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) \

[nduca, 2013/07/03 05:34:24]

can you provide some explanation on why the rename was done? I dont review
blink, otherwise I would have asked that there as well. I wonder, having not
looked at this API in a few months, why there isn't the word SET in there
somewhere. Also, after not looking for a while, the 0 suffix makes me think this
is arguments, e.g. TRACE_EVENT0. I know its not, so I start wondering should
this just be

TARCE_EVENT_SET_SAMPLEING_STATE_FOR_BUCKET(bucket_number, category, name)

Its long, but its very obvious that way.

[haraken, 2013/07/03 07:33:15]

Makes sense. I renamed it to TARCE_EVENT_SET_SAMPLEING_STATE_FOR_BUCKET. I'll do
the same rename in Blink accordingly.

+    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 {

[nduca, 2013/07/03 05:34:24]

Can we templatize this so that this works for 1,2 buckets as well?

[haraken, 2013/07/03 07:33:15]

Done.

+ public:
+  TraceEventSamplingState0Scope(const char* category_and_name) {

[nduca, 2013/07/03 05:34:24]

we prefer people not use the scope objects directly --- see how TRACE_EVENT0
calls INTERNAL_xxx_SCOPED, which then instantiates the scoped object itself.

[haraken, 2013/07/03 07:33:15]

Done.

+    previous_state0_ = TraceEventSamplingState0Scope::Current();
+    TraceEventSamplingState0Scope::Set(category_and_name);
+  }
+
+  ~TraceEventSamplingState0Scope() {
+    TraceEventSamplingState0Scope::Set(previous_state0_);
+  }
+
+  static inline const char* Current() {
+    return reinterpret_cast<const char*>(TRACE_EVENT_API_ATOMIC_LOAD(
+      TRACE_EVENT_API_THREAD_BUCKET(0)));
+  }
+
+  static inline void Set(const char* category_and_name) {
+    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* previous_state0_;
+};
 #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_ */