Expose global state variables for sampling tracing to WebKit

We are implementing TRACE_EVENT macros for sampling profiling. It works in the following mechanism:

- Chromium defines global state variables for sampling profiling. (i.e. g_trace_state0, g_trace_state1, g_trace_state2 in trace_event.h)

- WebKit gets the addresses of the global state variables at the initialization step. (i.e. EventTracer::initialize())

- WebKit updates the global states by using TRACE_EVENT_SAMPLING_STATE() macros every time WebKit changes its state. (e.g. DOM attribute getters/setters/methods)

- A sampling thread running in Chrome reads the global states periodically and visualizes the profiling results into about://tracing.

In this issue, we make a Chromium side change to implement a WebKit API to get the addresses of the global states.

The WebKit patch is here: https://bugs.webkit.org/show_bug.cgi?id=110932

Review URL: https://chromiumcodereview.appspot.com/12316146

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@186162 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 17 insertions, 1 deletions

diff --git a/webkit/glue/webkitplatformsupport_impl.cc b/webkit/glue/webkitplatformsupport_impl.cc
index 34e63d2..0064ce9 100644
--- a/webkit/glue/webkitplatformsupport_impl.cc
+++ b/webkit/glue/webkitplatformsupport_impl.cc
@@ -10,7 +10,6 @@
 
 #include "base/allocator/allocator_extension.h"
 #include "base/bind.h"
-#include "base/debug/trace_event.h"
 #include "base/memory/discardable_memory.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
@@ -453,6 +452,21 @@ const unsigned char* WebKitPlatformSupportImpl::getTraceCategoryEnabledFlag(
   return TRACE_EVENT_API_GET_CATEGORY_ENABLED(category_name);
 }
 
+long* WebKitPlatformSupportImpl::getTraceSamplingState(
+    const unsigned thread_bucket) {
+  switch(thread_bucket) {
+  case 0:
+    return reinterpret_cast<long*>(&TRACE_EVENT_API_THREAD_BUCKET(0));
+  case 1:
+    return reinterpret_cast<long*>(&TRACE_EVENT_API_THREAD_BUCKET(1));
+  case 2:
+    return reinterpret_cast<long*>(&TRACE_EVENT_API_THREAD_BUCKET(2));
+  default:
+    NOTREACHED() << "Unknown thread bucket type.";
+  }
+  return NULL;
+}
+
 void WebKitPlatformSupportImpl::addTraceEvent(
     char phase,
     const unsigned char* category_enabled,
diff --git a/webkit/glue/webkitplatformsupport_impl.h b/webkit/glue/webkitplatformsupport_impl.h
index 859309e..0f77447 100644
--- a/webkit/glue/webkitplatformsupport_impl.h
+++ b/webkit/glue/webkitplatformsupport_impl.h
@@ -6,6 +6,7 @@
 #define WEBKIT_PLATFORM_SUPPORT_IMPL_H_
 
 #include "base/compiler_specific.h"
+#include "base/debug/trace_event.h"
 #include "base/platform_file.h"
 #include "base/threading/thread_local_storage.h"
 #include "base/timer.h"
@@ -88,6 +89,7 @@ class WEBKIT_GLUE_EXPORT WebKitPlatformSupportImpl :
     const char* name, int sample, int boundary_value);
   virtual const unsigned char* getTraceCategoryEnabledFlag(
       const char* category_name);
+  virtual long* getTraceSamplingState(const unsigned thread_bucket);
   virtual void addTraceEvent(
       char phase,
       const unsigned char* category_enabled,