tracing: Add macros for generating 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 318 matching lines @@
                                                          &trace_event_flags); \
       trace_event_internal::AddTraceEventWithThreadIdAndTimestamp(            \
           phase, INTERNAL_TRACE_EVENT_UID(category_group_enabled), name,      \
           trace_event_trace_id.data(), thread_id,                             \
           base::TimeTicks::FromInternalValue(timestamp),                      \
           trace_event_flags | TRACE_EVENT_FLAG_EXPLICIT_TIMESTAMP,            \
           trace_event_internal::kNoId, ##__VA_ARGS__);                        \
     }                                                                         \
   } while (0)
 
+// Implementation detail: internal macro to enter and leave a context based on
+// the current scope.
+#define INTERNAL_TRACE_EVENT_SCOPED_CONTEXT(category_group, name, context) \
+  trace_event_internal::TraceScopedContext INTERNAL_TRACE_EVENT_UID(       \
+      scoped_trace)(category_group, name, context)
+
 namespace trace_event_internal {
 
 // Specify these values when the corresponding argument of AddTraceEvent is not
 // used.
 const int kZeroNumArgs = 0;
 const unsigned long long kNoId = 0;
 
 // TraceID encapsulates an ID that can either be an integer or pointer. Pointers
 // are by default mangled with the Process ID so that they are unlikely to
 // collide when the same pointer is used on different processes.
@@ skipping 527 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*;
+
+class TraceScopedContext {
+ public:
+  TraceScopedContext(const char* category_group,
+                     const char* name,
+                     TraceContext 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_;
+  DISALLOW_COPY_AND_ASSIGN(TraceScopedContext);
+};
+
 }  // namespace trace_event_internal
 
 namespace base {
 namespace trace_event {
 
+using trace_event_internal::TraceContext;
+
 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 10 matching lines @@
   const char* name_;
   IDType id_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceScopedTrackableObject);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_TRACE_EVENT_H_