Expose global state variables for sampling tracing to WebKit

webkit/glue/webkitplatformsupport_impl.cc

 // 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.
 
 #include "webkit/glue/webkitplatformsupport_impl.h"
 
 #include <math.h>
 
 #include <vector>
 
 #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"
 #include "base/message_loop.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/stats_counters.h"
 #include "base/platform_file.h"
 #include "base/process_util.h"
 #include "base/rand_util.h"
 #include "base/string_number_conversions.h"
@@ skipping 422 matching lines @@
           boundary_value + 1, base::HistogramBase::kUmaTargetedHistogramFlag);
   DCHECK_EQ(name, counter->histogram_name());
   counter->Add(sample);
 }
 
 const unsigned char* WebKitPlatformSupportImpl::getTraceCategoryEnabledFlag(
     const char* category_name) {
   return TRACE_EVENT_API_GET_CATEGORY_ENABLED(category_name);
 }
 
+TRACE_EVENT_API_ATOMIC_WORD* WebKitPlatformSupportImpl::getTraceSamplingState(
+    const unsigned thread_bucket) {
+  switch(thread_bucket) {

[abarth-chromium, 2013/02/27 02:58:00]

Is this really better than a branch +
TRACE_EVENT_API_THREAD_BUCKET(thread_bucket)

[haraken, 2013/02/27 03:29:55]

I cannot use it because it results in 'g_trace_statethread_bucket', not
'g_trace_state0'...

(This method is called only three times at the initialization step, so the
performance wouldn't be a problem.)

+  case 0:
+    return reinterpret_cast<TRACE_EVENT_API_ATOMIC_WORD*>(
+        &TRACE_EVENT_API_THREAD_BUCKET(0));
+  case 1:
+    return reinterpret_cast<TRACE_EVENT_API_ATOMIC_WORD*>(
+        &TRACE_EVENT_API_THREAD_BUCKET(1));
+  case 2:
+    return reinterpret_cast<TRACE_EVENT_API_ATOMIC_WORD*>(
+        &TRACE_EVENT_API_THREAD_BUCKET(2));
+  default:
+    NOTREACHED() << "Unknown thread bucket type.";
+  }
+  return NULL;
+}
+
 void WebKitPlatformSupportImpl::addTraceEvent(
     char phase,
     const unsigned char* category_enabled,
     const char* name,
     unsigned long long id,
     int num_args,
     const char** arg_names,
     const unsigned char* arg_types,
     const unsigned long long* arg_values,
     unsigned char flags) {
@@ skipping 486 matching lines @@
     return NULL;
   scoped_ptr<WebDiscardableMemoryImpl> discardable(
       new WebDiscardableMemoryImpl());
   if (discardable->InitializeAndLock(bytes))
     return discardable.release();
   return NULL;
 }
 
 
 }  // namespace webkit_glue