about summary refs log tree commit diff
path: root/absl/flags/internal/flag.cc
blob: a944e16e50832d0dd7d9c2777c6d611730f2b9c6 (plain) (blame)
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
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
//
// Copyright 2019 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/internal/flag.h"

#include <stddef.h>
#include <stdint.h>
#include <string.h>

#include <atomic>
#include <memory>
#include <string>
#include <vector>

#include "absl/base/attributes.h"
#include "absl/base/config.h"
#include "absl/base/const_init.h"
#include "absl/base/optimization.h"
#include "absl/flags/internal/commandlineflag.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 {

// The help message indicating that the commandline flag has been
// 'stripped'. It will not show up when doing "-help" and its
// variants. The flag is stripped if ABSL_FLAGS_STRIP_HELP is set to 1
// before including absl/flags/flag.h
const char kStrippedFlagHelp[] = "\001\002\003\004 (unknown) \004\003\002\001";

namespace {

// Currently we only validate flag values for user-defined flag types.
bool ShouldValidateFlagValue(FlagStaticTypeId flag_type_id) {
#define DONT_VALIDATE(T) \
  if (flag_type_id == &FlagStaticTypeIdGen<T>) return false;
  ABSL_FLAGS_INTERNAL_BUILTIN_TYPES(DONT_VALIDATE)
#undef DONT_VALIDATE

  return true;
}

// RAII helper used to temporarily unlock and relock `absl::Mutex`.
// This is used when we need to ensure that locks are released while
// invoking user supplied callbacks and then reacquired, since callbacks may
// need to acquire these locks themselves.
class MutexRelock {
 public:
  explicit MutexRelock(absl::Mutex* mu) : mu_(mu) { mu_->Unlock(); }
  ~MutexRelock() { mu_->Lock(); }

  MutexRelock(const MutexRelock&) = delete;
  MutexRelock& operator=(const MutexRelock&) = delete;

 private:
  absl::Mutex* mu_;
};

}  // namespace

void FlagImpl::Init() {
  new (&data_guard_) absl::Mutex;

  // At this point the default_value_ always points to gen_func.
  std::unique_ptr<void, DynValueDeleter> init_value(
      (*default_value_.gen_func)(), DynValueDeleter{op_});
  switch (ValueStorageKind()) {
    case FlagValueStorageKind::kHeapAllocated:
      value_.dynamic = init_value.release();
      break;
    case FlagValueStorageKind::kOneWordAtomic: {
      int64_t atomic_value;
      std::memcpy(&atomic_value, init_value.get(), Sizeof(op_));
      value_.one_word_atomic.store(atomic_value, std::memory_order_release);
      break;
    }
    case FlagValueStorageKind::kTwoWordsAtomic: {
      AlignedTwoWords atomic_value{0, 0};
      std::memcpy(&atomic_value, init_value.get(), Sizeof(op_));
      value_.two_words_atomic.store(atomic_value, std::memory_order_release);
      break;
    }
  }
}

absl::Mutex* FlagImpl::DataGuard() const {
  absl::call_once(const_cast<FlagImpl*>(this)->init_control_, &FlagImpl::Init,
                  const_cast<FlagImpl*>(this));

  // data_guard_ is initialized inside Init.
  return reinterpret_cast<absl::Mutex*>(&data_guard_);
}

void FlagImpl::AssertValidType(FlagStaticTypeId type_id) const {
  FlagStaticTypeId this_type_id = flags_internal::StaticTypeId(op_);

  // `type_id` is the type id corresponding to the declaration visibile at the
  // call site. `this_type_id` is the type id corresponding to the type stored
  // during flag definition. They must match for this operation to be
  // well-defined.
  if (ABSL_PREDICT_TRUE(type_id == this_type_id)) return;

  void* lhs_runtime_type_id = type_id();
  void* rhs_runtime_type_id = this_type_id();

  if (lhs_runtime_type_id == rhs_runtime_type_id) return;

#if defined(ABSL_FLAGS_INTERNAL_HAS_RTTI)
  if (*reinterpret_cast<std::type_info*>(lhs_runtime_type_id) ==
      *reinterpret_cast<std::type_info*>(rhs_runtime_type_id))
    return;
#endif

  ABSL_INTERNAL_LOG(
      FATAL, absl::StrCat("Flag '", Name(),
                          "' is defined as one type and declared as another"));
}

std::unique_ptr<void, DynValueDeleter> FlagImpl::MakeInitValue() const {
  void* res = nullptr;
  if (DefaultKind() == FlagDefaultKind::kDynamicValue) {
    res = flags_internal::Clone(op_, default_value_.dynamic_value);
  } else {
    res = (*default_value_.gen_func)();
  }
  return {res, DynValueDeleter{op_}};
}

void FlagImpl::StoreValue(const void* src) {
  switch (ValueStorageKind()) {
    case FlagValueStorageKind::kHeapAllocated:
      Copy(op_, src, value_.dynamic);
      break;
    case FlagValueStorageKind::kOneWordAtomic: {
      int64_t one_word_val;
      std::memcpy(&one_word_val, src, Sizeof(op_));
      value_.one_word_atomic.store(one_word_val, std::memory_order_release);
      break;
    }
    case FlagValueStorageKind::kTwoWordsAtomic: {
      AlignedTwoWords two_words_val{0, 0};
      std::memcpy(&two_words_val, src, Sizeof(op_));
      value_.two_words_atomic.store(two_words_val, std::memory_order_release);
      break;
    }
  }

  modified_ = true;
  ++counter_;
  InvokeCallback();
}

absl::string_view FlagImpl::Name() const { return name_; }

std::string FlagImpl::Filename() const {
  return flags_internal::GetUsageConfig().normalize_filename(filename_);
}

std::string FlagImpl::Help() const {
  return HelpSourceKind() == FlagHelpKind::kLiteral ? help_.literal
                                                    : help_.gen_func();
}

bool FlagImpl::IsModified() const {
  absl::MutexLock l(DataGuard());
  return modified_;
}

bool FlagImpl::IsSpecifiedOnCommandLine() const {
  absl::MutexLock l(DataGuard());
  return on_command_line_;
}

std::string FlagImpl::DefaultValue() const {
  absl::MutexLock l(DataGuard());

  auto obj = MakeInitValue();
  return flags_internal::Unparse(op_, obj.get());
}

std::string FlagImpl::CurrentValue() const {
  DataGuard();  // Make sure flag initialized
  switch (ValueStorageKind()) {
    case FlagValueStorageKind::kHeapAllocated: {
      absl::MutexLock l(DataGuard());
      return flags_internal::Unparse(op_, value_.dynamic);
    }
    case FlagValueStorageKind::kOneWordAtomic: {
      const auto one_word_val =
          value_.one_word_atomic.load(std::memory_order_acquire);
      return flags_internal::Unparse(op_, &one_word_val);
    }
    case FlagValueStorageKind::kTwoWordsAtomic: {
      const auto two_words_val =
          value_.two_words_atomic.load(std::memory_order_acquire);
      return flags_internal::Unparse(op_, &two_words_val);
    }
  }

  return "";
}

void FlagImpl::SetCallback(const FlagCallbackFunc mutation_callback) {
  absl::MutexLock l(DataGuard());

  if (callback_ == nullptr) {
    callback_ = new FlagCallback;
  }
  callback_->func = mutation_callback;

  InvokeCallback();
}

void FlagImpl::InvokeCallback() const {
  if (!callback_) return;

  // Make a copy of the C-style function pointer that we are about to invoke
  // before we release the lock guarding it.
  FlagCallbackFunc cb = callback_->func;

  // If the flag has a mutation callback this function invokes it. While the
  // callback is being invoked the primary flag's mutex is unlocked and it is
  // re-locked back after call to callback is completed. Callback invocation is
  // guarded by flag's secondary mutex instead which prevents concurrent
  // callback invocation. Note that it is possible for other thread to grab the
  // primary lock and update flag's value at any time during the callback
  // invocation. This is by design. Callback can get a value of the flag if
  // necessary, but it might be different from the value initiated the callback
  // and it also can be different by the time the callback invocation is
  // completed. Requires that *primary_lock be held in exclusive mode; it may be
  // released and reacquired by the implementation.
  MutexRelock relock(DataGuard());
  absl::MutexLock lock(&callback_->guard);
  cb();
}

bool FlagImpl::RestoreState(const void* value, bool modified,
                            bool on_command_line, int64_t counter) {
  {
    absl::MutexLock l(DataGuard());

    if (counter_ == counter) return false;
  }

  Write(value);

  {
    absl::MutexLock l(DataGuard());

    modified_ = modified;
    on_command_line_ = on_command_line;
  }

  return true;
}

// Attempts to parse supplied `value` string using parsing routine in the `flag`
// argument. If parsing successful, this function replaces the dst with newly
// parsed value. In case if any error is encountered in either step, the error
// message is stored in 'err'
std::unique_ptr<void, DynValueDeleter> FlagImpl::TryParse(
    absl::string_view value, std::string* err) const {
  std::unique_ptr<void, DynValueDeleter> tentative_value = MakeInitValue();

  std::string parse_err;
  if (!flags_internal::Parse(op_, value, tentative_value.get(), &parse_err)) {
    absl::string_view err_sep = parse_err.empty() ? "" : "; ";
    *err = absl::StrCat("Illegal value '", value, "' specified for flag '",
                        Name(), "'", err_sep, parse_err);
    return nullptr;
  }

  return tentative_value;
}

void FlagImpl::Read(void* dst) const {
  DataGuard();  // Make sure flag initialized
  switch (ValueStorageKind()) {
    case FlagValueStorageKind::kHeapAllocated: {
      absl::MutexLock l(DataGuard());

      flags_internal::CopyConstruct(op_, value_.dynamic, dst);
      break;
    }
    case FlagValueStorageKind::kOneWordAtomic: {
      const auto one_word_val =
          value_.one_word_atomic.load(std::memory_order_acquire);
      std::memcpy(dst, &one_word_val, Sizeof(op_));
      break;
    }
    case FlagValueStorageKind::kTwoWordsAtomic: {
      const auto two_words_val =
          value_.two_words_atomic.load(std::memory_order_acquire);
      std::memcpy(dst, &two_words_val, Sizeof(op_));
      break;
    }
  }
}

void FlagImpl::Write(const void* src) {
  absl::MutexLock l(DataGuard());

  if (ShouldValidateFlagValue(flags_internal::StaticTypeId(op_))) {
    std::unique_ptr<void, DynValueDeleter> obj{flags_internal::Clone(op_, src),
                                               DynValueDeleter{op_}};
    std::string ignored_error;
    std::string src_as_str = flags_internal::Unparse(op_, src);
    if (!flags_internal::Parse(op_, src_as_str, obj.get(), &ignored_error)) {
      ABSL_INTERNAL_LOG(ERROR, absl::StrCat("Attempt to set flag '", Name(),
                                            "' to invalid value ", src_as_str));
    }
  }

  StoreValue(src);
}

// Sets the value of the flag based on specified string `value`. If the flag
// was successfully set to new value, it returns true. Otherwise, sets `err`
// to indicate the error, leaves the flag unchanged, and returns false. There
// are three ways to set the flag's value:
//  * Update the current flag value
//  * Update the flag's default value
//  * Update the current flag value if it was never set before
// The mode is selected based on 'set_mode' parameter.
bool FlagImpl::SetFromString(absl::string_view value, FlagSettingMode set_mode,
                             ValueSource source, std::string* err) {
  absl::MutexLock l(DataGuard());

  switch (set_mode) {
    case SET_FLAGS_VALUE: {
      // set or modify the flag's value
      auto tentative_value = TryParse(value, err);
      if (!tentative_value) return false;

      StoreValue(tentative_value.get());

      if (source == kCommandLine) {
        on_command_line_ = true;
      }
      break;
    }
    case SET_FLAG_IF_DEFAULT: {
      // set the flag's value, but only if it hasn't been set by someone else
      if (modified_) {
        // TODO(rogeeff): review and fix this semantic. Currently we do not fail
        // in this case if flag is modified. This is misleading since the flag's
        // value is not updated even though we return true.
        // *err = absl::StrCat(Name(), " is already set to ",
        //                     CurrentValue(), "\n");
        // return false;
        return true;
      }
      auto tentative_value = TryParse(value, err);
      if (!tentative_value) return false;

      StoreValue(tentative_value.get());
      break;
    }
    case SET_FLAGS_DEFAULT: {
      auto tentative_value = TryParse(value, err);
      if (!tentative_value) return false;

      if (DefaultKind() == FlagDefaultKind::kDynamicValue) {
        void* old_value = default_value_.dynamic_value;
        default_value_.dynamic_value = tentative_value.release();
        tentative_value.reset(old_value);
      } else {
        default_value_.dynamic_value = tentative_value.release();
        def_kind_ = static_cast<uint8_t>(FlagDefaultKind::kDynamicValue);
      }

      if (!modified_) {
        // Need to set both default value *and* current, in this case.
        StoreValue(default_value_.dynamic_value);
        modified_ = false;
      }
      break;
    }
  }

  return true;
}

void FlagImpl::CheckDefaultValueParsingRoundtrip() const {
  std::string v = DefaultValue();

  absl::MutexLock lock(DataGuard());

  auto dst = MakeInitValue();
  std::string error;
  if (!flags_internal::Parse(op_, v, dst.get(), &error)) {
    ABSL_INTERNAL_LOG(
        FATAL,
        absl::StrCat("Flag ", Name(), " (from ", Filename(),
                     "): std::string form of default value '", v,
                     "' could not be parsed; error=", error));
  }

  // We do not compare dst to def since parsing/unparsing may make
  // small changes, e.g., precision loss for floating point types.
}

bool FlagImpl::ValidateInputValue(absl::string_view value) const {
  absl::MutexLock l(DataGuard());

  auto obj = MakeInitValue();
  std::string ignored_error;
  return flags_internal::Parse(op_, value, obj.get(), &ignored_error);
}

}  // namespace flags_internal
ABSL_NAMESPACE_END
}  // namespace absl