tracing: Introduce API for composite IDs

base/trace_event/trace_event.h

Index: base/trace_event/trace_event.h
diff --git a/base/trace_event/trace_event.h b/base/trace_event/trace_event.h
index 0299ddd0cb70356313e3c95fa195b09e50d36246..649fd9b637c399d1b61278c7ffff0cb0ce697a07 100644
--- a/base/trace_event/trace_event.h
+++ b/base/trace_event/trace_event.h
@@ -45,10 +45,14 @@
 // By default, trace IDs are eventually converted to a single 64-bit number. Use
 // this macro to add a scope string.
 #define TRACE_ID_WITH_SCOPE(scope, id) \
-    trace_event_internal::TraceID::WithScope(scope, id)
-
-#define TRACE_ID_GLOBAL(id) trace_event_internal::TraceID::GlobalId(id)
-#define TRACE_ID_LOCAL(id) trace_event_internal::TraceID::LocalId(id)
+  trace_event_internal::TraceID::MakeScopedID(scope, id)
+// Can be nested within TRACE_ID_WITH_SCOPE macro.
+#define TRACE_ID_GLOBAL(id) trace_event_internal::TraceID::MakeGlobalID(id)
+// Can be nested within TRACE_ID_WITH_SCOPE macro.
+#define TRACE_ID_LOCAL(id) trace_event_internal::TraceID::MakeLocalID(id)
+// Can be nested within TRACE_ID_{LOCAL, GLOBAL, WITH_SCOPE} macros.
+#define TRACE_ID_COMPOSITE(prefix, id) \
+  trace_event_internal::TraceID::CompositeID(prefix, id)
 
 #define TRACE_EVENT_API_CURRENT_THREAD_ID \
   static_cast<int>(base::PlatformThread::CurrentId())
@@ -408,38 +412,57 @@ const unsigned long long kNoId = 0;
 // collide when the same pointer is used on different processes.
 class BASE_EXPORT TraceID {
  public:
-  // Can be combined with WithScope.
-  class LocalId {
+  class CompositeID {
+   public:
+    CompositeID(unsigned long long prefix, unsigned long long raw_id)
+        : prefix_(prefix), raw_id_(raw_id) {}
+
+    void set_scope(const char* scope) { scope_ = scope; }
+
+    void set_id_flags(unsigned int id_flags) { id_flags_ = id_flags; }
+
+    const char* scope() const { return scope_; }
+    unsigned long long prefix() const { return prefix_; }
+    unsigned long long raw_id() const { return raw_id_; }
+    unsigned int id_flags() const { return id_flags_; }
+
+   private:
+    const char* scope_ = nullptr;
+    unsigned long long prefix_;
+    unsigned long long raw_id_;
+    unsigned int id_flags_ = TRACE_EVENT_FLAG_HAS_ID;
+  };
+
+  class LocalID {
    public:
-    explicit LocalId(unsigned long long raw_id) : raw_id_(raw_id) {}
+    explicit LocalID(unsigned long long raw_id) : raw_id_(raw_id) {}
     unsigned long long raw_id() const { return raw_id_; }
    private:
     unsigned long long raw_id_;
   };
 
-  // Can be combined with WithScope.
-  class GlobalId {
+  class GlobalID {
    public:
-    explicit GlobalId(unsigned long long raw_id) : raw_id_(raw_id) {}
+    explicit GlobalID(unsigned long long raw_id) : raw_id_(raw_id) {}
     unsigned long long raw_id() const { return raw_id_; }
    private:
     unsigned long long raw_id_;
   };
 
-  class WithScope {
+  class ScopedID {
    public:
-    WithScope(const char* scope, unsigned long long raw_id)
+    ScopedID(const char* scope, unsigned long long raw_id)
         : scope_(scope), raw_id_(raw_id) {}
-    WithScope(const char* scope, LocalId local_id)
+    ScopedID(const char* scope, LocalID local_id)
         : scope_(scope), raw_id_(local_id.raw_id()) {
       id_flags_ = TRACE_EVENT_FLAG_HAS_LOCAL_ID;
     }
-    WithScope(const char* scope, GlobalId global_id)
+    ScopedID(const char* scope, GlobalID global_id)
         : scope_(scope), raw_id_(global_id.raw_id()) {
       id_flags_ = TRACE_EVENT_FLAG_HAS_GLOBAL_ID;
     }
-    unsigned long long raw_id() const { return raw_id_; }
     const char* scope() const { return scope_; }
+    unsigned long long raw_id() const { return raw_id_; }
     unsigned int id_flags() const { return id_flags_; }
    private:
     const char* scope_ = nullptr;
@@ -447,7 +470,36 @@ class BASE_EXPORT TraceID {
     unsigned int id_flags_ = TRACE_EVENT_FLAG_HAS_ID;
   };
 
-  // DEPRECATED: consider using LocalId or GlobalId, instead.
+  static inline CompositeID MakeLocalID(CompositeID& composite_id) {
+    composite_id.set_id_flags(TRACE_EVENT_FLAG_HAS_LOCAL_ID);
+    return composite_id;
+  }
+
+  static inline LocalID MakeLocalID(unsigned long long raw_id) {
+    return LocalID(raw_id);
+  }
+
+  static inline CompositeID MakeGlobalID(CompositeID& composite_id) {
+    composite_id.set_id_flags(TRACE_EVENT_FLAG_HAS_GLOBAL_ID);
+    return composite_id;
+  }
+
+  static inline GlobalID MakeGlobalID(unsigned long long raw_id) {
+    return GlobalID(raw_id);
+  }
+
+  static inline CompositeID MakeScopedID(const char* scope,
+                                         CompositeID& composite_id) {

[caseq, 2016/11/21 19:47:20]

const ComositeID&

[chiniforooshan, 2016/11/21 21:12:15]

But composite_id is actually modified in this function.

+    composite_id.set_scope(scope);
+    return composite_id;
+  }
+
+  template <typename T>
+  static inline ScopedID MakeScopedID(const char* scope, T raw_id) {

[caseq, 2016/11/21 19:47:20]

why do we need it to be template? looks like we only would pass the template
parameter to a non-template ScopedID constructor that expects unsigned long
long.

[chiniforooshan, 2016/11/21 21:12:15]

I think you missed the other two constructors :) ScopedID constructor"s" expect
unsgined long long, LocalID, or GlobalID.

+    return ScopedID(scope, raw_id);
+  }
+
+  // DEPRECATED: consider using LocalID or GlobalID, instead.
   class DontMangle {
    public:
     explicit DontMangle(const void* raw_id)
@@ -473,7 +525,7 @@ class BASE_EXPORT TraceID {
     unsigned long long raw_id_;
   };
 
-  // DEPRECATED: consider using LocalId or GlobalId, instead.
+  // DEPRECATED: consider using LocalID or GlobalID, instead.
   class ForceMangle {
    public:
     explicit ForceMangle(unsigned long long raw_id) : raw_id_(raw_id) {}
@@ -519,17 +571,27 @@ class BASE_EXPORT TraceID {
       : raw_id_(static_cast<unsigned long long>(raw_id)) {}
   TraceID(signed char raw_id)
       : raw_id_(static_cast<unsigned long long>(raw_id)) {}
-  TraceID(LocalId raw_id) : raw_id_(raw_id.raw_id()) {
+  TraceID(LocalID local_id) : raw_id_(local_id.raw_id()) {
     id_flags_ = TRACE_EVENT_FLAG_HAS_LOCAL_ID;
   }
-  TraceID(GlobalId raw_id) : raw_id_(raw_id.raw_id()) {
+  TraceID(GlobalID global_id) : raw_id_(global_id.raw_id()) {
     id_flags_ = TRACE_EVENT_FLAG_HAS_GLOBAL_ID;
   }
-  TraceID(WithScope scoped_id) : scope_(scoped_id.scope()),
-      raw_id_(scoped_id.raw_id()), id_flags_(scoped_id.id_flags()) {}
+  TraceID(ScopedID scoped_id)
+      : scope_(scoped_id.scope()),
+        raw_id_(scoped_id.raw_id()),
+        id_flags_(scoped_id.id_flags()) {}
+  TraceID(CompositeID composite_id)
+      : scope_(composite_id.scope()),
+        has_prefix_(true),
+        prefix_(composite_id.prefix()),
+        raw_id_(composite_id.raw_id()),
+        id_flags_(composite_id.id_flags()) {}
 
-  unsigned long long raw_id() const { return raw_id_; }
   const char* scope() const { return scope_; }
+  bool has_prefix() const { return has_prefix_; }
+  unsigned long long prefix() const { return prefix_; }
+  unsigned long long raw_id() const { return raw_id_; }
   unsigned int id_flags() const { return id_flags_; }
 
   std::unique_ptr<base::trace_event::ConvertableToTraceFormat>
@@ -537,6 +599,8 @@ class BASE_EXPORT TraceID {
 
  private:
   const char* scope_ = nullptr;
+  bool has_prefix_ = false;
+  unsigned long long prefix_;
   unsigned long long raw_id_;
   unsigned int id_flags_ = TRACE_EVENT_FLAG_HAS_ID;
 };