summaryrefslogtreecommitdiff
path: root/absl/flags/reflection.cc
blob: 1b0258350f718552b56214dfb2d6e36e084fe7aa (plain)
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
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
//
//  Copyright 2020 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.

#include "absl/flags/reflection.h"

#include <assert.h>

#include <map>
#include <string>

#include "absl/base/config.h"
#include "absl/base/thread_annotations.h"
#include "absl/flags/commandlineflag.h"
#include "absl/flags/internal/private_handle_accessor.h"
#include "absl/flags/internal/registry.h"
#include "absl/flags/usage_config.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/string_view.h"
#include "absl/synchronization/mutex.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace flags_internal {

// --------------------------------------------------------------------
// FlagRegistry
//    A FlagRegistry singleton object holds all flag objects indexed by their
//    names so that if you know a flag's name, you can access or set it. If the
//    function is named FooLocked(), you must own the registry lock before
//    calling the function; otherwise, you should *not* hold the lock, and the
//    function will acquire it itself if needed.
// --------------------------------------------------------------------

class FlagRegistry {
 public:
  FlagRegistry() = default;
  ~FlagRegistry() = default;

  // Store a flag in this registry. Takes ownership of *flag.
  void RegisterFlag(CommandLineFlag& flag);

  void Lock() ABSL_EXCLUSIVE_LOCK_FUNCTION(lock_) { lock_.Lock(); }
  void Unlock() ABSL_UNLOCK_FUNCTION(lock_) { lock_.Unlock(); }

  // Returns the flag object for the specified name, or nullptr if not found.
  // Will emit a warning if a 'retired' flag is specified.
  CommandLineFlag* FindFlagLocked(absl::string_view name);

  static FlagRegistry& GlobalRegistry();  // returns a singleton registry

 private:
  friend class flags_internal::FlagSaverImpl;  // reads all the flags in order
                                               // to copy them
  friend void ForEachFlagUnlocked(
      std::function<void(CommandLineFlag&)> visitor);

  // The map from name to flag, for FindFlagLocked().
  using FlagMap = std::map<absl::string_view, CommandLineFlag*>;
  using FlagIterator = FlagMap::iterator;
  using FlagConstIterator = FlagMap::const_iterator;
  FlagMap flags_;

  absl::Mutex lock_;

  // Disallow
  FlagRegistry(const FlagRegistry&);
  FlagRegistry& operator=(const FlagRegistry&);
};

CommandLineFlag* FlagRegistry::FindFlagLocked(absl::string_view name) {
  FlagConstIterator i = flags_.find(name);
  if (i == flags_.end()) {
    return nullptr;
  }

  return i->second;
}

namespace {

class FlagRegistryLock {
 public:
  explicit FlagRegistryLock(FlagRegistry& fr) : fr_(fr) { fr_.Lock(); }
  ~FlagRegistryLock() { fr_.Unlock(); }

 private:
  FlagRegistry& fr_;
};

void DestroyRetiredFlag(CommandLineFlag& flag);

}  // namespace

void FlagRegistry::RegisterFlag(CommandLineFlag& flag) {
  FlagRegistryLock registry_lock(*this);
  std::pair<FlagIterator, bool> ins =
      flags_.insert(FlagMap::value_type(flag.Name(), &flag));
  if (ins.second == false) {  // means the name was already in the map
    CommandLineFlag& old_flag = *ins.first->second;
    if (flag.IsRetired() != old_flag.IsRetired()) {
      // All registrations must agree on the 'retired' flag.
      flags_internal::ReportUsageError(
          absl::StrCat(
              "Retired flag '", flag.Name(), "' was defined normally in file '",
              (flag.IsRetired() ? old_flag.Filename() : flag.Filename()), "'."),
          true);
    } else if (flags_internal::PrivateHandleAccessor::TypeId(flag) !=
               flags_internal::PrivateHandleAccessor::TypeId(old_flag)) {
      flags_internal::ReportUsageError(
          absl::StrCat("Flag '", flag.Name(),
                       "' was defined more than once but with "
                       "differing types. Defined in files '",
                       old_flag.Filename(), "' and '", flag.Filename(), "'."),
          true);
    } else if (old_flag.IsRetired()) {
      // Retired flag can just be deleted.
      DestroyRetiredFlag(flag);
      return;
    } else if (old_flag.Filename() != flag.Filename()) {
      flags_internal::ReportUsageError(
          absl::StrCat("Flag '", flag.Name(),
                       "' was defined more than once (in files '",
                       old_flag.Filename(), "' and '", flag.Filename(), "')."),
          true);
    } else {
      flags_internal::ReportUsageError(
          absl::StrCat(
              "Something is wrong with flag '", flag.Name(), "' in file '",
              flag.Filename(), "'. One possibility: file '", flag.Filename(),
              "' is being linked both statically and dynamically into this "
              "executable. e.g. some files listed as srcs to a test and also "
              "listed as srcs of some shared lib deps of the same test."),
          true);
    }
    // All cases above are fatal, except for the retired flags.
    std::exit(1);
  }
}

FlagRegistry& FlagRegistry::GlobalRegistry() {
  static FlagRegistry* global_registry = new FlagRegistry;
  return *global_registry;
}

// --------------------------------------------------------------------

void ForEachFlagUnlocked(std::function<void(CommandLineFlag&)> visitor) {
  FlagRegistry& registry = FlagRegistry::GlobalRegistry();
  for (FlagRegistry::FlagConstIterator i = registry.flags_.begin();
       i != registry.flags_.end(); ++i) {
    visitor(*i->second);
  }
}

void ForEachFlag(std::function<void(CommandLineFlag&)> visitor) {
  FlagRegistry& registry = FlagRegistry::GlobalRegistry();
  FlagRegistryLock frl(registry);
  ForEachFlagUnlocked(visitor);
}

// --------------------------------------------------------------------

bool RegisterCommandLineFlag(CommandLineFlag& flag) {
  FlagRegistry::GlobalRegistry().RegisterFlag(flag);
  return true;
}

// --------------------------------------------------------------------

namespace {

class RetiredFlagObj final : public CommandLineFlag {
 public:
  constexpr RetiredFlagObj(const char* name, FlagFastTypeId type_id)
      : name_(name), type_id_(type_id) {}

 private:
  absl::string_view Name() const override { return name_; }
  std::string Filename() const override {
    OnAccess();
    return "RETIRED";
  }
  FlagFastTypeId TypeId() const override { return type_id_; }
  std::string Help() const override {
    OnAccess();
    return "";
  }
  bool IsRetired() const override { return true; }
  bool IsSpecifiedOnCommandLine() const override {
    OnAccess();
    return false;
  }
  std::string DefaultValue() const override {
    OnAccess();
    return "";
  }
  std::string CurrentValue() const override {
    OnAccess();
    return "";
  }

  // Any input is valid
  bool ValidateInputValue(absl::string_view) const override {
    OnAccess();
    return true;
  }

  std::unique_ptr<flags_internal::FlagStateInterface> SaveState() override {
    return nullptr;
  }

  bool ParseFrom(absl::string_view, flags_internal::FlagSettingMode,
                 flags_internal::ValueSource, std::string&) override {
    OnAccess();
    return false;
  }

  void CheckDefaultValueParsingRoundtrip() const override { OnAccess(); }

  void Read(void*) const override { OnAccess(); }

  void OnAccess() const {
    flags_internal::ReportUsageError(
        absl::StrCat("Accessing retired flag '", name_, "'"), false);
  }

  // Data members
  const char* const name_;
  const FlagFastTypeId type_id_;
};

void DestroyRetiredFlag(CommandLineFlag& flag) {
  assert(flag.IsRetired());
  delete static_cast<RetiredFlagObj*>(&flag);
}

}  // namespace

bool Retire(const char* name, FlagFastTypeId type_id) {
  auto* flag = new flags_internal::RetiredFlagObj(name, type_id);
  FlagRegistry::GlobalRegistry().RegisterFlag(*flag);
  return true;
}

// --------------------------------------------------------------------

class FlagSaverImpl {
 public:
  FlagSaverImpl() = default;
  FlagSaverImpl(const FlagSaverImpl&) = delete;
  void operator=(const FlagSaverImpl&) = delete;

  // Saves the flag states from the flag registry into this object.
  // It's an error to call this more than once.
  void SaveFromRegistry() {
    assert(backup_registry_.empty());  // call only once!
    flags_internal::ForEachFlag([&](CommandLineFlag& flag) {
      if (auto flag_state =
              flags_internal::PrivateHandleAccessor::SaveState(flag)) {
        backup_registry_.emplace_back(std::move(flag_state));
      }
    });
  }

  // Restores the saved flag states into the flag registry.
  void RestoreToRegistry() {
    for (const auto& flag_state : backup_registry_) {
      flag_state->Restore();
    }
  }

 private:
  std::vector<std::unique_ptr<flags_internal::FlagStateInterface>>
      backup_registry_;
};

}  // namespace flags_internal

FlagSaver::FlagSaver() : impl_(new flags_internal::FlagSaverImpl) {
  impl_->SaveFromRegistry();
}

FlagSaver::~FlagSaver() {
  if (!impl_) return;

  impl_->RestoreToRegistry();
  delete impl_;
}

// --------------------------------------------------------------------

CommandLineFlag* FindCommandLineFlag(absl::string_view name) {
  if (name.empty()) return nullptr;
  flags_internal::FlagRegistry& registry =
      flags_internal::FlagRegistry::GlobalRegistry();
  flags_internal::FlagRegistryLock frl(registry);

  return registry.FindFlagLocked(name);
}

ABSL_NAMESPACE_END
}  // namespace absl