Enable overlapping, usage counted SetEnabled()/SetDisabled() for TraceLog

base/debug/trace_event_impl.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.
 
 
 #ifndef BASE_DEBUG_TRACE_EVENT_IMPL_H_
 #define BASE_DEBUG_TRACE_EVENT_IMPL_H_
 
 #include "build/build_config.h"
 
@@ skipping 188 matching lines @@
 
   // Retieves the categories set via a prior call to SetEnabled(). Only
   // meaningful if |IsEnabled()| is true.
   void GetEnabledTraceCategories(std::vector<std::string>* included_out,
                                  std::vector<std::string>* excluded_out);
 
   // Disable tracing for all categories.
   void SetDisabled();
   // Helper method to enable/disable tracing for all categories.
   void SetEnabled(bool enabled);
-  bool IsEnabled() { return enabled_; }
+  bool IsEnabled() { return !!enable_count_; }
 
 #if defined(OS_ANDROID)
   static void InitATrace();
 #endif
 
   // Enabled state listeners give a callback when tracing is enabled or
   // disabled. This can be used to tie into other library's tracing systems
   // on-demand.
   class EnabledStateChangedObserver {
    public:
@@ skipping 140 matching lines @@
                     const unsigned char* arg_types,
                     const unsigned long long* arg_values);
   void AddClockSyncMetadataEvents();
   static void ApplyATraceEnabledFlag(unsigned char* category_enabled);
 #endif
 
   // TODO(nduca): switch to per-thread trace buffers to reduce thread
   // synchronization.
   // This lock protects TraceLog member accesses from arbitrary threads.
   Lock lock_;
-  bool enabled_;
+  int enable_count_;
   NotificationCallback notification_callback_;
   std::vector<TraceEvent> logged_events_;
   std::vector<std::string> included_categories_;
   std::vector<std::string> excluded_categories_;
   bool dispatching_to_observer_list_;
   ObserverList<EnabledStateChangedObserver> enabled_state_observer_list_;
 
   base::hash_map<int, std::string> thread_names_;
 
   // XORed with TraceID to make it unlikely to collide with other processes.
   unsigned long long process_id_hash_;
 
   int process_id_;
 
   TimeDelta time_offset_;
 
   // Allow tests to wake up when certain events occur.
   const unsigned char* watch_category_;
   std::string watch_event_name_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceLog);
 };
 
 }  // namespace debug
 }  // namespace base
 
 #endif  // BASE_DEBUG_TRACE_EVENT_IMPL_H_