1// Protocol Buffers - Google's data interchange format
2// Copyright 2008 Google Inc. All rights reserved.
3// https://developers.google.com/protocol-buffers/
4//
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6// modification, are permitted provided that the following conditions are
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8//
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10// notice, this list of conditions and the following disclaimer.
11// * Redistributions in binary form must reproduce the above
12// copyright notice, this list of conditions and the following disclaimer
13// in the documentation and/or other materials provided with the
14// distribution.
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16// contributors may be used to endorse or promote products derived from
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18//
19// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
20// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
21// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
22// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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28// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
29// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30
31#ifndef GOOGLE_PROTOBUF_ARENASTRING_H__
32#define GOOGLE_PROTOBUF_ARENASTRING_H__
33
34#include <string>
35#include <type_traits>
36#include <utility>
37
38#include <google/protobuf/stubs/logging.h>
39#include <google/protobuf/stubs/common.h>
40#include <google/protobuf/arena.h>
41#include <google/protobuf/port.h>
42
43#include <google/protobuf/port_def.inc>
44
45#ifdef SWIG
46#error "You cannot SWIG proto headers"
47#endif
48
49
50namespace google {
51namespace protobuf {
52namespace internal {
53
54template <typename T>
55class ExplicitlyConstructed;
56
57class SwapFieldHelper;
58
59// Lazy string instance to support string fields with non-empty default.
60// These are initialized on the first call to .get().
61class PROTOBUF_EXPORT LazyString {
62 public:
63 // We explicitly make LazyString an aggregate so that MSVC can do constant
64 // initialization on it without marking it `constexpr`.
65 // We do not want to use `constexpr` because it makes it harder to have extern
66 // storage for it and causes library bloat.
67 struct InitValue {
68 const char* ptr;
69 size_t size;
70 };
71 // We keep a union of the initialization value and the std::string to save on
72 // space. We don't need the string array after Init() is done.
73 union {
74 mutable InitValue init_value_;
75 alignas(std::string) mutable char string_buf_[sizeof(std::string)];
76 };
77 mutable std::atomic<const std::string*> inited_;
78
79 const std::string& get() const {
80 // This check generates less code than a call-once invocation.
81 auto* res = inited_.load(m: std::memory_order_acquire);
82 if (PROTOBUF_PREDICT_FALSE(res == nullptr)) return Init();
83 return *res;
84 }
85
86 private:
87 // Initialize the string in `string_buf_`, update `inited_` and return it.
88 // We return it here to avoid having to read it again in the inlined code.
89 const std::string& Init() const;
90};
91
92template <typename T>
93class TaggedPtr {
94 public:
95 TaggedPtr() = default;
96 explicit constexpr TaggedPtr(const ExplicitlyConstructed<std::string>* ptr)
97 : ptr_(const_cast<ExplicitlyConstructed<std::string>*>(ptr)) {}
98
99 void SetTagged(T* p) {
100 Set(p);
101 ptr_ = reinterpret_cast<void*>(as_int() | 1);
102 }
103 void Set(T* p) { ptr_ = p; }
104 T* Get() const { return reinterpret_cast<T*>(as_int() & -2); }
105 bool IsTagged() const { return as_int() & 1; }
106
107 // Returned value is only safe to dereference if IsTagged() == false.
108 // It is safe to compare.
109 T* UnsafeGet() const { return static_cast<T*>(ptr_); }
110
111 bool IsNull() { return ptr_ == nullptr; }
112
113 private:
114 uintptr_t as_int() const { return reinterpret_cast<uintptr_t>(ptr_); }
115 void* ptr_;
116};
117
118static_assert(std::is_trivial<TaggedPtr<std::string>>::value,
119 "TaggedPtr must be trivial");
120
121// This class encapsulates a pointer to a std::string with or without a donated
122// buffer, tagged by bottom bit. It is a high-level wrapper that almost directly
123// corresponds to the interface required by string fields in generated
124// code. It replaces the old std::string* pointer in such cases.
125//
126// The object has different but similar code paths for when the default value is
127// the empty string and when it is a non-empty string.
128// The empty string is handled different throughout the library and there is a
129// single global instance of it we can share.
130//
131// For fields with an empty string default value, there are three distinct
132// states:
133//
134// - Pointer set to 'String' tag (LSB is 0), equal to
135// &GetEmptyStringAlreadyInited(): field is set to its default value. Points
136// to a true std::string*, but we do not own that std::string* (it's a
137// globally shared instance).
138//
139// - Pointer set to 'String' tag (LSB is 0), but not equal to the global empty
140// string: field points to a true std::string* instance that we own. This
141// instance is either on the heap or on the arena (i.e. registered on
142// free()/destructor-call list) as appropriate.
143//
144// - Pointer set to 'DonatedString' tag (LSB is 1): points to a std::string
145// instance with a buffer on the arena (arena is never nullptr in this case).
146//
147// For fields with a non-empty string default value, there are three distinct
148// states:
149//
150// - Pointer set to 'String' tag (LSB is 0), equal to `nullptr`:
151// Field is in "default" mode and does not point to any actual instance.
152// Methods that might need to create an instance of the object will pass a
153// `const LazyString&` for it.
154//
155// - Pointer set to 'String' tag (LSB is 0), but not equal to `nullptr`:
156// field points to a true std::string* instance that we own. This instance is
157// either on the heap or on the arena (i.e. registered on
158// free()/destructor-call list) as appropriate.
159//
160// - Pointer set to 'DonatedString' tag (LSB is 1): points to a std::string
161// instance with a buffer on the arena (arena is never nullptr in this case).
162//
163// Generated code and reflection code both ensure that ptr_ is never null for
164// fields with an empty default.
165// Because ArenaStringPtr is used in oneof unions, its constructor is a NOP and
166// so the field is always manually initialized via method calls.
167//
168// Side-note: why pass information about the default on every API call? Because
169// we don't want to hold it in a member variable, or else this would go into
170// every proto message instance. This would be a huge waste of space, since the
171// default instance pointer is typically a global (static class field). We want
172// the generated code to be as efficient as possible, and if we take
173// the default value information as a parameter that's in practice taken from a
174// static class field, and compare ptr_ to the default value, we end up with a
175// single "cmp %reg, GLOBAL" in the resulting machine code. (Note that this also
176// requires the String tag to be 0 so we can avoid the mask before comparing.)
177struct PROTOBUF_EXPORT ArenaStringPtr {
178 ArenaStringPtr() = default;
179 explicit constexpr ArenaStringPtr(
180 const ExplicitlyConstructed<std::string>* default_value)
181 : tagged_ptr_(default_value) {}
182
183 // Some methods below are overloaded on a `default_value` and on tags.
184 // The tagged overloads help reduce code size in the callers in generated
185 // code, while the `default_value` overloads are useful from reflection.
186 // By-value empty struct arguments are elided in the ABI.
187 struct EmptyDefault {};
188 struct NonEmptyDefault {};
189
190 void Set(const std::string* default_value, ConstStringParam value,
191 ::google::protobuf::Arena* arena);
192 void Set(const std::string* default_value, std::string&& value,
193 ::google::protobuf::Arena* arena);
194 void Set(EmptyDefault, ConstStringParam value, ::google::protobuf::Arena* arena);
195 void Set(EmptyDefault, std::string&& value, ::google::protobuf::Arena* arena);
196 void Set(NonEmptyDefault, ConstStringParam value, ::google::protobuf::Arena* arena);
197 void Set(NonEmptyDefault, std::string&& value, ::google::protobuf::Arena* arena);
198 template <typename FirstParam>
199 void Set(FirstParam p1, const char* str, ::google::protobuf::Arena* arena) {
200 Set(p1, ConstStringParam(str), arena);
201 }
202 template <typename FirstParam>
203 void Set(FirstParam p1, const char* str, size_t size,
204 ::google::protobuf::Arena* arena) {
205 ConstStringParam sp{str, size}; // for string_view and `const string &`
206 Set(p1, sp, arena);
207 }
208 template <typename FirstParam, typename RefWrappedType>
209 void Set(FirstParam p1,
210 std::reference_wrapper<RefWrappedType> const_string_ref,
211 ::google::protobuf::Arena* arena) {
212 Set(p1, const_string_ref.get(), arena);
213 }
214
215 template <typename FirstParam, typename SecondParam>
216 void SetBytes(FirstParam p1, SecondParam&& p2, ::google::protobuf::Arena* arena) {
217 Set(p1, static_cast<SecondParam&&>(p2), arena);
218 }
219 template <typename FirstParam>
220 void SetBytes(FirstParam p1, const void* str, size_t size,
221 ::google::protobuf::Arena* arena) {
222 // must work whether ConstStringParam is string_view or `const string &`
223 ConstStringParam sp{static_cast<const char*>(str), size};
224 Set(p1, sp, arena);
225 }
226
227 // Basic accessors.
228 PROTOBUF_NDEBUG_INLINE const std::string& Get() const {
229 // Unconditionally mask away the tag.
230 return *tagged_ptr_.Get();
231 }
232 PROTOBUF_NDEBUG_INLINE const std::string* GetPointer() const {
233 // Unconditionally mask away the tag.
234 return tagged_ptr_.Get();
235 }
236
237 // For fields with an empty default value.
238 std::string* Mutable(EmptyDefault, ::google::protobuf::Arena* arena);
239 // For fields with a non-empty default value.
240 std::string* Mutable(const LazyString& default_value, ::google::protobuf::Arena* arena);
241
242 // Release returns a std::string* instance that is heap-allocated and is not
243 // Own()'d by any arena. If the field is not set, this returns nullptr. The
244 // caller retains ownership. Clears this field back to nullptr state. Used to
245 // implement release_<field>() methods on generated classes.
246 PROTOBUF_NODISCARD std::string* Release(const std::string* default_value,
247 ::google::protobuf::Arena* arena);
248 PROTOBUF_NODISCARD std::string* ReleaseNonDefault(
249 const std::string* default_value, ::google::protobuf::Arena* arena);
250
251 // Takes a std::string that is heap-allocated, and takes ownership. The
252 // std::string's destructor is registered with the arena. Used to implement
253 // set_allocated_<field> in generated classes.
254 void SetAllocated(const std::string* default_value, std::string* value,
255 ::google::protobuf::Arena* arena);
256
257 // Swaps internal pointers. Arena-safety semantics: this is guarded by the
258 // logic in Swap()/UnsafeArenaSwap() at the message level, so this method is
259 // 'unsafe' if called directly.
260 inline PROTOBUF_NDEBUG_INLINE static void InternalSwap(
261 const std::string* default_value, ArenaStringPtr* rhs, Arena* rhs_arena,
262 ArenaStringPtr* lhs, Arena* lhs_arena);
263
264 // Frees storage (if not on an arena).
265 void Destroy(const std::string* default_value, ::google::protobuf::Arena* arena);
266 void Destroy(EmptyDefault, ::google::protobuf::Arena* arena);
267 void Destroy(NonEmptyDefault, ::google::protobuf::Arena* arena);
268
269 // Clears content, but keeps allocated std::string, to avoid the overhead of
270 // heap operations. After this returns, the content (as seen by the user) will
271 // always be the empty std::string. Assumes that |default_value| is an empty
272 // std::string.
273 void ClearToEmpty();
274
275 // Clears content, assuming that the current value is not the empty
276 // string default.
277 void ClearNonDefaultToEmpty();
278
279 // Clears content, but keeps allocated std::string if arena != nullptr, to
280 // avoid the overhead of heap operations. After this returns, the content
281 // (as seen by the user) will always be equal to |default_value|.
282 void ClearToDefault(const LazyString& default_value, ::google::protobuf::Arena* arena);
283
284 // Called from generated code / reflection runtime only. Resets value to point
285 // to a default string pointer, with the semantics that this
286 // ArenaStringPtr does not own the pointed-to memory. Disregards initial value
287 // of ptr_ (so this is the *ONLY* safe method to call after construction or
288 // when reinitializing after becoming the active field in a oneof union).
289 inline void UnsafeSetDefault(const std::string* default_value);
290
291 // Returns a mutable pointer, but doesn't initialize the string to the
292 // default value.
293 std::string* MutableNoArenaNoDefault(const std::string* default_value);
294
295 // Get a mutable pointer with unspecified contents.
296 // Similar to `MutableNoArenaNoDefault`, but also handles the arena case.
297 // If the value was donated, the contents are discarded.
298 std::string* MutableNoCopy(const std::string* default_value,
299 ::google::protobuf::Arena* arena);
300
301 // Destroy the string. Assumes `arena == nullptr`.
302 void DestroyNoArena(const std::string* default_value);
303
304 // Internal setter used only at parse time to directly set a donated string
305 // value.
306 void UnsafeSetTaggedPointer(TaggedPtr<std::string> value) {
307 tagged_ptr_ = value;
308 }
309 // Generated code only! An optimization, in certain cases the generated
310 // code is certain we can obtain a std::string with no default checks and
311 // tag tests.
312 std::string* UnsafeMutablePointer() PROTOBUF_RETURNS_NONNULL;
313
314 inline bool IsDefault(const std::string* default_value) const {
315 // Relies on the fact that kPtrTagString == 0, so if IsString(), ptr_ is the
316 // actual std::string pointer (and if !IsString(), ptr_ will never be equal
317 // to any aligned |default_value| pointer). The key is that we want to avoid
318 // masking in the fastpath const-pointer Get() case for non-arena code.
319 return tagged_ptr_.UnsafeGet() == default_value;
320 }
321
322 private:
323 TaggedPtr<std::string> tagged_ptr_;
324
325 bool IsDonatedString() const { return false; }
326
327 // Swaps tagged pointer without debug hardening. This is to allow python
328 // protobuf to maintain pointer stability even in DEBUG builds.
329 inline PROTOBUF_NDEBUG_INLINE static void UnsafeShallowSwap(
330 ArenaStringPtr* rhs, ArenaStringPtr* lhs) {
331 std::swap(a&: lhs->tagged_ptr_, b&: rhs->tagged_ptr_);
332 }
333
334 friend class ::google::protobuf::internal::SwapFieldHelper;
335
336 // Slow paths.
337
338 // MutableSlow requires that !IsString() || IsDefault
339 // Variadic to support 0 args for EmptyDefault and 1 arg for LazyString.
340 template <typename... Lazy>
341 std::string* MutableSlow(::google::protobuf::Arena* arena, const Lazy&... lazy_default);
342
343 // Sets value to a newly allocated string and returns it
344 std::string* SetAndReturnNewString();
345
346 // Destroys the non-default string value out-of-line
347 void DestroyNoArenaSlowPath();
348
349};
350
351inline void ArenaStringPtr::UnsafeSetDefault(const std::string* value) {
352 tagged_ptr_.Set(const_cast<std::string*>(value));
353}
354
355// Make sure rhs_arena allocated rhs, and lhs_arena allocated lhs.
356inline PROTOBUF_NDEBUG_INLINE void ArenaStringPtr::InternalSwap( //
357 const std::string* default_value, //
358 ArenaStringPtr* rhs, Arena* rhs_arena, //
359 ArenaStringPtr* lhs, Arena* lhs_arena) {
360 // Silence unused variable warnings in release buildls.
361 (void)default_value;
362 (void)rhs_arena;
363 (void)lhs_arena;
364 std::swap(a&: lhs->tagged_ptr_, b&: rhs->tagged_ptr_);
365#ifdef PROTOBUF_FORCE_COPY_IN_SWAP
366 auto force_realloc = [default_value](ArenaStringPtr* p, Arena* arena) {
367 if (p->IsDefault(default_value)) return;
368 std::string* old_value = p->tagged_ptr_.Get();
369 std::string* new_value =
370 p->IsDonatedString()
371 ? Arena::Create<std::string>(arena, *old_value)
372 : Arena::Create<std::string>(arena, std::move(*old_value));
373 if (arena == nullptr) delete old_value;
374 p->tagged_ptr_.Set(new_value);
375 };
376 // Because, at this point, tagged_ptr_ has been swapped, arena should also be
377 // swapped.
378 force_realloc(lhs, rhs_arena);
379 force_realloc(rhs, lhs_arena);
380#endif // PROTOBUF_FORCE_COPY_IN_SWAP
381}
382
383inline void ArenaStringPtr::ClearNonDefaultToEmpty() {
384 // Unconditionally mask away the tag.
385 tagged_ptr_.Get()->clear();
386}
387
388inline std::string* ArenaStringPtr::MutableNoArenaNoDefault(
389 const std::string* default_value) {
390 // VERY IMPORTANT for performance and code size: this will reduce to a member
391 // variable load, a pointer check (against |default_value|, in practice a
392 // static global) and a branch to the slowpath (which calls operator new and
393 // the ctor). DO NOT add any tagged-pointer operations here.
394 if (IsDefault(default_value)) {
395 return SetAndReturnNewString();
396 } else {
397 return UnsafeMutablePointer();
398 }
399}
400
401inline void ArenaStringPtr::DestroyNoArena(const std::string* default_value) {
402 if (!IsDefault(default_value)) {
403 DestroyNoArenaSlowPath();
404 }
405}
406
407inline std::string* ArenaStringPtr::UnsafeMutablePointer() {
408 GOOGLE_DCHECK(!tagged_ptr_.IsTagged());
409 GOOGLE_DCHECK(tagged_ptr_.UnsafeGet() != nullptr);
410 return tagged_ptr_.UnsafeGet();
411}
412
413
414} // namespace internal
415} // namespace protobuf
416} // namespace google
417
418#include <google/protobuf/port_undef.inc>
419
420#endif // GOOGLE_PROTOBUF_ARENASTRING_H__
421

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source code of opencv/3rdparty/protobuf/src/google/protobuf/arenastring.h