X11: Add window cache

ui/base/x/x11_window_cache.h

Index: ui/base/x/x11_window_cache.h
diff --git a/ui/base/x/x11_window_cache.h b/ui/base/x/x11_window_cache.h
new file mode 100644
index 0000000000000000000000000000000000000000..7148c0773c3039c0fae6c1875973b141f5ff9b55
--- /dev/null
+++ b/ui/base/x/x11_window_cache.h
@@ -0,0 +1,133 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_BASE_X_X11_WINDOW_CACHE_H_
+#define UI_BASE_X_X11_WINDOW_CACHE_H_
+
+#include <xcb/xcb.h>
+
+#include <list>
+#include <map>
+
+#include "ui/base/x/ui_base_x_export.h"
+#include "ui/events/platform/platform_event_observer.h"
+#include "ui/gfx/x/x11_types.h"
+
+namespace ui {
+
+class X11EventSource;
+
+// Keep tabs on the window tree starting from a root window.
+class UI_BASE_X_EXPORT XWindowCache : public PlatformEventObserver {
+ private:
+  struct GetWindowAttributesRequest;
+  struct GetGeometryRequest;
+  struct ListPropertiesRequest;
+  struct QueryTreeRequest;
+  struct GetPropertyRequest;
+
+ public:
+  // Clients should not modify any members of Property.
+  struct Window;
+  struct Property {
+    Property(xcb_atom_t name, Window* window, XWindowCache* cache);
+    ~Property();
+
+    xcb_atom_t name;
+
+    GetPropertyRequest* property_request;
+    xcb_atom_t type;
+    // Format can be 8, 16, or 32, indicating how |data| should be interpreted.
+    uint8_t data_format;
+    int data_length;
+    union {
+      uint8_t* bits_8;
+      uint16_t* bits_16;
+      uint32_t* bits_32;
+    } data;
+
+    XWindowCache* cache_;
+  };
+
+  // Clients should not modify any members of Window.
+  struct Window {
+    Window(xcb_window_t id, Window* parent, XWindowCache* cache);
+    ~Window();
+
+    xcb_window_t id;
+    Window* parent;
+
+    GetWindowAttributesRequest* attributes_request;

[Daniel Erat, 2016/09/06 20:35:58]

storing information about requests inside of the Window and Property classes
like this feels confusing to me -- ownership of these objects is unclear and
there's a lot of reaching up and down in the class hierarchy and modifying other
objects' members directly.

i'd suggest exploring an approach where the Property and Window structs only
hold the information that's needed by clients (id, parent, override_redirect,
geometry data, etc.) and all of the implementation lives inside of XWindowCache
or other private classes within it.

+    bool override_redirect;
+    // |is_mapped| is different from the map_state that is returned by
+    // XGetWindowAttributes.  map_state can be one of IsUnmapped, IsUnviewable,
+    // or IsViewable.  map_state is set to IsUnviewable when the window is
+    // mapped but some ancestor window is unmapped.  If you need to check for
+    // this case, you must do so manually.
+    bool is_mapped;
+
+    GetGeometryRequest* geometry_request;
+    int16_t x, y;
+    uint16_t width, height;
+    uint16_t border_width;
+
+    ListPropertiesRequest* properties_request;
+    std::map<xcb_atom_t, std::unique_ptr<Property>> properties;
+
+    QueryTreeRequest* children_request;
+    std::list<std::unique_ptr<Window>> children;
+
+    const Property* GetProperty(XID atom) const;

[Daniel Erat, 2016/09/06 20:35:58]

see the style guide's guidance on using structs vs. classes:
https://google.github.io/styleguide/cppguide.html#Structs_vs._Classes

there also shouldn't be private-esque members like |cache_| inside of a struct.

+
+    XWindowCache* cache_;
+  };
+
+  XWindowCache(XDisplay* display, X11EventSource* event_source, XID root);
+  ~XWindowCache() override;
+
+  // Returns null when window |id| is not cached.
+  const Window* GetWindow(XID id) const;

[Daniel Erat, 2016/09/06 20:35:58]

please document the lifetime of the returned object. can the caller hang onto it
at all, or is it possible it'll be deleted as soon as events are pulled off of
the X queue?

+
+ protected:
+  // Overridden from PlatformEventDispatcher:
+  void WillProcessEvent(const PlatformEvent& event) override;
+  void DidProcessEvent(const PlatformEvent& event) override;
+
+ private:
+  friend class XWindowCacheTest;
+
+  // Clears all state and rebuilds the entire cache.
+  void ResetCache();
+  void ResetCacheImpl();
+
+  // Creates and adds a new property to |window|.
+  void CacheProperty(Window* window, xcb_atom_t atom);
+
+  // Allocates/Deallocates a Window.  Responsible for setting up and breaking
+  // parent/child relationships.
+  void CreateWindow(xcb_window_t id, XWindowCache::Window* parent);
+  void DestroyWindow(Window* window);
+
+  void ProcessEvent(const XEvent* event);
+
+  Window* GetWindowInternal(XID id) const;
+
+  XDisplay* display_;
+  xcb_connection_t* connection_;
+  xcb_window_t root_id_;
+
+  X11EventSource* event_source_;
+
+  std::unique_ptr<Window> root_;
+  std::map<xcb_window_t, Window*> windows_;
+
+  // Don't cache icon properties because they take up too much space and we
+  // currently never use them.
+  xcb_intern_atom_cookie_t net_wm_icon_cookie_;
+  xcb_atom_t net_wm_icon_;

[Daniel Erat, 2016/09/06 20:35:58]

put DISALLOW_COPY_AND_ASSIGN at the end of classes like this one that shouldn't
be copied

+};
+
+}  // namespace ui
+
+#endif  // UI_BASE_X_X11_WINDOW_CACHE_H_