about summary refs log tree commit diff
path: root/absl/container/internal/container_memory.h
blob: d24b0f8413845312201aeb5ecc56dba329566002 (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
430
431
432
433
434
435
436
437
438
439
440
// Copyright 2018 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.

#ifndef ABSL_CONTAINER_INTERNAL_CONTAINER_MEMORY_H_
#define ABSL_CONTAINER_INTERNAL_CONTAINER_MEMORY_H_

#ifdef ADDRESS_SANITIZER
#include <sanitizer/asan_interface.h>
#endif

#ifdef MEMORY_SANITIZER
#include <sanitizer/msan_interface.h>
#endif

#include <cassert>
#include <cstddef>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>

#include "absl/memory/memory.h"
#include "absl/utility/utility.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace container_internal {

// Allocates at least n bytes aligned to the specified alignment.
// Alignment must be a power of 2. It must be positive.
//
// Note that many allocators don't honor alignment requirements above certain
// threshold (usually either alignof(std::max_align_t) or alignof(void*)).
// Allocate() doesn't apply alignment corrections. If the underlying allocator
// returns insufficiently alignment pointer, that's what you are going to get.
template <size_t Alignment, class Alloc>
void* Allocate(Alloc* alloc, size_t n) {
  static_assert(Alignment > 0, "");
  assert(n && "n must be positive");
  struct alignas(Alignment) M {};
  using A = typename absl::allocator_traits<Alloc>::template rebind_alloc<M>;
  using AT = typename absl::allocator_traits<Alloc>::template rebind_traits<M>;
  A mem_alloc(*alloc);
  void* p = AT::allocate(mem_alloc, (n + sizeof(M) - 1) / sizeof(M));
  assert(reinterpret_cast<uintptr_t>(p) % Alignment == 0 &&
         "allocator does not respect alignment");
  return p;
}

// The pointer must have been previously obtained by calling
// Allocate<Alignment>(alloc, n).
template <size_t Alignment, class Alloc>
void Deallocate(Alloc* alloc, void* p, size_t n) {
  static_assert(Alignment > 0, "");
  assert(n && "n must be positive");
  struct alignas(Alignment) M {};
  using A = typename absl::allocator_traits<Alloc>::template rebind_alloc<M>;
  using AT = typename absl::allocator_traits<Alloc>::template rebind_traits<M>;
  A mem_alloc(*alloc);
  AT::deallocate(mem_alloc, static_cast<M*>(p),
                 (n + sizeof(M) - 1) / sizeof(M));
}

namespace memory_internal {

// Constructs T into uninitialized storage pointed by `ptr` using the args
// specified in the tuple.
template <class Alloc, class T, class Tuple, size_t... I>
void ConstructFromTupleImpl(Alloc* alloc, T* ptr, Tuple&& t,
                            absl::index_sequence<I...>) {
  absl::allocator_traits<Alloc>::construct(
      *alloc, ptr, std::get<I>(std::forward<Tuple>(t))...);
}

template <class T, class F>
struct WithConstructedImplF {
  template <class... Args>
  decltype(std::declval<F>()(std::declval<T>())) operator()(
      Args&&... args) const {
    return std::forward<F>(f)(T(std::forward<Args>(args)...));
  }
  F&& f;
};

template <class T, class Tuple, size_t... Is, class F>
decltype(std::declval<F>()(std::declval<T>())) WithConstructedImpl(
    Tuple&& t, absl::index_sequence<Is...>, F&& f) {
  return WithConstructedImplF<T, F>{std::forward<F>(f)}(
      std::get<Is>(std::forward<Tuple>(t))...);
}

template <class T, size_t... Is>
auto TupleRefImpl(T&& t, absl::index_sequence<Is...>)
    -> decltype(std::forward_as_tuple(std::get<Is>(std::forward<T>(t))...)) {
  return std::forward_as_tuple(std::get<Is>(std::forward<T>(t))...);
}

// Returns a tuple of references to the elements of the input tuple. T must be a
// tuple.
template <class T>
auto TupleRef(T&& t) -> decltype(
    TupleRefImpl(std::forward<T>(t),
                 absl::make_index_sequence<
                     std::tuple_size<typename std::decay<T>::type>::value>())) {
  return TupleRefImpl(
      std::forward<T>(t),
      absl::make_index_sequence<
          std::tuple_size<typename std::decay<T>::type>::value>());
}

template <class F, class K, class V>
decltype(std::declval<F>()(std::declval<const K&>(), std::piecewise_construct,
                           std::declval<std::tuple<K>>(), std::declval<V>()))
DecomposePairImpl(F&& f, std::pair<std::tuple<K>, V> p) {
  const auto& key = std::get<0>(p.first);
  return std::forward<F>(f)(key, std::piecewise_construct, std::move(p.first),
                            std::move(p.second));
}

}  // namespace memory_internal

// Constructs T into uninitialized storage pointed by `ptr` using the args
// specified in the tuple.
template <class Alloc, class T, class Tuple>
void ConstructFromTuple(Alloc* alloc, T* ptr, Tuple&& t) {
  memory_internal::ConstructFromTupleImpl(
      alloc, ptr, std::forward<Tuple>(t),
      absl::make_index_sequence<
          std::tuple_size<typename std::decay<Tuple>::type>::value>());
}

// Constructs T using the args specified in the tuple and calls F with the
// constructed value.
template <class T, class Tuple, class F>
decltype(std::declval<F>()(std::declval<T>())) WithConstructed(
    Tuple&& t, F&& f) {
  return memory_internal::WithConstructedImpl<T>(
      std::forward<Tuple>(t),
      absl::make_index_sequence<
          std::tuple_size<typename std::decay<Tuple>::type>::value>(),
      std::forward<F>(f));
}

// Given arguments of an std::pair's consructor, PairArgs() returns a pair of
// tuples with references to the passed arguments. The tuples contain
// constructor arguments for the first and the second elements of the pair.
//
// The following two snippets are equivalent.
//
// 1. std::pair<F, S> p(args...);
//
// 2. auto a = PairArgs(args...);
//    std::pair<F, S> p(std::piecewise_construct,
//                      std::move(p.first), std::move(p.second));
inline std::pair<std::tuple<>, std::tuple<>> PairArgs() { return {}; }
template <class F, class S>
std::pair<std::tuple<F&&>, std::tuple<S&&>> PairArgs(F&& f, S&& s) {
  return {std::piecewise_construct, std::forward_as_tuple(std::forward<F>(f)),
          std::forward_as_tuple(std::forward<S>(s))};
}
template <class F, class S>
std::pair<std::tuple<const F&>, std::tuple<const S&>> PairArgs(
    const std::pair<F, S>& p) {
  return PairArgs(p.first, p.second);
}
template <class F, class S>
std::pair<std::tuple<F&&>, std::tuple<S&&>> PairArgs(std::pair<F, S>&& p) {
  return PairArgs(std::forward<F>(p.first), std::forward<S>(p.second));
}
template <class F, class S>
auto PairArgs(std::piecewise_construct_t, F&& f, S&& s)
    -> decltype(std::make_pair(memory_internal::TupleRef(std::forward<F>(f)),
                               memory_internal::TupleRef(std::forward<S>(s)))) {
  return std::make_pair(memory_internal::TupleRef(std::forward<F>(f)),
                        memory_internal::TupleRef(std::forward<S>(s)));
}

// A helper function for implementing apply() in map policies.
template <class F, class... Args>
auto DecomposePair(F&& f, Args&&... args)
    -> decltype(memory_internal::DecomposePairImpl(
        std::forward<F>(f), PairArgs(std::forward<Args>(args)...))) {
  return memory_internal::DecomposePairImpl(
      std::forward<F>(f), PairArgs(std::forward<Args>(args)...));
}

// A helper function for implementing apply() in set policies.
template <class F, class Arg>
decltype(std::declval<F>()(std::declval<const Arg&>(), std::declval<Arg>()))
DecomposeValue(F&& f, Arg&& arg) {
  const auto& key = arg;
  return std::forward<F>(f)(key, std::forward<Arg>(arg));
}

// Helper functions for asan and msan.
inline void SanitizerPoisonMemoryRegion(const void* m, size_t s) {
#ifdef ADDRESS_SANITIZER
  ASAN_POISON_MEMORY_REGION(m, s);
#endif
#ifdef MEMORY_SANITIZER
  __msan_poison(m, s);
#endif
  (void)m;
  (void)s;
}

inline void SanitizerUnpoisonMemoryRegion(const void* m, size_t s) {
#ifdef ADDRESS_SANITIZER
  ASAN_UNPOISON_MEMORY_REGION(m, s);
#endif
#ifdef MEMORY_SANITIZER
  __msan_unpoison(m, s);
#endif
  (void)m;
  (void)s;
}

template <typename T>
inline void SanitizerPoisonObject(const T* object) {
  SanitizerPoisonMemoryRegion(object, sizeof(T));
}

template <typename T>
inline void SanitizerUnpoisonObject(const T* object) {
  SanitizerUnpoisonMemoryRegion(object, sizeof(T));
}

namespace memory_internal {

// If Pair is a standard-layout type, OffsetOf<Pair>::kFirst and
// OffsetOf<Pair>::kSecond are equivalent to offsetof(Pair, first) and
// offsetof(Pair, second) respectively. Otherwise they are -1.
//
// The purpose of OffsetOf is to avoid calling offsetof() on non-standard-layout
// type, which is non-portable.
template <class Pair, class = std::true_type>
struct OffsetOf {
  static constexpr size_t kFirst = -1;
  static constexpr size_t kSecond = -1;
};

template <class Pair>
struct OffsetOf<Pair, typename std::is_standard_layout<Pair>::type> {
  static constexpr size_t kFirst = offsetof(Pair, first);
  static constexpr size_t kSecond = offsetof(Pair, second);
};

template <class K, class V>
struct IsLayoutCompatible {
 private:
  struct Pair {
    K first;
    V second;
  };

  // Is P layout-compatible with Pair?
  template <class P>
  static constexpr bool LayoutCompatible() {
    return std::is_standard_layout<P>() && sizeof(P) == sizeof(Pair) &&
           alignof(P) == alignof(Pair) &&
           memory_internal::OffsetOf<P>::kFirst ==
               memory_internal::OffsetOf<Pair>::kFirst &&
           memory_internal::OffsetOf<P>::kSecond ==
               memory_internal::OffsetOf<Pair>::kSecond;
  }

 public:
  // Whether pair<const K, V> and pair<K, V> are layout-compatible. If they are,
  // then it is safe to store them in a union and read from either.
  static constexpr bool value = std::is_standard_layout<K>() &&
                                std::is_standard_layout<Pair>() &&
                                memory_internal::OffsetOf<Pair>::kFirst == 0 &&
                                LayoutCompatible<std::pair<K, V>>() &&
                                LayoutCompatible<std::pair<const K, V>>();
};

}  // namespace memory_internal

// The internal storage type for key-value containers like flat_hash_map.
//
// It is convenient for the value_type of a flat_hash_map<K, V> to be
// pair<const K, V>; the "const K" prevents accidental modification of the key
// when dealing with the reference returned from find() and similar methods.
// However, this creates other problems; we want to be able to emplace(K, V)
// efficiently with move operations, and similarly be able to move a
// pair<K, V> in insert().
//
// The solution is this union, which aliases the const and non-const versions
// of the pair. This also allows flat_hash_map<const K, V> to work, even though
// that has the same efficiency issues with move in emplace() and insert() -
// but people do it anyway.
//
// If kMutableKeys is false, only the value member can be accessed.
//
// If kMutableKeys is true, key can be accessed through all slots while value
// and mutable_value must be accessed only via INITIALIZED slots. Slots are
// created and destroyed via mutable_value so that the key can be moved later.
//
// Accessing one of the union fields while the other is active is safe as
// long as they are layout-compatible, which is guaranteed by the definition of
// kMutableKeys. For C++11, the relevant section of the standard is
// https://timsong-cpp.github.io/cppwp/n3337/class.mem#19 (9.2.19)
template <class K, class V>
union map_slot_type {
  map_slot_type() {}
  ~map_slot_type() = delete;
  using value_type = std::pair<const K, V>;
  using mutable_value_type = std::pair<K, V>;

  value_type value;
  mutable_value_type mutable_value;
  K key;
};

template <class K, class V>
struct map_slot_policy {
  using slot_type = map_slot_type<K, V>;
  using value_type = std::pair<const K, V>;
  using mutable_value_type = std::pair<K, V>;

 private:
  static void emplace(slot_type* slot) {
    // The construction of union doesn't do anything at runtime but it allows us
    // to access its members without violating aliasing rules.
    new (slot) slot_type;
  }
  // If pair<const K, V> and pair<K, V> are layout-compatible, we can accept one
  // or the other via slot_type. We are also free to access the key via
  // slot_type::key in this case.
  using kMutableKeys = memory_internal::IsLayoutCompatible<K, V>;

 public:
  static value_type& element(slot_type* slot) { return slot->value; }
  static const value_type& element(const slot_type* slot) {
    return slot->value;
  }

  static const K& key(const slot_type* slot) {
    return kMutableKeys::value ? slot->key : slot->value.first;
  }

  template <class Allocator, class... Args>
  static void construct(Allocator* alloc, slot_type* slot, Args&&... args) {
    emplace(slot);
    if (kMutableKeys::value) {
      absl::allocator_traits<Allocator>::construct(*alloc, &slot->mutable_value,
                                                   std::forward<Args>(args)...);
    } else {
      absl::allocator_traits<Allocator>::construct(*alloc, &slot->value,
                                                   std::forward<Args>(args)...);
    }
  }

  // Construct this slot by moving from another slot.
  template <class Allocator>
  static void construct(Allocator* alloc, slot_type* slot, slot_type* other) {
    emplace(slot);
    if (kMutableKeys::value) {
      absl::allocator_traits<Allocator>::construct(
          *alloc, &slot->mutable_value, std::move(other->mutable_value));
    } else {
      absl::allocator_traits<Allocator>::construct(*alloc, &slot->value,
                                                   std::move(other->value));
    }
  }

  template <class Allocator>
  static void destroy(Allocator* alloc, slot_type* slot) {
    if (kMutableKeys::value) {
      absl::allocator_traits<Allocator>::destroy(*alloc, &slot->mutable_value);
    } else {
      absl::allocator_traits<Allocator>::destroy(*alloc, &slot->value);
    }
  }

  template <class Allocator>
  static void transfer(Allocator* alloc, slot_type* new_slot,
                       slot_type* old_slot) {
    emplace(new_slot);
    if (kMutableKeys::value) {
      absl::allocator_traits<Allocator>::construct(
          *alloc, &new_slot->mutable_value, std::move(old_slot->mutable_value));
    } else {
      absl::allocator_traits<Allocator>::construct(*alloc, &new_slot->value,
                                                   std::move(old_slot->value));
    }
    destroy(alloc, old_slot);
  }

  template <class Allocator>
  static void swap(Allocator* alloc, slot_type* a, slot_type* b) {
    if (kMutableKeys::value) {
      using std::swap;
      swap(a->mutable_value, b->mutable_value);
    } else {
      value_type tmp = std::move(a->value);
      absl::allocator_traits<Allocator>::destroy(*alloc, &a->value);
      absl::allocator_traits<Allocator>::construct(*alloc, &a->value,
                                                   std::move(b->value));
      absl::allocator_traits<Allocator>::destroy(*alloc, &b->value);
      absl::allocator_traits<Allocator>::construct(*alloc, &b->value,
                                                   std::move(tmp));
    }
  }

  template <class Allocator>
  static void move(Allocator* alloc, slot_type* src, slot_type* dest) {
    if (kMutableKeys::value) {
      dest->mutable_value = std::move(src->mutable_value);
    } else {
      absl::allocator_traits<Allocator>::destroy(*alloc, &dest->value);
      absl::allocator_traits<Allocator>::construct(*alloc, &dest->value,
                                                   std::move(src->value));
    }
  }

  template <class Allocator>
  static void move(Allocator* alloc, slot_type* first, slot_type* last,
                   slot_type* result) {
    for (slot_type *src = first, *dest = result; src != last; ++src, ++dest)
      move(alloc, src, dest);
  }
};

}  // namespace container_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_CONTAINER_INTERNAL_CONTAINER_MEMORY_H_