Reset accessibility if it gets out of sync.

content/browser/frame_host/render_frame_host_impl.cc

 // Copyright 2013 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 "content/browser/frame_host/render_frame_host_impl.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/containers/hash_tables.h"
 #include "base/lazy_instance.h"
@@ skipping 50 matching lines @@
 #if defined(OS_MACOSX)
 #include "content/browser/frame_host/popup_menu_helper_mac.h"
 #endif
 
 using base::TimeDelta;
 
 namespace content {
 
 namespace {
 
+// An accessibility reset is only allowed to prevent very rare corner cases
+// or race conditions where the browser and renderer get out of sync. If
+// this happens more than this many times, kill the renderer.
+const int kMaxAccessibilityResets = 5;
+
 // The (process id, routing id) pair that identifies one RenderFrame.
 typedef std::pair<int32, int32> RenderFrameHostID;
 typedef base::hash_map<RenderFrameHostID, RenderFrameHostImpl*>
     RoutingIDFrameMap;
 base::LazyInstance<RoutingIDFrameMap> g_routing_id_frame_map =
     LAZY_INSTANCE_INITIALIZER;
 
 class DesktopNotificationDelegateImpl : public DesktopNotificationDelegate {
  public:
   DesktopNotificationDelegateImpl(RenderFrameHost* render_frame_host,
@@ skipping 92 matching lines @@
     : render_view_host_(render_view_host),
       delegate_(delegate),
       cross_process_frame_connector_(NULL),
       render_frame_proxy_host_(NULL),
       frame_tree_(frame_tree),
       frame_tree_node_(frame_tree_node),
       routing_id_(routing_id),
       is_swapped_out_(is_swapped_out),
       render_frame_created_(false),
       navigations_suspended_(false),
+      waiting_on_accessibility_reset_(false),
+      accessibility_reset_count_(0),
+      disallow_browser_accessibility_manager_for_testing_(false),
       weak_ptr_factory_(this) {
   frame_tree_->RegisterRenderFrameHost(this);
   GetProcess()->AddRoute(routing_id_, this);
   g_routing_id_frame_map.Get().insert(std::make_pair(
       RenderFrameHostID(GetProcess()->GetID(), routing_id_),
       this));
 
   if (GetProcess()->GetServiceRegistry()) {
     RenderFrameSetupPtr setup;
     GetProcess()->GetServiceRegistry()->ConnectToRemoteService(&setup);
@@ skipping 253 matching lines @@
   if (view)
     return view->AccessibilityOriginInScreen(bounds);
   return gfx::Point();
 }
 
 void RenderFrameHostImpl::AccessibilityHitTest(const gfx::Point& point) {
   Send(new AccessibilityMsg_HitTest(routing_id_, point));
 }
 
 void RenderFrameHostImpl::AccessibilityFatalError() {
-  Send(new AccessibilityMsg_FatalError(routing_id_));
   browser_accessibility_manager_.reset(NULL);
+  if (waiting_on_accessibility_reset_)
+    return;
+
+  accessibility_reset_count_++;

[nasko, 2014/10/02 16:38:48]

This is never reset to 0, even when the renderer is killed. The user can reload
a tab with killed renderer, but RFH will not be recreated for the top-level
frame, so this will just keep on killing the renderer.

[dmazzoni, 2014/10/02 21:51:12]

Good point. I reset it in OnDidStartProvisionalLoadForFrame, in manual testing
that seemed to work if I reload a page but not otherwise. Does that look good or
can you think of a better place?

+  if (accessibility_reset_count_ >= kMaxAccessibilityResets) {
+    Send(new AccessibilityMsg_FatalError(routing_id_));
+  } else {
+    Send(new AccessibilityMsg_Reset(routing_id_));

[nasko, 2014/10/02 16:38:48]

Do you want to UMA stat how often this happens? According to the comments, it
should be very rare, so some concrete confirmation through data might be useful.

[dmazzoni, 2014/10/02 21:51:12]

Great idea. I added three counts that should be enough to give us a good sense
of how often this is happening.

+    waiting_on_accessibility_reset_ = true;
+  }
 }
 
 gfx::AcceleratedWidget
     RenderFrameHostImpl::AccessibilityGetAcceleratedWidget() {
   RenderWidgetHostViewBase* view = static_cast<RenderWidgetHostViewBase*>(
       render_view_host_->GetView());
   if (view)
     return view->AccessibilityGetAcceleratedWidget();
   return gfx::kNullAcceleratedWidget;
 }
@@ skipping 553 matching lines @@
 }
 
 void RenderFrameHostImpl::OnBeginNavigation(
     const FrameHostMsg_BeginNavigation_Params& params) {
   CHECK(CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kEnableBrowserSideNavigation));
   frame_tree_node()->render_manager()->OnBeginNavigation(params);
 }
 
 void RenderFrameHostImpl::OnAccessibilityEvents(
-    const std::vector<AccessibilityHostMsg_EventParams>& params) {
+    const std::vector<AccessibilityHostMsg_EventParams>& params,
+    bool is_reset) {
+  // Don't process this IPC if either we're waiting on a reset and this
+  // isn't a reset, or if we're not waiting on a reset but this is a reset.
+  if (waiting_on_accessibility_reset_ != is_reset) {
+    Send(new AccessibilityMsg_Events_ACK(routing_id_));
+    return;
+  }
+  waiting_on_accessibility_reset_ = false;
+
   RenderWidgetHostViewBase* view = static_cast<RenderWidgetHostViewBase*>(
       render_view_host_->GetView());
 
   AccessibilityMode accessibility_mode = delegate_->GetAccessibilityMode();
   if ((accessibility_mode != AccessibilityModeOff) && view &&
       RenderViewHostImpl::IsRVHStateActive(render_view_host_->rvh_state())) {
     if (accessibility_mode & AccessibilityModeFlagPlatform) {
       GetOrCreateBrowserAccessibilityManager();
       if (browser_accessibility_manager_)
         browser_accessibility_manager_->OnAccessibilityEvents(params);
@@ skipping 54 matching lines @@
     } else {
       CHECK(ax_tree_for_testing_->Unserialize(param.update))
           << ax_tree_for_testing_->error();
     }
     accessibility_testing_callback_.Run(param.event_type, param.id);
   }
 }
 
 void RenderFrameHostImpl::OnAccessibilityLocationChanges(
     const std::vector<AccessibilityHostMsg_LocationChangeParams>& params) {
+  if (waiting_on_accessibility_reset_)
+    return;
+
   RenderWidgetHostViewBase* view = static_cast<RenderWidgetHostViewBase*>(
       render_view_host_->GetView());
   if (view &&
       RenderViewHostImpl::IsRVHStateActive(render_view_host_->rvh_state())) {
     AccessibilityMode accessibility_mode = delegate_->GetAccessibilityMode();
     if (accessibility_mode & AccessibilityModeFlagPlatform) {
       if (!browser_accessibility_manager_) {
         browser_accessibility_manager_.reset(
             view->CreateBrowserAccessibilityManager(this));
       }
@@ skipping 249 matching lines @@
     const base::Callback<void(ui::AXEvent, int)>& callback) {
   accessibility_testing_callback_ = callback;
 }
 
 const ui::AXTree* RenderFrameHostImpl::GetAXTreeForTesting() {
   return ax_tree_for_testing_.get();
 }
 
 BrowserAccessibilityManager*
     RenderFrameHostImpl::GetOrCreateBrowserAccessibilityManager() {
+  if (disallow_browser_accessibility_manager_for_testing_)
+    return NULL;
+
   RenderWidgetHostViewBase* view = static_cast<RenderWidgetHostViewBase*>(
       render_view_host_->GetView());
   if (view &&
       !browser_accessibility_manager_) {
     browser_accessibility_manager_.reset(
         view->CreateBrowserAccessibilityManager(this));
   }
   return browser_accessibility_manager_.get();
 }
 
@@ skipping 79 matching lines @@
   // Clear any state if a pending navigation is canceled or preempted.
   if (suspended_nav_params_)
     suspended_nav_params_.reset();
 
   TRACE_EVENT_ASYNC_END0("navigation",
                          "RenderFrameHostImpl navigation suspended", this);
   navigations_suspended_ = false;
 }
 
 }  // namespace content