base: Add scope support to context trace events

base/trace_event/trace_event.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_TRACE_EVENT_TRACE_EVENT_H_
 #define BASE_TRACE_EVENT_TRACE_EVENT_H_
 
 // This header file defines implementation details of how the trace macros in
 // trace_event_common.h collect and store trace events. Anything not
 // implementation-specific should go in trace_macros_common.h instead of here.
@@ skipping 922 matching lines @@
     TRACE_EVENT_API_ATOMIC_STORE(
       g_trace_state[BucketNumber],
       reinterpret_cast<TRACE_EVENT_API_ATOMIC_WORD>(
         const_cast<char*>(category_and_name)));
   }
 
  private:
   const char* previous_state_;
 };
 
-using TraceContext = const void*;
+using TraceContext = trace_event_internal::TraceID;

[chiniforooshan, 2016/01/28 20:19:23]

Where is this used?

[Sami, 2016/02/01 17:45:58]

The current code doesn't use it because all contexts are created inline, but I'm
planning to use it for associating a trace context with a task queue.

 
 class TraceScopedContext {
  public:
   TraceScopedContext(const char* category_group,
                      const char* name,
-                     TraceContext context)
+                     trace_event_internal::TraceID::DontMangle context)
       : category_group_(category_group), name_(name), context_(context) {
     TRACE_EVENT_ENTER_CONTEXT(category_group_, name_, context_);
   }
 
   ~TraceScopedContext() {
     TRACE_EVENT_LEAVE_CONTEXT(category_group_, name_, context_);
   }
 
  private:
   const char* category_group_;
   const char* name_;
-  TraceContext context_;
+  trace_event_internal::TraceID::DontMangle context_;
   DISALLOW_COPY_AND_ASSIGN(TraceScopedContext);
 };
 
 }  // namespace trace_event_internal
 
 namespace base {
 namespace trace_event {
 
 using trace_event_internal::TraceContext;

[chiniforooshan, 2016/01/28 20:19:22]

or this?

[Sami, 2016/02/01 17:45:58]

Well spotted, this isn't needed anymore.

 
 template<typename IDType> class TraceScopedTrackableObject {
  public:
   TraceScopedTrackableObject(const char* category_group, const char* name,
       IDType id)
     : category_group_(category_group),
       name_(name),
       id_(id) {
     TRACE_EVENT_OBJECT_CREATED_WITH_ID(category_group_, name_, id_);
   }
@@ skipping 11 matching lines @@
   const char* name_;
   IDType id_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceScopedTrackableObject);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_TRACE_EVENT_H_