1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
|
// Copyright 2022 The Abseil Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// -----------------------------------------------------------------------------
// vlog_config.h
// -----------------------------------------------------------------------------
//
// This header file defines `VLogSite`, a public primitive that represents
// a callsite for the `VLOG` family of macros and related libraries.
// It also declares and defines multiple internal utilities used to implement
// `VLOG`, such as `VLogSiteManager`.
#ifndef ABSL_LOG_INTERNAL_VLOG_CONFIG_H_
#define ABSL_LOG_INTERNAL_VLOG_CONFIG_H_
// IWYU pragma: private, include "absl/log/log.h"
#include <atomic>
#include <cstdint>
#include <functional>
#include <limits>
#include <type_traits>
#include "absl/base/attributes.h"
#include "absl/base/config.h"
#include "absl/base/optimization.h"
#include "absl/base/thread_annotations.h"
#include "absl/strings/string_view.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace log_internal {
class SyntheticBinary;
class VLogSite;
int RegisterAndInitialize(VLogSite* v);
void UpdateVLogSites();
constexpr int kUseFlag = (std::numeric_limits<int16_t>::min)();
// Represents a unique callsite for a `VLOG()` or `VLOG_IS_ON()` call.
//
// Libraries that provide `VLOG`-like functionality should use this to
// efficiently handle --vmodule.
//
// VLogSite objects must not be destroyed until the program exits. Doing so will
// probably yield nasty segfaults in VLogSiteManager::UpdateLogSites(). The
// recommendation is to make all such objects function-local statics.
class VLogSite final {
public:
// `f` must not be destroyed until the program exits.
explicit constexpr VLogSite(const char* f)
: file_(f), v_(kUninitialized), next_(nullptr) {}
VLogSite(const VLogSite&) = delete;
VLogSite& operator=(const VLogSite&) = delete;
// Inlining the function yields a ~3x performance improvement at the cost of a
// 1.5x code size increase at the call site.
// Takes locks but does not allocate memory.
ABSL_ATTRIBUTE_ALWAYS_INLINE
bool IsEnabled(int level) {
int stale_v = v_.load(std::memory_order_relaxed);
if (ABSL_PREDICT_TRUE(level > stale_v)) {
return false;
}
// We put everything other than the fast path, i.e. vlogging is initialized
// but not on, behind an out-of-line function to reduce code size.
// "level" is almost always a call-site constant, so we can save a bit
// of code space by special-casing for a few common levels.
#if ABSL_HAVE_BUILTIN(__builtin_constant_p) || defined(__GNUC__)
if (__builtin_constant_p(level)) {
if (level == 0) return SlowIsEnabled0(stale_v);
if (level == 1) return SlowIsEnabled1(stale_v);
if (level == 2) return SlowIsEnabled2(stale_v);
if (level == 3) return SlowIsEnabled3(stale_v);
if (level == 4) return SlowIsEnabled4(stale_v);
if (level == 5) return SlowIsEnabled5(stale_v);
}
#endif
return SlowIsEnabled(stale_v, level);
}
private:
friend int log_internal::RegisterAndInitialize(VLogSite* v);
friend void log_internal::UpdateVLogSites();
friend class log_internal::SyntheticBinary;
static constexpr int kUninitialized = (std::numeric_limits<int>::max)();
// SlowIsEnabled performs slower checks to determine whether a log site is
// enabled. Because it is expected to be called somewhat rarely
// (comparatively), it is not inlined to save on code size.
//
// Prerequisites to calling SlowIsEnabled:
// 1) stale_v is uninitialized OR
// 2) stale_v is initialized and >= level (meaning we must log).
// Takes locks but does not allocate memory.
ABSL_ATTRIBUTE_NOINLINE
bool SlowIsEnabled(int stale_v, int level);
ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled0(int stale_v);
ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled1(int stale_v);
ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled2(int stale_v);
ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled3(int stale_v);
ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled4(int stale_v);
ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled5(int stale_v);
// This object is too size-sensitive to use absl::string_view.
const char* const file_;
std::atomic<int> v_;
std::atomic<VLogSite*> next_;
};
static_assert(std::is_trivially_destructible<VLogSite>::value,
"VLogSite must be trivially destructible");
// Returns the current verbose log level of `file`.
// Does not allocate memory.
int VLogLevel(absl::string_view file);
// Registers a site `v` to get updated as `vmodule` and `v` change. Also
// initializes the site based on their current values, and returns that result.
// Does not allocate memory.
int RegisterAndInitialize(VLogSite* v);
// Allocates memory.
void UpdateVLogSites();
// Completely overwrites the saved value of `vmodule`.
// Allocates memory.
void UpdateVModule(absl::string_view vmodule);
// Updates the global verbosity level to `v` and returns the prior value.
// Allocates memory.
int UpdateGlobalVLogLevel(int v);
// Atomically prepends `module_pattern=log_level` to the start of vmodule.
// Returns the prior value for `module_pattern` if there was an exact match and
// `global_v` otherwise.
// Allocates memory.
int PrependVModule(absl::string_view module_pattern, int log_level);
// Registers `on_update` to be called whenever `v` or `vmodule` change.
// Allocates memory.
void OnVLogVerbosityUpdate(std::function<void()> cb);
// Does not allocate memory.
VLogSite* SetVModuleListHeadForTestOnly(VLogSite* v);
} // namespace log_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_LOG_INTERNAL_VLOG_CONFIG_H_
|
