X11: Better timestamp handling for _NET_ACTIVE_WINDOW

ui/views/widget/desktop_aura/x11_desktop_handler.cc

 // Copyright (c) 2012 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.
 
 #include "ui/views/widget/desktop_aura/x11_desktop_handler.h"
 
 #include <X11/Xatom.h>
 #include <X11/Xlib.h>
 
 #include "base/message_loop/message_loop.h"
@@ skipping 25 matching lines @@
   if (!g_handler)
     g_handler = new X11DesktopHandler;
 
   return g_handler;
 }
 
 X11DesktopHandler::X11DesktopHandler()
     : xdisplay_(gfx::GetXDisplay()),
       x_root_window_(DefaultRootWindow(xdisplay_)),
       x_active_window_(None),
-      wm_user_time_ms_(0),
+      wm_user_time_ms_(CurrentTime),
       current_window_(None),
       current_window_active_state_(NOT_ACTIVE),
       atom_cache_(xdisplay_, kAtomsToCache),
       wm_supports_active_window_(false) {
   if (ui::PlatformEventSource::GetInstance())
     ui::PlatformEventSource::GetInstance()->AddPlatformEventDispatcher(this);
   aura::Env::GetInstance()->AddObserver(this);
 
   XWindowAttributes attr;
   XGetWindowAttributes(xdisplay_, x_root_window_, &attr);
@@ skipping 27 matching lines @@
     // Go through the regular activation path such that calling
     // DeactivateWindow() and ActivateWindow() immediately afterwards results
     // in an active X window.
   }
 
   if (wm_supports_active_window_) {
     DCHECK_EQ(gfx::GetXDisplay(), xdisplay_);
 
     // If the window is not already active, send a hint to activate it
     if (x_active_window_ != window) {
+      if (wm_user_time_ms_ == CurrentTime) {
+        set_wm_user_time_ms(
+            ui::X11EventSource::GetInstance()->UpdateServerTime());
+      }
       XEvent xclient;
       memset(&xclient, 0, sizeof(xclient));
       xclient.type = ClientMessage;
       xclient.xclient.window = window;
       xclient.xclient.message_type = atom_cache_.GetAtom("_NET_ACTIVE_WINDOW");
       xclient.xclient.format = 32;
       xclient.xclient.data.l[0] = 1;  // Specified we are an app.
       xclient.xclient.data.l[1] = wm_user_time_ms_;
       xclient.xclient.data.l[2] = None;
       xclient.xclient.data.l[3] = 0;
       xclient.xclient.data.l[4] = 0;
 
       XSendEvent(xdisplay_, x_root_window_, False,
                  SubstructureRedirectMask | SubstructureNotifyMask,
                  &xclient);
     } else {
       OnActiveWindowChanged(window, ACTIVE);
     }
   } else {
     XRaiseWindow(xdisplay_, window);
     // Directly ask the X server to give focus to the window. Note
     // that the call will raise an X error if the window is not
     // mapped.
     XSetInputFocus(xdisplay_, window, RevertToParent, CurrentTime);
 
     OnActiveWindowChanged(window, ACTIVE);
   }
 }
 
+void X11DesktopHandler::set_wm_user_time_ms(Time time_ms) {
+  if (time_ms != CurrentTime) {
+    int64_t event_time_64 = time_ms;
+    int64_t time_difference = wm_user_time_ms_ - event_time_64;
+    // Ignore timestamps that go backwards. However, X server time is a 32-bit
+    // millisecond counter, so if the time goes backwards by more than half the
+    // range of the 32-bit counter, treat it as a rollover.
+    if (time_difference < 0 || time_difference > (UINT32_MAX >> 1))
+      wm_user_time_ms_ = time_ms;
+  }
+}
+
 void X11DesktopHandler::DeactivateWindow(::Window window) {
   if (!IsActiveWindow(window))
     return;
 
   XLowerWindow(xdisplay_, window);
 
   // Per ICCCM: http://tronche.com/gui/x/icccm/sec-4.html#s-4.1.7
   // "Clients should not give up the input focus of their own volition.
   // They should ignore input that they receive instead."
   //
@@ skipping 118 matching lines @@
     ui::XMenuList::GetInstance()->MaybeUnregisterMenu(window);
   }
 
   if (event_type == DestroyNotify) {
     // Notify the XForeignWindowManager that |window| has been destroyed.
     ui::XForeignWindowManager::GetInstance()->OnWindowDestroyed(window);
   }
 }
 
 }  // namespace views