~screen();
 
  protected:
+  void handle(const evt::map_notify& evt) override;
   void handle(const evt::randr_screen_change_notify& evt) override;
 
  private:
@@ -42,6 +43,12 @@ class screen : public xpp::event::sink<evt::randr_screen_change_notify> {
   };
   bool m_sigraised{false};
 
+  /**
+   * Original event mask on the root window.
+   * Used to restore event mask after the proxy window is mapped.
+   */
+  uint32_t m_root_mask{0};
+
   bool have_monitors_changed() const;
 };
 

include/x11/connection.hpp

@@ -129,27 +129,6 @@ class connection : public detail::connection_base<connection&, XPP_EXTENSION_LIS
 
   void dispatch_event(const shared_ptr<xcb_generic_event_t>& evt) const;
 
-  template <typename Event, unsigned int ResponseType>
-  void wait_for_response(function<bool(const Event*)> check_event) {
-    int fd = get_file_descriptor();
-    shared_ptr<xcb_generic_event_t> evt{};
-    while (!connection_has_error()) {
-      fd_set fds;
-      FD_ZERO(&fds);
-      FD_SET(fd, &fds);
-
-      if (!select(fd + 1, &fds, nullptr, nullptr, nullptr)) {
-        continue;
-      } else if ((evt = shared_ptr<xcb_generic_event_t>(xcb_poll_for_event(*this), free)) == nullptr) {
-        continue;
-      } else if (evt->response_type != ResponseType) {
-        continue;
-      } else if (check_event(reinterpret_cast<const Event*>(&*evt))) {
-        break;
-      }
-    }
-  }
-
   template <typename Sink>
   void attach_sink(Sink&& sink, registry::priority prio = 0) {
     m_registry.attach(prio, forward<Sink>(sink));

src/components/screen.cpp

@@ -54,27 +54,19 @@ screen::screen(connection& conn, signal_emitter& emitter, const logger& logger,
 
   // Update the root windows event mask
   auto attributes = m_connection.get_window_attributes(m_root);
-  auto root_mask = attributes->your_event_mask;
+  m_root_mask = attributes->your_event_mask;
   attributes->your_event_mask = attributes->your_event_mask | XCB_EVENT_MASK_SUBSTRUCTURE_NOTIFY;
   m_connection.change_window_attributes(m_root, XCB_CW_EVENT_MASK, &attributes->your_event_mask);
 
   // Receive randr events
   m_connection.randr().select_input(m_proxy, XCB_RANDR_NOTIFY_MASK_SCREEN_CHANGE);
 
+  // Attach the sink to process randr events
+  m_connection.attach_sink(this, SINK_PRIORITY_SCREEN);
+
   // Create window used as event proxy
   m_connection.map_window(m_proxy);
   m_connection.flush();
-
-  // Wait until the proxy window has been mapped
-  // TODO replace wait with a `handle` method
-  using evt = xcb_map_notify_event_t;
-  m_connection.wait_for_response<evt, XCB_MAP_NOTIFY>([&](const evt* evt) -> bool { return evt->window == m_proxy; });
-
-  // Restore the root windows event mask
-  m_connection.change_window_attributes(m_root, XCB_CW_EVENT_MASK, &root_mask);
-
-  // Finally attach the sink the process randr events
-  m_connection.attach_sink(this, SINK_PRIORITY_SCREEN);
 }
 
 /**
@@ -88,6 +80,15 @@ screen::~screen() {
   }
 }
 
+void screen::handle(const evt::map_notify& evt) {
+  if (evt->window != m_proxy) {
+    return;
+  }
+
+  // Once the proxy window has been mapped, restore the original root window event mask.
+  m_connection.change_window_attributes(m_root, XCB_CW_EVENT_MASK, &m_root_mask);
+}
+
 /**
  * Handle XCB_RANDR_SCREEN_CHANGE_NOTIFY events
  *