1// Copyright 2016 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef BASE_TRACE_EVENT_TRACE_CATEGORY_H_
6#define BASE_TRACE_EVENT_TRACE_CATEGORY_H_
7
8#include <stdint.h>
9
10namespace base {
11namespace trace_event {
12
13// Captures the state of an invidivual trace category. Nothing except tracing
14// internals (e.g., TraceLog) is supposed to have non-const Category pointers.
15struct TraceCategory {
16  // The TRACE_EVENT macros should only use this value as a bool.
17  // These enum values are effectively a public API and third_party projects
18  // depend on their value. Hence, never remove or recycle existing bits, unless
19  // you are sure that all the third-party projects that depend on this have
20  // been updated.
21  enum StateFlags : uint8_t {
22    ENABLED_FOR_RECORDING = 1 << 0,
23
24    // Not used anymore.
25    DEPRECATED_ENABLED_FOR_MONITORING = 1 << 1,
26    DEPRECATED_ENABLED_FOR_EVENT_CALLBACK = 1 << 2,
27
28    ENABLED_FOR_ETW_EXPORT = 1 << 3,
29    ENABLED_FOR_FILTERING = 1 << 4
30  };
31
32  static const TraceCategory* FromStatePtr(const uint8_t* state_ptr) {
33    static_assert(
34        offsetof(TraceCategory, state_) == 0,
35        "|state_| must be the first field of the TraceCategory class.");
36    return reinterpret_cast<const TraceCategory*>(state_ptr);
37  }
38
39  bool is_valid() const { return name_ != nullptr; }
40  void set_name(const char* name) { name_ = name; }
41  const char* name() const {
42    DCHECK(is_valid());
43    return name_;
44  }
45
46  // TODO(primiano): This is an intermediate solution to deal with the fact that
47  // today TRACE_EVENT* macros cache the state ptr. They should just cache the
48  // full TraceCategory ptr, which is immutable, and use these helper function
49  // here. This will get rid of the need of this awkward ptr getter completely.
50  const uint8_t* state_ptr() const {
51    return const_cast<const uint8_t*>(&state_);
52  }
53
54  uint8_t state() const {
55    return *const_cast<volatile const uint8_t*>(&state_);
56  }
57
58  bool is_enabled() const { return state() != 0; }
59
60  void set_state(uint8_t state) {
61    *const_cast<volatile uint8_t*>(&state_) = state;
62  }
63
64  void clear_state_flag(StateFlags flag) { set_state(state() & (~flag)); }
65  void set_state_flag(StateFlags flag) { set_state(state() | flag); }
66
67  uint32_t enabled_filters() const {
68    return *const_cast<volatile const uint32_t*>(&enabled_filters_);
69  }
70
71  bool is_filter_enabled(size_t index) const {
72    DCHECK(index < sizeof(enabled_filters_) * 8);
73    return (enabled_filters() & (1 << index)) != 0;
74  }
75
76  void set_enabled_filters(uint32_t enabled_filters) {
77    *const_cast<volatile uint32_t*>(&enabled_filters_) = enabled_filters;
78  }
79
80  void reset_for_testing() {
81    set_state(0);
82    set_enabled_filters(0);
83  }
84
85  // These fields should not be accessed directly, not even by tracing code.
86  // The only reason why these are not private is because it makes it impossible
87  // to have a global array of TraceCategory in category_registry.cc without
88  // creating initializers. See discussion on goo.gl/qhZN94 and
89  // crbug.com/{660967,660828}.
90
91  // The enabled state. TRACE_EVENT* macros will capture events if any of the
92  // flags here are set. Since TRACE_EVENTx macros are used in a lot of
93  // fast-paths, accesses to this field are non-barriered and racy by design.
94  // This field is mutated when starting/stopping tracing and we don't care
95  // about missing some events.
96  uint8_t state_;
97
98  // When ENABLED_FOR_FILTERING is set, this contains a bitmap to the
99  // coressponding filter (see event_filters.h).
100  uint32_t enabled_filters_;
101
102  // TraceCategory group names are long lived static strings.
103  const char* name_;
104};
105
106}  // namespace trace_event
107}  // namespace base
108
109#endif  // BASE_TRACE_EVENT_TRACE_CATEGORY_H_
110