Add OnBeforeTraceLogDisabled notification to EnabledStateObserver

base/trace_event/trace_log.h

 // Copyright 2015 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_TRACE_EVENT_TRACE_LOG_H_
 #define BASE_TRACE_EVENT_TRACE_LOG_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 95 matching lines @@
   // disabled. This can be used to tie into other library's tracing systems
   // on-demand.
   class BASE_EXPORT EnabledStateObserver {
    public:
     virtual ~EnabledStateObserver() = default;
 
     // Called just after the tracing system becomes enabled, outside of the
     // |lock_|. TraceLog::IsEnabled() is true at this point.
     virtual void OnTraceLogEnabled() = 0;
 
+    // Called just before the tracing system disables, outside of the |lock_|.
+    // TraceLog::IsEnabled() is true at this point. It is still possible to
+    // emit trace events from the observer.
+    virtual void OnBeforeTraceLogDisabled() {}
+
     // Called just after the tracing system disables, outside of the |lock_|.
     // TraceLog::IsEnabled() is false at this point.
     virtual void OnTraceLogDisabled() = 0;
   };
   void AddEnabledStateObserver(EnabledStateObserver* listener);
   void RemoveEnabledStateObserver(EnabledStateObserver* listener);
   bool HasEnabledStateObserver(EnabledStateObserver* listener) const;
 
   // Asynchronous enabled state listeners. When tracing is enabled or disabled,
   // for each observer, a task for invoking its appropriate callback is posted
@@ skipping 347 matching lines @@
   static const InternalTraceOptions kInternalRecordUntilFull;
   static const InternalTraceOptions kInternalRecordContinuously;
   static const InternalTraceOptions kInternalEchoToConsole;
   static const InternalTraceOptions kInternalEnableSampling;
   static const InternalTraceOptions kInternalRecordAsMuchAsPossible;
   static const InternalTraceOptions kInternalEnableArgumentFilter;
 
   // This lock protects TraceLog member accesses (except for members protected
   // by thread_info_lock_) from arbitrary threads.
   mutable Lock lock_;
+  // This lock protects TraceLog::SetDisable from being entered by multiple
+  // threads. The generic |lock_| could be unlocked during iterating over
+  // EnabledStateObserver's.
+  mutable Lock disabling_lock_;
   // This lock protects accesses to thread_names_, thread_event_start_times_
   // and thread_colors_.
   Lock thread_info_lock_;
   Mode mode_;
   int num_traces_recorded_;
   std::unique_ptr<TraceBuffer> logged_events_;
   std::vector<std::unique_ptr<TraceEvent>> metadata_events_;
   subtle::AtomicWord /* EventCallback */ event_callback_;
   bool dispatching_to_observer_list_;
   std::vector<EnabledStateObserver*> enabled_state_observer_list_;
@@ skipping 54 matching lines @@
   subtle::AtomicWord generation_;
   bool use_worker_thread_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceLog);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_TRACE_LOG_H_