| // Protocol Buffers - Google's data interchange format |
| // Copyright 2008 Google Inc. All rights reserved. |
| // https://developers.google.com/protocol-buffers/ |
| // |
| // Redistribution and use in source and binary forms, with or without |
| // modification, are permitted provided that the following conditions are |
| // met: |
| // |
| // * Redistributions of source code must retain the above copyright |
| // notice, this list of conditions and the following disclaimer. |
| // * Redistributions in binary form must reproduce the above |
| // copyright notice, this list of conditions and the following disclaimer |
| // in the documentation and/or other materials provided with the |
| // distribution. |
| // * Neither the name of Google Inc. nor the names of its |
| // contributors may be used to endorse or promote products derived from |
| // this software without specific prior written permission. |
| // |
| // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| |
| #ifndef GOOGLE_PROTOBUF_ARENASTRING_H__ |
| #define GOOGLE_PROTOBUF_ARENASTRING_H__ |
| |
| #include <string> |
| #include <type_traits> |
| #include <utility> |
| |
| #include <google/protobuf/stubs/logging.h> |
| #include <google/protobuf/stubs/common.h> |
| #include <google/protobuf/arena.h> |
| #include <google/protobuf/port.h> |
| |
| #include <google/protobuf/port_def.inc> |
| |
| #ifdef SWIG |
| #error "You cannot SWIG proto headers" |
| #endif |
| |
| |
| namespace google { |
| namespace protobuf { |
| namespace internal { |
| |
| template <typename T> |
| class ExplicitlyConstructed; |
| |
| // Lazy string instance to support string fields with non-empty default. |
| // These are initialized on the first call to .get(). |
| class PROTOBUF_EXPORT LazyString { |
| public: |
| // We explicitly make LazyString an aggregate so that MSVC can do constant |
| // initialization on it without marking it `constexpr`. |
| // We do not want to use `constexpr` because it makes it harder to have extern |
| // storage for it and causes library bloat. |
| struct InitValue { |
| const char* ptr; |
| size_t size; |
| }; |
| // We keep a union of the initialization value and the std::string to save on |
| // space. We don't need the string array after Init() is done. |
| union { |
| mutable InitValue init_value_; |
| alignas(std::string) mutable char string_buf_[sizeof(std::string)]; |
| }; |
| mutable std::atomic<const std::string*> inited_; |
| |
| const std::string& get() const { |
| // This check generates less code than a call-once invocation. |
| auto* res = inited_.load(std::memory_order_acquire); |
| if (PROTOBUF_PREDICT_FALSE(res == nullptr)) return Init(); |
| return *res; |
| } |
| |
| private: |
| // Initialize the string in `string_buf_`, update `inited_` and return it. |
| // We return it here to avoid having to read it again in the inlined code. |
| const std::string& Init() const; |
| }; |
| |
| template <typename T> |
| class TaggedPtr { |
| public: |
| TaggedPtr() = default; |
| explicit constexpr TaggedPtr(const ExplicitlyConstructed<std::string>* ptr) |
| : ptr_(const_cast<ExplicitlyConstructed<std::string>*>(ptr)) {} |
| |
| void SetTagged(T* p) { |
| Set(p); |
| ptr_ = reinterpret_cast<void*>(as_int() | 1); |
| } |
| void Set(T* p) { ptr_ = p; } |
| T* Get() const { return reinterpret_cast<T*>(as_int() & -2); } |
| bool IsTagged() const { return as_int() & 1; } |
| |
| // Returned value is only safe to dereference if IsTagged() == false. |
| // It is safe to compare. |
| T* UnsafeGet() const { return static_cast<T*>(ptr_); } |
| |
| bool IsNull() { return ptr_ == nullptr; } |
| |
| private: |
| uintptr_t as_int() const { return reinterpret_cast<uintptr_t>(ptr_); } |
| void* ptr_; |
| }; |
| |
| static_assert(std::is_trivial<TaggedPtr<std::string>>::value, |
| "TaggedPtr must be trivial"); |
| |
| // This class encapsulates a pointer to a std::string with or without a donated |
| // buffer, tagged by bottom bit. It is a high-level wrapper that almost directly |
| // corresponds to the interface required by string fields in generated |
| // code. It replaces the old std::string* pointer in such cases. |
| // |
| // The object has different but similar code paths for when the default value is |
| // the empty string and when it is a non-empty string. |
| // The empty string is handled different throughout the library and there is a |
| // single global instance of it we can share. |
| // |
| // For fields with an empty string default value, there are three distinct |
| // states: |
| // |
| // - Pointer set to 'String' tag (LSB is 0), equal to |
| // &GetEmptyStringAlreadyInited(): field is set to its default value. Points |
| // to a true std::string*, but we do not own that std::string* (it's a |
| // globally shared instance). |
| // |
| // - Pointer set to 'String' tag (LSB is 0), but not equal to the global empty |
| // string: field points to a true std::string* instance that we own. This |
| // instance is either on the heap or on the arena (i.e. registered on |
| // free()/destructor-call list) as appropriate. |
| // |
| // - Pointer set to 'DonatedString' tag (LSB is 1): points to a std::string |
| // instance with a buffer on the arena (arena != NULL, always, in this case). |
| // |
| // For fields with a non-empty string default value, there are three distinct |
| // states: |
| // |
| // - Pointer set to 'String' tag (LSB is 0), equal to `nullptr`: |
| // Field is in "default" mode and does not point to any actual instance. |
| // Methods that might need to create an instance of the object will pass a |
| // `const LazyString&` for it. |
| // |
| // - Pointer set to 'String' tag (LSB is 0), but not equal to `nullptr`: |
| // field points to a true std::string* instance that we own. This instance is |
| // either on the heap or on the arena (i.e. registered on |
| // free()/destructor-call list) as appropriate. |
| // |
| // - Pointer set to 'DonatedString' tag (LSB is 1): points to a std::string |
| // instance with a buffer on the arena (arena != NULL, always, in this case). |
| // |
| // Generated code and reflection code both ensure that ptr_ is never null for |
| // fields with an empty default. |
| // Because ArenaStringPtr is used in oneof unions, its constructor is a NOP and |
| // so the field is always manually initialized via method calls. |
| // |
| // Side-note: why pass information about the default on every API call? Because |
| // we don't want to hold it in a member variable, or else this would go into |
| // every proto message instance. This would be a huge waste of space, since the |
| // default instance pointer is typically a global (static class field). We want |
| // the generated code to be as efficient as possible, and if we take |
| // the default value information as a parameter that's in practice taken from a |
| // static class field, and compare ptr_ to the default value, we end up with a |
| // single "cmp %reg, GLOBAL" in the resulting machine code. (Note that this also |
| // requires the String tag to be 0 so we can avoid the mask before comparing.) |
| struct PROTOBUF_EXPORT ArenaStringPtr { |
| ArenaStringPtr() = default; |
| explicit constexpr ArenaStringPtr( |
| const ExplicitlyConstructed<std::string>* default_value) |
| : tagged_ptr_(default_value) {} |
| |
| // Some methods below are overloaded on a `default_value` and on tags. |
| // The tagged overloads help reduce code size in the callers in generated |
| // code, while the `default_value` overloads are useful from reflection. |
| // By-value empty struct arguments are elided in the ABI. |
| struct EmptyDefault {}; |
| struct NonEmptyDefault {}; |
| |
| void Set(const std::string* default_value, ConstStringParam value, |
| ::google::protobuf::Arena* arena); |
| void Set(const std::string* default_value, std::string&& value, |
| ::google::protobuf::Arena* arena); |
| void Set(EmptyDefault, ConstStringParam value, ::google::protobuf::Arena* arena); |
| void Set(EmptyDefault, std::string&& value, ::google::protobuf::Arena* arena); |
| void Set(NonEmptyDefault, ConstStringParam value, ::google::protobuf::Arena* arena); |
| void Set(NonEmptyDefault, std::string&& value, ::google::protobuf::Arena* arena); |
| template <typename FirstParam> |
| void Set(FirstParam p1, const char* str, ::google::protobuf::Arena* arena) { |
| Set(p1, ConstStringParam(str), arena); |
| } |
| template <typename FirstParam> |
| void Set(FirstParam p1, const char* str, size_t size, |
| ::google::protobuf::Arena* arena) { |
| ConstStringParam sp{str, size}; // for string_view and `const string &` |
| Set(p1, sp, arena); |
| } |
| template <typename FirstParam, typename RefWrappedType> |
| void Set(FirstParam p1, |
| std::reference_wrapper<RefWrappedType> const_string_ref, |
| ::google::protobuf::Arena* arena) { |
| Set(p1, const_string_ref.get(), arena); |
| } |
| |
| template <typename FirstParam, typename SecondParam> |
| void SetBytes(FirstParam p1, SecondParam&& p2, ::google::protobuf::Arena* arena) { |
| Set(p1, static_cast<SecondParam&&>(p2), arena); |
| } |
| template <typename FirstParam> |
| void SetBytes(FirstParam p1, const void* str, size_t size, |
| ::google::protobuf::Arena* arena) { |
| // must work whether ConstStringParam is string_view or `const string &` |
| ConstStringParam sp{static_cast<const char*>(str), size}; |
| Set(p1, sp, arena); |
| } |
| |
| // Basic accessors. |
| PROTOBUF_NDEBUG_INLINE const std::string& Get() const { |
| // Unconditionally mask away the tag. |
| return *tagged_ptr_.Get(); |
| } |
| PROTOBUF_NDEBUG_INLINE const std::string* GetPointer() const { |
| // Unconditionally mask away the tag. |
| return tagged_ptr_.Get(); |
| } |
| |
| // For fields with an empty default value. |
| std::string* Mutable(EmptyDefault, ::google::protobuf::Arena* arena); |
| // For fields with a non-empty default value. |
| std::string* Mutable(const LazyString& default_value, ::google::protobuf::Arena* arena); |
| |
| // Release returns a std::string* instance that is heap-allocated and is not |
| // Own()'d by any arena. If the field is not set, this returns NULL. The |
| // caller retains ownership. Clears this field back to NULL state. Used to |
| // implement release_<field>() methods on generated classes. |
| PROTOBUF_FUTURE_MUST_USE_RESULT std::string* Release( |
| const std::string* default_value, ::google::protobuf::Arena* arena); |
| PROTOBUF_FUTURE_MUST_USE_RESULT std::string* ReleaseNonDefault( |
| const std::string* default_value, ::google::protobuf::Arena* arena); |
| |
| // Takes a std::string that is heap-allocated, and takes ownership. The |
| // std::string's destructor is registered with the arena. Used to implement |
| // set_allocated_<field> in generated classes. |
| void SetAllocated(const std::string* default_value, std::string* value, |
| ::google::protobuf::Arena* arena); |
| |
| // Swaps internal pointers. Arena-safety semantics: this is guarded by the |
| // logic in Swap()/UnsafeArenaSwap() at the message level, so this method is |
| // 'unsafe' if called directly. |
| inline PROTOBUF_NDEBUG_INLINE static void InternalSwap( |
| const std::string* default_value, ArenaStringPtr* rhs, Arena* rhs_arena, |
| ArenaStringPtr* lhs, Arena* lhs_arena); |
| |
| // Frees storage (if not on an arena). |
| void Destroy(const std::string* default_value, ::google::protobuf::Arena* arena); |
| void Destroy(EmptyDefault, ::google::protobuf::Arena* arena); |
| void Destroy(NonEmptyDefault, ::google::protobuf::Arena* arena); |
| |
| // Clears content, but keeps allocated std::string, to avoid the overhead of |
| // heap operations. After this returns, the content (as seen by the user) will |
| // always be the empty std::string. Assumes that |default_value| is an empty |
| // std::string. |
| void ClearToEmpty(); |
| |
| // Clears content, assuming that the current value is not the empty |
| // string default. |
| void ClearNonDefaultToEmpty(); |
| |
| // Clears content, but keeps allocated std::string if arena != NULL, to avoid |
| // the overhead of heap operations. After this returns, the content (as seen |
| // by the user) will always be equal to |default_value|. |
| void ClearToDefault(const LazyString& default_value, ::google::protobuf::Arena* arena); |
| |
| // Called from generated code / reflection runtime only. Resets value to point |
| // to a default string pointer, with the semantics that this |
| // ArenaStringPtr does not own the pointed-to memory. Disregards initial value |
| // of ptr_ (so this is the *ONLY* safe method to call after construction or |
| // when reinitializing after becoming the active field in a oneof union). |
| inline void UnsafeSetDefault(const std::string* default_value); |
| |
| // Returns a mutable pointer, but doesn't initialize the string to the |
| // default value. |
| std::string* MutableNoArenaNoDefault(const std::string* default_value); |
| |
| // Get a mutable pointer with unspecified contents. |
| // Similar to `MutableNoArenaNoDefault`, but also handles the arena case. |
| // If the value was donated, the contents are discarded. |
| std::string* MutableNoCopy(const std::string* default_value, |
| ::google::protobuf::Arena* arena); |
| |
| // Destroy the string. Assumes `arena == nullptr`. |
| void DestroyNoArena(const std::string* default_value); |
| |
| // Internal setter used only at parse time to directly set a donated string |
| // value. |
| void UnsafeSetTaggedPointer(TaggedPtr<std::string> value) { |
| tagged_ptr_ = value; |
| } |
| // Generated code only! An optimization, in certain cases the generated |
| // code is certain we can obtain a std::string with no default checks and |
| // tag tests. |
| std::string* UnsafeMutablePointer() PROTOBUF_RETURNS_NONNULL; |
| |
| inline bool IsDefault(const std::string* default_value) const { |
| // Relies on the fact that kPtrTagString == 0, so if IsString(), ptr_ is the |
| // actual std::string pointer (and if !IsString(), ptr_ will never be equal |
| // to any aligned |default_value| pointer). The key is that we want to avoid |
| // masking in the fastpath const-pointer Get() case for non-arena code. |
| return tagged_ptr_.UnsafeGet() == default_value; |
| } |
| |
| private: |
| TaggedPtr<std::string> tagged_ptr_; |
| |
| bool IsDonatedString() const { return false; } |
| |
| // Slow paths. |
| |
| // MutableSlow requires that !IsString() || IsDefault |
| // Variadic to support 0 args for EmptyDefault and 1 arg for LazyString. |
| template <typename... Lazy> |
| std::string* MutableSlow(::google::protobuf::Arena* arena, const Lazy&... lazy_default); |
| |
| // Sets value to a newly allocated string and returns it |
| std::string* SetAndReturnNewString(); |
| |
| // Destroys the non-default string value out-of-line |
| void DestroyNoArenaSlowPath(); |
| |
| }; |
| |
| inline void ArenaStringPtr::UnsafeSetDefault(const std::string* value) { |
| tagged_ptr_.Set(const_cast<std::string*>(value)); |
| } |
| |
| inline PROTOBUF_NDEBUG_INLINE void ArenaStringPtr::InternalSwap( // |
| const std::string* default_value, // |
| ArenaStringPtr* rhs, Arena* rhs_arena, // |
| ArenaStringPtr* lhs, Arena* lhs_arena) { |
| (void)default_value; |
| std::swap(lhs_arena, rhs_arena); |
| std::swap(lhs->tagged_ptr_, rhs->tagged_ptr_); |
| #if 0 // TODO(b/186650244): renable this |
| #ifndef NDEBUG |
| auto force_realloc = [default_value](ArenaStringPtr* p, Arena* arena) { |
| if (p->IsDefault(default_value)) return; |
| std::string* old_value = p->tagged_ptr_.Get(); |
| std::string* new_value = |
| p->IsDonatedString() |
| ? Arena::Create<std::string>(arena, *old_value) |
| : Arena::Create<std::string>(arena, std::move(*old_value)); |
| if (arena == nullptr) delete old_value; |
| p->tagged_ptr_.Set(new_value); |
| }; |
| force_realloc(lhs, lhs_arena); |
| force_realloc(rhs, rhs_arena); |
| #endif |
| #endif |
| } |
| |
| inline void ArenaStringPtr::ClearNonDefaultToEmpty() { |
| // Unconditionally mask away the tag. |
| tagged_ptr_.Get()->clear(); |
| } |
| |
| inline std::string* ArenaStringPtr::MutableNoArenaNoDefault( |
| const std::string* default_value) { |
| // VERY IMPORTANT for performance and code size: this will reduce to a member |
| // variable load, a pointer check (against |default_value|, in practice a |
| // static global) and a branch to the slowpath (which calls operator new and |
| // the ctor). DO NOT add any tagged-pointer operations here. |
| if (IsDefault(default_value)) { |
| return SetAndReturnNewString(); |
| } else { |
| return UnsafeMutablePointer(); |
| } |
| } |
| |
| inline void ArenaStringPtr::DestroyNoArena(const std::string* default_value) { |
| if (!IsDefault(default_value)) { |
| DestroyNoArenaSlowPath(); |
| } |
| } |
| |
| inline std::string* ArenaStringPtr::UnsafeMutablePointer() { |
| GOOGLE_DCHECK(!tagged_ptr_.IsTagged()); |
| GOOGLE_DCHECK(tagged_ptr_.UnsafeGet() != nullptr); |
| return tagged_ptr_.UnsafeGet(); |
| } |
| |
| |
| } // namespace internal |
| } // namespace protobuf |
| } // namespace google |
| |
| #include <google/protobuf/port_undef.inc> |
| |
| #endif // GOOGLE_PROTOBUF_ARENASTRING_H__ |