Make tree id sequence in LayerTreeHost thread-safe.

cc/trees/layer_tree_host.cc

 // Copyright 2011 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 "cc/trees/layer_tree_host.h"
 
 #include <algorithm>
 #include <stack>
 #include <string>
 
+#include "base/atomic_sequence_num.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
+#include "base/lazy_instance.h"
 #include "base/message_loop/message_loop.h"
 #include "base/metrics/histogram.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "cc/animation/animation_registrar.h"
 #include "cc/animation/layer_animation_controller.h"
 #include "cc/base/math_util.h"
 #include "cc/debug/devtools_instrumentation.h"
 #include "cc/debug/overdraw_metrics.h"
 #include "cc/debug/rendering_stats_instrumentation.h"
@@ skipping 10 matching lines @@
 #include "cc/trees/layer_tree_host_common.h"
 #include "cc/trees/layer_tree_host_impl.h"
 #include "cc/trees/layer_tree_impl.h"
 #include "cc/trees/occlusion_tracker.h"
 #include "cc/trees/single_thread_proxy.h"
 #include "cc/trees/thread_proxy.h"
 #include "cc/trees/tree_synchronizer.h"
 #include "ui/gfx/size_conversions.h"
 
 namespace {
-static int s_num_layer_tree_instances;
+base::LazyInstance<base::AtomicSequenceNumber>
+    s_next_tree_id = LAZY_INSTANCE_INITIALIZER;
+
+inline int GetNextTreeId() {
+  static int initializeTo1 = s_next_tree_id.Pointer()->GetNext();
+  (void)initializeTo1;

[jamesr, 2013/11/04 19:18:01]

what does this line do? I don't think this complexity is necessary. this is
rarely called, can you just use an integer and a lock?

[dshwang, 2013/11/04 19:34:47]

Thank you for review. Done.

+  return s_next_tree_id.Pointer()->GetNext();
+}
 }
 
 namespace cc {
 
 RendererCapabilities::RendererCapabilities()
     : best_texture_format(RGBA_8888),
       using_partial_swap(false),
       using_set_visibility(false),
       using_egl_image(false),
       allow_partial_texture_updates(false),
@@ skipping 27 matching lines @@
     bitmap_ = make_scoped_ptr(new UIResourceBitmap(*request.bitmap_.get()));
   } else {
     bitmap_.reset();
   }
 
   return *this;
 }
 
 UIResourceRequest::~UIResourceRequest() {}
 
-bool LayerTreeHost::AnyLayerTreeHostInstanceExists() {
-  return s_num_layer_tree_instances > 0;
-}
-
 scoped_ptr<LayerTreeHost> LayerTreeHost::Create(
     LayerTreeHostClient* client,
     SharedBitmapManager* manager,
     const LayerTreeSettings& settings,
     scoped_refptr<base::SingleThreadTaskRunner> impl_task_runner) {
   scoped_ptr<LayerTreeHost> layer_tree_host(
       new LayerTreeHost(client, manager, settings));
   if (!layer_tree_host->Initialize(impl_task_runner))
     return scoped_ptr<LayerTreeHost>();
   return layer_tree_host.Pass();
 }
 
-static int s_next_tree_id = 1;
-
 LayerTreeHost::LayerTreeHost(LayerTreeHostClient* client,
                              SharedBitmapManager* manager,
                              const LayerTreeSettings& settings)
     : next_ui_resource_id_(1),
       animating_(false),
       needs_full_tree_sync_(true),
       needs_filter_context_(false),
       client_(client),
       source_frame_number_(0),
       rendering_stats_instrumentation_(RenderingStatsInstrumentation::Create()),
       micro_benchmark_controller_(this),
       output_surface_can_be_initialized_(true),
       output_surface_lost_(true),
       num_failed_recreate_attempts_(0),
       settings_(settings),
       debug_state_(settings.initial_debug_state),
       overdraw_bottom_height_(0.f),
       device_scale_factor_(1.f),
       visible_(true),
       page_scale_factor_(1.f),
       min_page_scale_factor_(1.f),
       max_page_scale_factor_(1.f),
       trigger_idle_updates_(true),
       background_color_(SK_ColorWHITE),
       has_transparent_background_(false),
       partial_texture_update_requests_(0),
       in_paint_layer_contents_(false),
       total_frames_used_for_lcd_text_metrics_(0),
-      tree_id_(s_next_tree_id++),
+      tree_id_(GetNextTreeId()),
       next_commit_forces_redraw_(false),
       shared_bitmap_manager_(manager) {
   if (settings_.accelerated_animation_enabled)
     animation_registrar_ = AnimationRegistrar::Create();
-  s_num_layer_tree_instances++;
   rendering_stats_instrumentation_->set_record_rendering_stats(
       debug_state_.RecordRenderingStats());
 }
 
 bool LayerTreeHost::Initialize(
     scoped_refptr<base::SingleThreadTaskRunner> impl_task_runner) {
   if (impl_task_runner.get())
     return InitializeProxy(ThreadProxy::Create(this, impl_task_runner));
   else
     return InitializeProxy(SingleThreadProxy::Create(this));
@@ skipping 21 matching lines @@
   overhang_ui_resource_.reset();
 
   if (root_layer_.get())
     root_layer_->SetLayerTreeHost(NULL);
 
   if (proxy_) {
     DCHECK(proxy_->IsMainThread());
     proxy_->Stop();
   }
 
-  s_num_layer_tree_instances--;
   RateLimiterMap::iterator it = rate_limiters_.begin();
   if (it != rate_limiters_.end())
     it->second->Stop();
 
   if (root_layer_.get()) {
     // The layer tree must be destroyed before the layer tree host. We've
     // made a contract with our animation controllers that the registrar
     // will outlive them, and we must make good.
     root_layer_ = NULL;
   }
@@ skipping 1088 matching lines @@
 
 bool LayerTreeHost::ScheduleMicroBenchmark(
     const std::string& benchmark_name,
     scoped_ptr<base::Value> value,
     const MicroBenchmark::DoneCallback& callback) {
   return micro_benchmark_controller_.ScheduleRun(
       benchmark_name, value.Pass(), callback);
 }
 
 }  // namespace cc