Add a sampling tracing to RenderWidget::DoDeferredUpdate

base/debug/trace_event.h

 // 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.
 
 // This header file defines the set of trace_event macros without specifying
 // how the events actually get collected and stored. If you need to expose trace
 // events to some other universe, you can copy-and-paste this file as well as
 // trace_event.h, modifying the macros contained there as necessary for the
 // target platform. The end result is that multiple libraries can funnel events
 // through to a shared trace event collector.
@@ skipping 281 matching lines @@
     INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, \
         category_group, name, TRACE_EVENT_FLAG_COPY | scope, \
         arg1_name, arg1_val, arg2_name, arg2_val)
 
 // Sets the current sample state to the given category and name (both must be
 // constant strings). These states are intended for a sampling profiler.
 // Implementation note: we store category and name together because we don't
 // want the inconsistency/expense of storing two pointers.
 // |thread_bucket| is [0..2] and is used to statically isolate samples in one
 // thread from others.
-#define TRACE_EVENT_SAMPLE_STATE(thread_bucket, category, name)                \
-  TRACE_EVENT_API_ATOMIC_STORE(                                                \
-      TRACE_EVENT_API_THREAD_BUCKET(thread_bucket),                            \
+#define TRACE_EVENT_SAMPLING_STATE0(category, name) \
+    INTERNAL_TRACE_EVENT_SAMPLING_STATE(0, category, name)
+#define TRACE_EVENT_SAMPLING_STATE1(category, name) \
+    INTERNAL_TRACE_EVENT_SAMPLING_STATE(1, category, name)
+#define TRACE_EVENT_SAMPLING_STATE2(category, name) \
+    INTERNAL_TRACE_EVENT_SAMPLING_STATE(2, category, name)
+
+#define INTERNAL_TRACE_EVENT_SAMPLING_STATE(thread_bucket, category, name) \
+  TRACE_EVENT_API_ATOMIC_STORE(                                            \
+      TRACE_EVENT_API_THREAD_BUCKET(thread_bucket),                        \
       reinterpret_cast<TRACE_EVENT_API_ATOMIC_WORD>(category "\0" name));
 
 // Records a single BEGIN event called "name" immediately, with 0, 1 or 2
 // associated arguments. If the category is not enabled, then this
 // does nothing.
 // - category and name strings must have application lifetime (statics or
 //   literals). They may not include " chars.
 #define TRACE_EVENT_BEGIN0(category_group, name) \
     INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, \
         category_group, name, TRACE_EVENT_FLAG_NONE)
@@ skipping 441 matching lines @@
 #define TRACE_EVENT_API_CLASS_EXPORT BASE_EXPORT
 
 // Not supported in split-dll build. http://crbug.com/237249
 #if !defined(CHROME_SPLIT_DLL)
 // The thread buckets for the sampling profiler.
 TRACE_EVENT_API_CLASS_EXPORT extern TRACE_EVENT_API_ATOMIC_WORD g_trace_state0;
 TRACE_EVENT_API_CLASS_EXPORT extern TRACE_EVENT_API_ATOMIC_WORD g_trace_state1;
 TRACE_EVENT_API_CLASS_EXPORT extern TRACE_EVENT_API_ATOMIC_WORD g_trace_state2;
 #define TRACE_EVENT_API_THREAD_BUCKET(thread_bucket)                           \
   g_trace_state##thread_bucket
+
+// TraceEventSamplingState0Scope records the current sampling state
+// and sets a new sampling state. When the scope exists, it restores
+// the sampling state having recorded.
+class TraceEventSamplingState0Scope {
+public:
+    TraceEventSamplingState0Scope(const char* category_and_name)
+    {
+        previousState0_ = TraceEventSamplingState0Scope::current();
+        TraceEventSamplingState0Scope::forceCurrent(category_and_name);
+    }
+
+    ~TraceEventSamplingState0Scope()
+    {
+        TraceEventSamplingState0Scope::forceCurrent(previousState0_);
+    }
+
+    static inline const char* current()

[scottmg, 2013/07/03 02:16:10]

In chromium code, these should be Current()

[haraken, 2013/07/03 02:38:50]

Done.

+    {
+        return reinterpret_cast<const char*>(TRACE_EVENT_API_ATOMIC_LOAD(
+          TRACE_EVENT_API_THREAD_BUCKET(0)));
+    }
+
+    static inline void forceCurrent(const char* category_and_name)

[scottmg, 2013/07/03 02:16:10]

and ForceCurrent. Maybe just "Set" would be fine though?

[haraken, 2013/07/03 02:38:50]

Done.

+    {
+        TRACE_EVENT_API_ATOMIC_STORE(
+          TRACE_EVENT_API_THREAD_BUCKET(0),
+          reinterpret_cast<TRACE_EVENT_API_ATOMIC_WORD>(
+            const_cast<char*>(category_and_name)));
+    }
+
+private:
+    const char* previousState0_;

[scottmg, 2013/07/03 02:16:10]

and previous_state0_

[haraken, 2013/07/03 02:38:50]

Done.

+};
 #endif
 
 ////////////////////////////////////////////////////////////////////////////////
 
 // Implementation detail: trace event macros create temporary variables
 // to keep instrumentation overhead low. These macros give each temporary
 // variable a unique name based on the line number to prevent name collissions.
 #define INTERNAL_TRACE_EVENT_UID3(a,b) \
     trace_event_unique_##a##b
 #define INTERNAL_TRACE_EVENT_UID2(a,b) \
@@ skipping 691 matching lines @@
   const char* name_;
   IDType id_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceScopedTrackableObject);
 };
 
 } // namespace debug
 } // namespace base
 
 #endif /* BASE_DEBUG_TRACE_EVENT_H_ */