Avoid emptry tracing callbacks when possible.

base/trace_event/trace_event_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 "base/trace_event/trace_event_impl.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/base_switches.h"
@@ skipping 1797 matching lines @@
 // Usually it runs on a different thread.
 void TraceLog::ConvertTraceEventsToTraceFormat(
     scoped_ptr<TraceBuffer> logged_events,
     const OutputCallback& flush_output_callback,
     const TraceEvent::ArgumentFilterPredicate& argument_filter_predicate) {
   if (flush_output_callback.is_null())
     return;
 
   // The callback need to be called at least once even if there is no events
   // to let the caller know the completion of flush.
-  bool has_more_events = true;
-  do {
-    scoped_refptr<RefCountedString> json_events_str_ptr =
-        new RefCountedString();
-
-    while (json_events_str_ptr->size() < kTraceEventBufferSizeInBytes) {
-      const TraceBufferChunk* chunk = logged_events->NextChunk();
-      has_more_events = chunk != NULL;
-      if (!chunk)
-        break;
-      for (size_t j = 0; j < chunk->size(); ++j) {
-        if (json_events_str_ptr->size())
-          json_events_str_ptr->data().append(",\n");
-        chunk->GetEventAt(j)->AppendAsJSON(&(json_events_str_ptr->data()),
-                                           argument_filter_predicate);
+  scoped_refptr<RefCountedString> json_events_str_ptr = new RefCountedString();
+  while (const TraceBufferChunk* chunk = logged_events->NextChunk()) {
+    for (size_t j = 0; j < chunk->size(); ++j) {
+      size_t size = json_events_str_ptr->size();
+      if (size > kTraceEventBufferSizeInBytes) {
+        flush_output_callback.Run(json_events_str_ptr, true);
+        json_events_str_ptr = new RefCountedString();
+      } else if (size) {
+        json_events_str_ptr->data().append(",\n");
       }
+      chunk->GetEventAt(j)->AppendAsJSON(&(json_events_str_ptr->data()),
+                                         argument_filter_predicate);
     }
-    flush_output_callback.Run(json_events_str_ptr, has_more_events);
-  } while (has_more_events);
+  }
+  flush_output_callback.Run(json_events_str_ptr, false);
 }
 
 void TraceLog::FinishFlush(int generation) {
   scoped_ptr<TraceBuffer> previous_logged_events;
   OutputCallback flush_output_callback;
   TraceEvent::ArgumentFilterPredicate argument_filter_predicate;
 
   if (!CheckGeneration(generation))
     return;
 
@@ skipping 639 matching lines @@
 }
 
 ScopedTraceBinaryEfficient::~ScopedTraceBinaryEfficient() {
   if (*category_group_enabled_) {
     TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(category_group_enabled_,
                                                 name_, event_handle_);
   }
 }
 
 }  // namespace trace_event_internal