Implement tracing interface for v8

src/tracing/trace-event.h

+// Copyright 2015 the V8 project 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 SRC_TRACING_TRACE_EVENT_H_
+#define SRC_TRACING_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.
+
+#include "include/v8-tracing.h"
+#include "src/tracing/trace-event-common.h"
+
+// By default, const char* argument values are assumed to have long-lived scope
+// and will not be copied. Use this macro to force a const char* to be copied.
+#define TRACE_STR_COPY(str) v8::internal::tracing::TraceStringWithCopy(str)
+
+// By default, uint64 ID argument values are not mangled with the Process ID in
+// TRACE_EVENT_ASYNC macros. Use this macro to force Process ID mangling.
+#define TRACE_ID_MANGLE(id) v8::internal::tracing::TraceID::ForceMangle(id)
+
+// By default, pointers are mangled with the Process ID in TRACE_EVENT_ASYNC
+// macros. Use this macro to prevent Process ID mangling.
+#define TRACE_ID_DONT_MANGLE(id) v8::internal::tracing::TraceID::DontMangle(id)
+
+// Sets the current sample state to the given category and name (both must be
+// constant strings). These states are intended for a sampling profiler.
+// Implementation note: we store category and name together because we don't
+// want the inconsistency/expense of storing two pointers.
+// |thread_bucket| is [0..2] and is used to statically isolate samples in one
+// thread from others.
+#define TRACE_EVENT_SET_SAMPLING_STATE_FOR_BUCKET(bucket_number, category, \
+                                                  name)                    \
+  v8::internal::tracing::TraceEventSamplingStateScope<bucket_number>::Set( \
+      category "\0" name)
+
+// Returns a current sampling state of the given bucket.
+#define TRACE_EVENT_GET_SAMPLING_STATE_FOR_BUCKET(bucket_number) \
+  v8::internal::tracing::TraceEventSamplingStateScope<bucket_number>::Current()
+
+// Creates a scope of a sampling state of the given bucket.
+//
+// {  // The sampling state is set within this scope.
+//    TRACE_EVENT_SAMPLING_STATE_SCOPE_FOR_BUCKET(0, "category", "name");
+//    ...;
+// }
+#define TRACE_EVENT_SCOPED_SAMPLING_STATE_FOR_BUCKET(bucket_number, category, \
+                                                     name)                    \
+  trace_event_internal::TraceEventSamplingStateScope<bucket_number>           \
+      traceEventSamplingScope(category "\0" name);
+
+
+#define INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE() \
+  *INTERNAL_TRACE_EVENT_UID(category_group_enabled) &                    \
+      (EventTracer::kEnabledForRecording_CategoryGroupEnabledFlags |     \
+       EventTracer::kEnabledForEventCallback_CategoryGroupEnabledFlags)
+
+// The following macro has no implementation, but it needs to exist since
+// it gets called from scoped trace events. It cannot call UNIMPLEMENTED()
+// since an empty implementation is a valid one.
+#define INTERNAL_TRACE_MEMORY(category, name)
+
+////////////////////////////////////////////////////////////////////////////////
+// Implementation specific tracing API definitions.
+
+// Get a pointer to the enabled state of the given trace category. Only
+// long-lived literal strings should be given as the category group. The
+// returned pointer can be held permanently in a local static for example. If
+// the unsigned char is non-zero, tracing is enabled. If tracing is enabled,
+// TRACE_EVENT_API_ADD_TRACE_EVENT can be called. It's OK if tracing is disabled
+// between the load of the tracing state and the call to
+// TRACE_EVENT_API_ADD_TRACE_EVENT, because this flag only provides an early out
+// for best performance when tracing is disabled.
+// const uint8_t*
+//     TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(const char* category_group)
+#define TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED \
+  EventTracer::GetInstance()->GetCategoryGroupEnabled
+
+// Get the number of times traces have been recorded. This is used to implement
+// the TRACE_EVENT_IS_NEW_TRACE facility.
+// unsigned int TRACE_EVENT_API_GET_NUM_TRACES_RECORDED()
+#define TRACE_EVENT_API_GET_NUM_TRACES_RECORDED \
+  EventTracer::GetInstance()->getNumTracesRecorded
+
+// Add a trace event to the platform tracing system.
+// EventTracer::Handle TRACE_EVENT_API_ADD_TRACE_EVENT(
+//                    char phase,
+//                    const uint8_t* category_group_enabled,
+//                    const char* name,
+//                    uint64_t id,
+//                    uint64_t context_id,
+//                    uint64_t bind_id,
+//                    int num_args,
+//                    const char** arg_names,
+//                    const uint8_t* arg_types,
+//                    const uint64_t* arg_values,
+//                    unsigned int flags)
+#define TRACE_EVENT_API_ADD_TRACE_EVENT \
+  EventTracer::GetInstance()->AddTraceEvent
+
+// Set the duration field of a COMPLETE trace event.
+// void TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(
+//     const uint8_t* category_group_enabled,
+//     const char* name,
+//     EventTracer::Handle id)
+#define TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION \
+  EventTracer::GetInstance()->UpdateTraceEventDuration
+
+// Defines atomic operations used internally by the tracing system.
+#define TRACE_EVENT_API_ATOMIC_WORD v8::base::AtomicWord
+#define TRACE_EVENT_API_ATOMIC_LOAD(var) v8::base::NoBarrier_Load(&(var))
+#define TRACE_EVENT_API_ATOMIC_STORE(var, value) \
+  v8::base::NoBarrier_Store(&(var), (value))
+
+// The thread buckets for the sampling profiler.
+extern TRACE_EVENT_API_ATOMIC_WORD g_trace_state[3];
+
+#define TRACE_EVENT_API_THREAD_BUCKET(thread_bucket) \
+  g_trace_state[thread_bucket]
+
+////////////////////////////////////////////////////////////////////////////////
+
+// Implementation detail: trace event macros create temporary variables
+// to keep instrumentation overhead low. These macros give each temporary
+// variable a unique name based on the line number to prevent name collisions.
+#define INTERNAL_TRACE_EVENT_UID3(a, b) trace_event_unique_##a##b
+#define INTERNAL_TRACE_EVENT_UID2(a, b) INTERNAL_TRACE_EVENT_UID3(a, b)
+#define INTERNAL_TRACE_EVENT_UID(name_prefix) \
+  INTERNAL_TRACE_EVENT_UID2(name_prefix, __LINE__)
+
+// Implementation detail: internal macro to create static category.
+// No barriers are needed, because this code is designed to operate safely
+// even when the unsigned char* points to garbage data (which may be the case
+// on processors without cache coherency).
+#define INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO_CUSTOM_VARIABLES(             \
+    category_group, atomic, category_group_enabled)                          \
+  category_group_enabled =                                                   \
+      reinterpret_cast<const uint8_t*>(TRACE_EVENT_API_ATOMIC_LOAD(atomic)); \
+  if (!category_group_enabled) {                                             \
+    category_group_enabled =                                                 \
+        TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(category_group);          \
+    TRACE_EVENT_API_ATOMIC_STORE(                                            \
+        atomic, reinterpret_cast<TRACE_EVENT_API_ATOMIC_WORD>(               \
+                    category_group_enabled));                                \
+  }
+
+#define INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group)             \
+  static TRACE_EVENT_API_ATOMIC_WORD INTERNAL_TRACE_EVENT_UID(atomic) = 0; \
+  const uint8_t* INTERNAL_TRACE_EVENT_UID(category_group_enabled);         \
+  INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO_CUSTOM_VARIABLES(                 \
+      category_group, INTERNAL_TRACE_EVENT_UID(atomic),                    \
+      INTERNAL_TRACE_EVENT_UID(category_group_enabled));
+
+// Implementation detail: internal macro to create static category and add
+// event if the category is enabled.
+#define INTERNAL_TRACE_EVENT_ADD(phase, category_group, name, flags, ...)    \
+  do {                                                                       \
+    INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group);                  \
+    if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) {  \
+      v8::internal::tracing::AddTraceEvent(                                  \
+          phase, INTERNAL_TRACE_EVENT_UID(category_group_enabled), name,     \
+          v8::internal::tracing::kNoId, v8::internal::tracing::kNoId, flags, \
+          ##__VA_ARGS__);                                                    \
+    }                                                                        \
+  } while (0)
+
+// Implementation detail: internal macro to create static category and add begin
+// event if the category is enabled. Also adds the end event when the scope
+// ends.
+#define INTERNAL_TRACE_EVENT_ADD_SCOPED(category_group, name, ...)          \
+  INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group);                   \
+  v8::internal::tracing::ScopedTracer INTERNAL_TRACE_EVENT_UID(tracer);     \
+  if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) {   \
+    EventTracer::Handle h = v8::internal::tracing::AddTraceEvent(           \
+        TRACE_EVENT_PHASE_COMPLETE,                                         \
+        INTERNAL_TRACE_EVENT_UID(category_group_enabled), name,             \
+        v8::internal::tracing::kNoId, TRACE_EVENT_FLAG_NONE,                \
+        v8::internal::tracing::kNoId, ##__VA_ARGS__);                       \
+    INTERNAL_TRACE_EVENT_UID(tracer)                                        \
+        .Initialize(INTERNAL_TRACE_EVENT_UID(category_group_enabled), name, \
+                    h);                                                     \
+  }
+
+#define INTERNAL_TRACE_EVENT_ADD_SCOPED_WITH_FLOW(category_group, name,     \
+                                                  bind_id, flow_flags, ...) \
+  INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group);                   \
+  v8::internal::tracing::ScopedTracer INTERNAL_TRACE_EVENT_UID(tracer);     \
+  if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) {   \
+    unsigned int trace_event_flags = flow_flags;                            \
+    v8::internal::tracing::TraceID trace_event_bind_id(bind_id,             \
+                                                       &trace_event_flags); \
+    EventTracer::Handle h = v8::internal::tracing::AddTraceEvent(           \
+        TRACE_EVENT_PHASE_COMPLETE,                                         \
+        INTERNAL_TRACE_EVENT_UID(category_group_enabled), name,             \
+        v8::internal::tracing::kNoId, trace_event_bind_id.data(),           \
+        trace_event_flags, ##__VA_ARGS__);                                  \
+    INTERNAL_TRACE_EVENT_UID(tracer)                                        \
+        .Initialize(INTERNAL_TRACE_EVENT_UID(category_group_enabled), name, \
+                    h);                                                     \
+  }
+
+// Implementation detail: internal macro to create static category and add
+// event if the category is enabled.
+#define INTERNAL_TRACE_EVENT_ADD_WITH_ID(phase, category_group, name, id,      \
+                                         flags, ...)                           \
+  do {                                                                         \
+    INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group);                    \
+    if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) {    \
+      unsigned int trace_event_flags = flags | TRACE_EVENT_FLAG_HAS_ID;        \
+      v8::internal::tracing::TraceID trace_event_trace_id(id,                  \
+                                                          &trace_event_flags); \
+      v8::internal::tracing::AddTraceEvent(                                    \
+          phase, INTERNAL_TRACE_EVENT_UID(category_group_enabled), name,       \
+          trace_event_trace_id.data(), v8::internal::tracing::kNoId,           \
+          trace_event_flags, ##__VA_ARGS__);                                   \
+    }                                                                          \
+  } while (0)
+
+// Adds a trace event with a given timestamp. Not Implemented.
+#define INTERNAL_TRACE_EVENT_ADD_WITH_TIMESTAMP(phase, category_group, name, \
+                                                timestamp, flags, ...)       \
+  UNIMPLEMENTED()
+
+// Adds a trace event with a given id and timestamp. Not Implemented.
+#define INTERNAL_TRACE_EVENT_ADD_WITH_ID_AND_TIMESTAMP(     \
+    phase, category_group, name, id, timestamp, flags, ...) \
+  UNIMPLEMENTED()
+
+// Adds a trace event with a given id, thread_id, and timestamp. Not
+// Implemented.
+#define INTERNAL_TRACE_EVENT_ADD_WITH_ID_TID_AND_TIMESTAMP(            \
+    phase, category_group, name, id, thread_id, timestamp, flags, ...) \
+  UNIMPLEMENTED()
+
+#ifndef INTERNAL_GET_TRACE_CONTEXT_ID
+#define INTERNAL_GET_TRACE_CONTEXT_ID \
+  (uint64_t) v8::internal::Isolate::UnsafeCurrent

[jochen (gone - plz use gerrit), 2015/09/08 14:20:34]

don't use this method.

Isolate* should be always passed around explicitly, you can't rely on getting
the Isolate via any of the *Current() methods

+#endif
+
+namespace v8 {
+namespace internal {
+namespace tracing {
+
+// Specify these values when the corresponding argument of AddTraceEvent is not
+// used.
+const int kZeroNumArgs = 0;
+const uint64_t 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.
+class TraceID {
+ public:
+  class DontMangle {
+   public:
+    explicit DontMangle(const void* id)
+        : data_(static_cast<uint64_t>(reinterpret_cast<uintptr_t>(id))) {}
+    explicit DontMangle(uint64_t id) : data_(id) {}
+    explicit DontMangle(unsigned int id) : data_(id) {}
+    explicit DontMangle(uint16_t id) : data_(id) {}
+    explicit DontMangle(unsigned char id) : data_(id) {}
+    explicit DontMangle(int64_t id) : data_(static_cast<uint64_t>(id)) {}
+    explicit DontMangle(int id) : data_(static_cast<uint64_t>(id)) {}
+    explicit DontMangle(int16_t id) : data_(static_cast<uint64_t>(id)) {}
+    explicit DontMangle(signed char id) : data_(static_cast<uint64_t>(id)) {}
+    uint64_t data() const { return data_; }
+
+   private:
+    uint64_t data_;
+  };
+
+  class ForceMangle {
+   public:
+    explicit ForceMangle(uint64_t id) : data_(id) {}
+    explicit ForceMangle(unsigned int id) : data_(id) {}
+    explicit ForceMangle(uint16_t id) : data_(id) {}
+    explicit ForceMangle(unsigned char id) : data_(id) {}
+    explicit ForceMangle(int64_t id) : data_(static_cast<uint64_t>(id)) {}
+    explicit ForceMangle(int id) : data_(static_cast<uint64_t>(id)) {}
+    explicit ForceMangle(int16_t id) : data_(static_cast<uint64_t>(id)) {}
+    explicit ForceMangle(signed char id) : data_(static_cast<uint64_t>(id)) {}
+    uint64_t data() const { return data_; }
+
+   private:
+    uint64_t data_;
+  };
+
+  TraceID(const void* id, unsigned int* flags)
+      : data_(static_cast<uint64_t>(reinterpret_cast<uintptr_t>(id))) {
+    *flags |= TRACE_EVENT_FLAG_MANGLE_ID;
+  }
+  TraceID(ForceMangle id, unsigned int* flags) : data_(id.data()) {
+    *flags |= TRACE_EVENT_FLAG_MANGLE_ID;
+  }
+  TraceID(DontMangle id, unsigned int* flags) : data_(id.data()) {}
+  TraceID(uint64_t id, unsigned int* flags) : data_(id) { (void)flags; }
+  TraceID(unsigned int id, unsigned int* flags) : data_(id) { (void)flags; }
+  TraceID(uint16_t id, unsigned int* flags) : data_(id) { (void)flags; }
+  TraceID(unsigned char id, unsigned int* flags) : data_(id) { (void)flags; }
+  TraceID(int64_t id, unsigned int* flags) : data_(static_cast<uint64_t>(id)) {
+    (void)flags;
+  }
+  TraceID(int id, unsigned int* flags) : data_(static_cast<uint64_t>(id)) {
+    (void)flags;
+  }
+  TraceID(int16_t id, unsigned int* flags) : data_(static_cast<uint64_t>(id)) {
+    (void)flags;
+  }
+  TraceID(signed char id, unsigned int* flags)
+      : data_(static_cast<uint64_t>(id)) {
+    (void)flags;
+  }
+
+  uint64_t data() const { return data_; }
+
+ private:
+  uint64_t data_;
+};
+
+// Simple union to store various types as uint64_t.
+union TraceValueUnion {
+  bool as_bool;
+  uint64_t as_uint;
+  int64_t as_int;
+  double as_double;
+  const void* as_pointer;
+  const char* as_string;
+};
+
+// Simple container for const char* that should be copied instead of retained.
+class TraceStringWithCopy {
+ public:
+  explicit TraceStringWithCopy(const char* str) : str_(str) {}
+  operator const char*() const { return str_; }
+
+ private:
+  const char* str_;
+};
+
+// Define SetTraceValue for each allowed type. It stores the type and
+// value in the return arguments. This allows this API to avoid declaring any
+// structures so that it is portable to third_party libraries.
+#define INTERNAL_DECLARE_SET_TRACE_VALUE(actual_type, union_member,      \
+                                         value_type_id)                  \
+  static inline void SetTraceValue(actual_type arg, unsigned char* type, \
+                                   uint64_t* value) {                    \
+    TraceValueUnion type_value;                                          \
+    type_value.union_member = arg;                                       \
+    *type = value_type_id;                                               \
+    *value = type_value.as_uint;                                         \
+  }
+// Simpler form for int types that can be safely casted.
+#define INTERNAL_DECLARE_SET_TRACE_VALUE_INT(actual_type, value_type_id) \
+  static inline void SetTraceValue(actual_type arg, unsigned char* type, \
+                                   uint64_t* value) {                    \
+    *type = value_type_id;                                               \
+    *value = static_cast<uint64_t>(arg);                                 \
+  }
+
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(uint64_t, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(unsigned int, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(uint16_t, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(unsigned char, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(int64_t, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(int, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(int16_t, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(signed char, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE(bool, as_bool, TRACE_VALUE_TYPE_BOOL)
+INTERNAL_DECLARE_SET_TRACE_VALUE(double, as_double, TRACE_VALUE_TYPE_DOUBLE)
+INTERNAL_DECLARE_SET_TRACE_VALUE(const void*, as_pointer,
+                                 TRACE_VALUE_TYPE_POINTER)
+INTERNAL_DECLARE_SET_TRACE_VALUE(const char*, as_string,
+                                 TRACE_VALUE_TYPE_STRING)
+INTERNAL_DECLARE_SET_TRACE_VALUE(const TraceStringWithCopy&, as_string,
+                                 TRACE_VALUE_TYPE_COPY_STRING)
+
+#undef INTERNAL_DECLARE_SET_TRACE_VALUE
+#undef INTERNAL_DECLARE_SET_TRACE_VALUE_INT
+
+// These AddTraceEvent template
+// function is defined here instead of in the macro, because the arg_values
+// could be temporary objects, such as std::string. In order to store
+// pointers to the internal c_str and pass through to the tracing API,
+// the arg_values must live throughout these procedures.
+
+static inline EventTracer::Handle AddTraceEvent(
+    char phase, const uint8_t* category_group_enabled, const char* name,
+    uint64_t id, uint64_t bind_id, unsigned int flags) {
+  return TRACE_EVENT_API_ADD_TRACE_EVENT(
+      phase, category_group_enabled, name, id, INTERNAL_GET_TRACE_CONTEXT_ID(),
+      bind_id, kZeroNumArgs, NULL, NULL, NULL,
+      flags | TRACE_EVENT_FLAG_HAS_CONTEXT_ID);
+}
+
+template <class ARG1_TYPE>
+static inline EventTracer::Handle AddTraceEvent(
+    char phase, const uint8_t* category_group_enabled, const char* name,
+    uint64_t id, uint64_t bind_id, unsigned int flags, const char* arg1_name,
+    const ARG1_TYPE& arg1_val) {
+  const int num_args = 1;
+  uint8_t arg_types[1];
+  uint64_t arg_values[1];
+  SetTraceValue(arg1_val, &arg_types[0], &arg_values[0]);
+  return TRACE_EVENT_API_ADD_TRACE_EVENT(
+      phase, category_group_enabled, name, id, INTERNAL_GET_TRACE_CONTEXT_ID(),
+      bind_id, num_args, &arg1_name, arg_types, arg_values,
+      flags | TRACE_EVENT_FLAG_HAS_CONTEXT_ID);
+}
+
+template <class ARG1_TYPE, class ARG2_TYPE>
+static inline EventTracer::Handle AddTraceEvent(
+    char phase, const uint8_t* category_group_enabled, const char* name,
+    uint64_t id, uint64_t bind_id, unsigned int flags, const char* arg1_name,
+    const ARG1_TYPE& arg1_val, const char* arg2_name,
+    const ARG2_TYPE& arg2_val) {
+  const int num_args = 2;
+  const char* arg_names[2] = {arg1_name, arg2_name};
+  unsigned char arg_types[2];
+  uint64_t arg_values[2];
+  SetTraceValue(arg1_val, &arg_types[0], &arg_values[0]);
+  SetTraceValue(arg2_val, &arg_types[1], &arg_values[1]);
+  return TRACE_EVENT_API_ADD_TRACE_EVENT(
+      phase, category_group_enabled, name, id, INTERNAL_GET_TRACE_CONTEXT_ID(),
+      bind_id, num_args, arg_names, arg_types, arg_values,
+      flags | TRACE_EVENT_FLAG_HAS_CONTEXT_ID);
+}
+
+// Used by TRACE_EVENTx macros. Do not use directly.
+class ScopedTracer {
+ public:
+  // Note: members of data_ intentionally left uninitialized. See Initialize.
+  ScopedTracer() : p_data_(NULL) {}
+
+  ~ScopedTracer() {
+    if (p_data_ && *data_.category_group_enabled)
+      TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(
+          data_.category_group_enabled, data_.name, data_.event_handle);
+  }
+
+  void Initialize(const uint8_t* category_group_enabled, const char* name,
+                  EventTracer::Handle event_handle) {
+    data_.category_group_enabled = category_group_enabled;
+    data_.name = name;
+    data_.event_handle = event_handle;
+    p_data_ = &data_;
+  }
+
+ private:
+  // This Data struct workaround is to avoid initializing all the members
+  // in Data during construction of this object, since this object is always
+  // constructed, even when tracing is disabled. If the members of Data were
+  // members of this class instead, compiler warnings occur about potential
+  // uninitialized accesses.
+  struct Data {
+    const uint8_t* category_group_enabled;
+    const char* name;
+    EventTracer::Handle event_handle;
+  };
+  Data* p_data_;
+  Data data_;
+};
+
+// Used by TRACE_EVENT_BINARY_EFFICIENTx macro. Do not use directly.
+class ScopedTraceBinaryEfficient {
+ public:
+  ScopedTraceBinaryEfficient(const char* category_group, const char* name);
+  ~ScopedTraceBinaryEfficient();
+
+ private:
+  const uint8_t* category_group_enabled_;
+  const char* name_;
+  EventTracer::Handle event_handle_;
+};
+
+// TraceEventSamplingStateScope records the current sampling state
+// and sets a new sampling state. When the scope exists, it restores
+// the sampling state having recorded.
+template <size_t BucketNumber>
+class TraceEventSamplingStateScope {
+ public:
+  explicit TraceEventSamplingStateScope(const char* category_and_name) {
+    previous_state_ = TraceEventSamplingStateScope<BucketNumber>::Current();
+    TraceEventSamplingStateScope<BucketNumber>::Set(category_and_name);
+  }
+
+  ~TraceEventSamplingStateScope() {
+    TraceEventSamplingStateScope<BucketNumber>::Set(previous_state_);
+  }
+
+  static inline const char* Current() {
+    return reinterpret_cast<const char*>(
+        TRACE_EVENT_API_ATOMIC_LOAD(g_trace_state[BucketNumber]));
+  }
+
+  static inline void Set(const char* category_and_name) {
+    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_;
+};
+
+}  // namespace tracing
+}  // namespace internal
+}  // namespace v8
+
+#endif  // SRC_TRACING_TRACE_EVENT_H_