Make tree id sequence in LayerTreeHost thread-safe.

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index d93e3d5e032e80c8cf353b672338904f832a16f2..bc346e86921d7758ac96848a0ec6aeeaa1906e7a 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -8,9 +8,11 @@
 #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"
@@ -41,7 +43,14 @@
 #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 {
@@ -89,10 +98,6 @@ UIResourceRequest& UIResourceRequest::operator=(
 
 UIResourceRequest::~UIResourceRequest() {}
 
-bool LayerTreeHost::AnyLayerTreeHostInstanceExists() {
-  return s_num_layer_tree_instances > 0;
-}
-
 scoped_ptr<LayerTreeHost> LayerTreeHost::Create(
     LayerTreeHostClient* client,
     SharedBitmapManager* manager,
@@ -105,8 +110,6 @@ scoped_ptr<LayerTreeHost> LayerTreeHost::Create(
   return layer_tree_host.Pass();
 }
 
-static int s_next_tree_id = 1;
-
 LayerTreeHost::LayerTreeHost(LayerTreeHostClient* client,
                              SharedBitmapManager* manager,
                              const LayerTreeSettings& settings)
@@ -135,12 +138,11 @@ LayerTreeHost::LayerTreeHost(LayerTreeHostClient* client,
       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());
 }
@@ -182,7 +184,6 @@ LayerTreeHost::~LayerTreeHost() {
     proxy_->Stop();
   }
 
-  s_num_layer_tree_instances--;
   RateLimiterMap::iterator it = rate_limiters_.begin();
   if (it != rate_limiters_.end())
     it->second->Stop();