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// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
//
// 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 <algorithm>
#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/explicitly_constructed.h>
// must be last:
#include <google/protobuf/port_def.inc>
#ifdef SWIG
#error "You cannot SWIG proto headers"
#endif
namespace google {
namespace protobuf {
namespace internal {
class EpsCopyInputStream;
class SwapFieldHelper;
// Declared in message_lite.h
PROTOBUF_EXPORT extern ExplicitlyConstructedArenaString
fixed_address_empty_string;
// 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;
};
class TaggedStringPtr {
public:
// Bit flags qualifying string properties. We can use 2 bits as
// ptr_ is guaranteed and enforced to be aligned on 4 byte boundaries.
enum Flags {
kArenaBit = 0x1, // ptr is arena allocated
kMutableBit = 0x2, // ptr contents are fully mutable
kMask = 0x3 // Bit mask
};
// Composed logical types
enum Type {
// Default strings are immutable and never owned.
kDefault = 0,
// Allocated strings are mutable and (as the name implies) owned.
// A heap allocated string must be deleted.
kAllocated = kMutableBit,
// Mutable arena strings are strings where the string instance is owned
// by the arena, but the string contents itself are owned by the string
// instance. Mutable arena string instances need to be destroyed which is
// typically done through a cleanup action added to the arena owning it.
kMutableArena = kArenaBit | kMutableBit,
// Fixed size arena strings are strings where both the string instance and
// the string contents are fully owned by the arena. Fixed size arena
// strings are a platform and c++ library specific customization. Fixed
// size arena strings are immutable, with the exception of custom internal
// updates to the content that fit inside the existing capacity.
// Fixed size arena strings must never be deleted or destroyed.
kFixedSizeArena = kArenaBit,
};
TaggedStringPtr() = default;
explicit constexpr TaggedStringPtr(ExplicitlyConstructedArenaString* ptr)
: ptr_(ptr) {}
// Sets the value to `p`, tagging the value as being a 'default' value.
// See documentation for kDefault for more info.
inline const std::string* SetDefault(const std::string* p) {
return TagAs(kDefault, const_cast<std::string*>(p));
}
// Sets the value to `p`, tagging the value as a heap allocated value.
// Allocated strings are mutable and (as the name implies) owned.
// `p` must not be null
inline std::string* SetAllocated(std::string* p) {
return TagAs(kAllocated, p);
}
// Sets the value to `p`, tagging the value as a fixed size arena string.
// See documentation for kFixedSizeArena for more info.
// `p` must not be null
inline std::string* SetFixedSizeArena(std::string* p) {
return TagAs(kFixedSizeArena, p);
}
// Sets the value to `p`, tagging the value as a mutable arena string.
// See documentation for kMutableArena for more info.
// `p` must not be null
inline std::string* SetMutableArena(std::string* p) {
return TagAs(kMutableArena, p);
}
// Returns true if the contents of the current string are fully mutable.
inline bool IsMutable() const { return as_int() & kMutableBit; }
// Returns true if the current string is an immutable default value.
inline bool IsDefault() const { return (as_int() & kMask) == kDefault; }
// If the current string is a heap-allocated mutable value, returns a pointer
// to it. Returns nullptr otherwise.
inline std::string *GetIfAllocated() const {
auto allocated = as_int() ^ kAllocated;
if (allocated & kMask) return nullptr;
auto ptr = reinterpret_cast<std::string*>(allocated);
PROTOBUF_ASSUME(ptr != nullptr);
return ptr;
}
// Returns true if the current string is an arena allocated value.
// This means it's either a mutable or fixed size arena string.
inline bool IsArena() const { return as_int() & kArenaBit; }
// Returns true if the current string is a fixed size arena allocated value.
inline bool IsFixedSizeArena() const {
return (as_int() & kMask) == kFixedSizeArena;
}
// Returns the contained string pointer.
inline std::string* Get() const {
return reinterpret_cast<std::string*>(as_int() & ~kMask);
}
// Returns true if the contained pointer is null, indicating some error.
// The Null value is only used during parsing for temporary values.
// A persisted ArenaStringPtr value is never null.
inline bool IsNull() { return ptr_ == nullptr; }
private:
static inline void assert_aligned(const void* p) {
GOOGLE_DCHECK_EQ(reinterpret_cast<uintptr_t>(p) & kMask, 0UL);
}
inline std::string* TagAs(Type type, std::string* p) {
GOOGLE_DCHECK(p != nullptr);
assert_aligned(p);
ptr_ = reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(p) | type);
return p;
}
uintptr_t as_int() const { return reinterpret_cast<uintptr_t>(ptr_); }
void* ptr_;
};
static_assert(std::is_trivial<TaggedStringPtr>::value,
"TaggedStringPtr must be trivial");
// This class encapsulates a pointer to a std::string with or without arena
// owned contents, tagged by the bottom bits of the string pointer. 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 string pointer is tagged to be either a default, externally owned value,
// a mutable heap allocated value, or an arena allocated value. The object uses
// a single global instance of an empty string that is used as the initial
// default value. Fields that have empty default values directly use this global
// default. Fields that have non empty default values are supported through
// lazily initialized default values managed by the LazyString class.
//
// Generated code and reflection code both ensure that ptr_ is never null.
// Because ArenaStringPtr is used in oneof unions, its constructor is a NOP and
// the field is always manually initialized via method calls.
//
// See TaggedStringPtr for more information about the types of string values
// being held, and the mutable and ownership invariants for each type.
struct PROTOBUF_EXPORT ArenaStringPtr {
ArenaStringPtr() = default;
constexpr ArenaStringPtr(ExplicitlyConstructedArenaString* default_value,
ConstantInitialized)
: tagged_ptr_(default_value) {}
// 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 InitDefault();
// Similar to `InitDefault` except that it allows the default value to be
// initialized to an externally owned string. This method is called from
// parsing code. `str` must not be null and outlive this instance.
inline void InitExternal(const std::string* str);
// Called from generated code / reflection runtime only. Resets the value of
// this instances to the heap allocated value in `str`. `str` must not be
// null. Invokes `arena->Own(str)` to transfer ownership into the arena if
// `arena` is not null, else, `str` will be owned by ArenaStringPtr. This
// function should only be used to initialize a ArenaStringPtr or on an
// instance known to not carry any heap allocated value.
inline void InitAllocated(std::string* str, Arena* arena);
void Set(ConstStringParam value, Arena* arena);
void Set(std::string&& value, Arena* arena);
void Set(const char* s, Arena* arena);
void Set(const char* s, size_t n, Arena* arena);
void SetBytes(ConstStringParam value, Arena* arena);
void SetBytes(std::string&& value, Arena* arena);
void SetBytes(const char* s, Arena* arena);
void SetBytes(const void* p, size_t n, Arena* arena);
template <typename RefWrappedType>
void Set(std::reference_wrapper<RefWrappedType> const_string_ref,
::google::protobuf::Arena* arena) {
Set(const_string_ref.get(), arena);
}
// Returns a mutable std::string reference.
// The version accepting a `LazyString` value is used in the generated code to
// initialize mutable copies for fields with a non-empty default where the
// default value is lazily initialized.
std::string* Mutable(Arena* arena);
std::string* Mutable(const LazyString& default_value, Arena* arena);
// Gets a mutable pointer with unspecified contents.
// This function is identical to Mutable(), except it is optimized for the
// case where the caller is not interested in the current contents. For
// example, if the current field is not mutable, it will re-initialize the
// value with an empty string rather than a (non-empty) default value.
// Likewise, if the current value is a fixed size arena string with contents,
// it will be initialized into an empty mutable arena string.
std::string* MutableNoCopy(Arena* arena);
// Basic accessors.
PROTOBUF_NDEBUG_INLINE const std::string& Get() const {
// Unconditionally mask away the tag.
return *tagged_ptr_.Get();
}
// Returns a pointer to the stored contents for this instance.
// This method is for internal debugging and tracking purposes only.
PROTOBUF_NDEBUG_INLINE const std::string* UnsafeGetPointer() const
PROTOBUF_RETURNS_NONNULL {
return tagged_ptr_.Get();
}
// 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 nullptr. The
// caller retains ownership. Clears this field back to the default state.
// Used to implement release_<field>() methods on generated classes.
PROTOBUF_NODISCARD std::string* Release();
// 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(std::string* value, Arena* arena);
// Frees storage (if not on an arena).
void Destroy();
// 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 != nullptr, 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);
// 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(ArenaStringPtr* rhs,
Arena* rhs_arena,
ArenaStringPtr* lhs,
Arena* lhs_arena);
// Internal setter used only at parse time to directly set a donated string
// value.
void UnsafeSetTaggedPointer(TaggedStringPtr 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;
// Returns true if this instances holds an immutable default value.
inline bool IsDefault() const { return tagged_ptr_.IsDefault(); }
private:
template <typename... Args>
inline std::string* NewString(Arena* arena, Args&&... args) {
if (arena == nullptr) {
auto* s = new std::string(std::forward<Args>(args)...);
return tagged_ptr_.SetAllocated(s);
} else {
auto* s = Arena::Create<std::string>(arena, std::forward<Args>(args)...);
return tagged_ptr_.SetMutableArena(s);
}
}
TaggedStringPtr tagged_ptr_;
bool IsFixedSizeArena() const { return false; }
// Swaps tagged pointer without debug hardening. This is to allow python
// protobuf to maintain pointer stability even in DEBUG builds.
inline PROTOBUF_NDEBUG_INLINE static void UnsafeShallowSwap(
ArenaStringPtr* rhs, ArenaStringPtr* lhs) {
std::swap(lhs->tagged_ptr_, rhs->tagged_ptr_);
}
friend class ::google::protobuf::internal::SwapFieldHelper;
friend class TcParser;
// Slow paths.
// MutableSlow requires that !IsString() || IsDefault
// Variadic to support 0 args for empty default and 1 arg for LazyString.
template <typename... Lazy>
std::string* MutableSlow(::google::protobuf::Arena* arena, const Lazy&... lazy_default);
friend class EpsCopyInputStream;
};
inline void ArenaStringPtr::InitDefault() {
tagged_ptr_ = TaggedStringPtr(&fixed_address_empty_string);
}
inline void ArenaStringPtr::InitExternal(const std::string* str) {
tagged_ptr_.SetDefault(str);
}
inline void ArenaStringPtr::InitAllocated(std::string* str, Arena* arena) {
if (arena != nullptr) {
tagged_ptr_.SetMutableArena(str);
arena->Own(str);
} else {
tagged_ptr_.SetAllocated(str);
}
}
inline void ArenaStringPtr::Set(const char* s, Arena* arena) {
Set(ConstStringParam{s}, arena);
}
inline void ArenaStringPtr::Set(const char* s, size_t n, Arena* arena) {
Set(ConstStringParam{s, n}, arena);
}
inline void ArenaStringPtr::SetBytes(ConstStringParam value, Arena* arena) {
Set(value, arena);
}
inline void ArenaStringPtr::SetBytes(std::string&& value, Arena* arena) {
Set(std::move(value), arena);
}
inline void ArenaStringPtr::SetBytes(const char* s, Arena* arena) {
Set(s, arena);
}
inline void ArenaStringPtr::SetBytes(const void* p, size_t n, Arena* arena) {
Set(ConstStringParam{static_cast<const char*>(p), n}, arena);
}
// Make sure rhs_arena allocated rhs, and lhs_arena allocated lhs.
inline PROTOBUF_NDEBUG_INLINE void ArenaStringPtr::InternalSwap( //
ArenaStringPtr* rhs, Arena* rhs_arena, //
ArenaStringPtr* lhs, Arena* lhs_arena) {
// Silence unused variable warnings in release buildls.
(void)rhs_arena;
(void)lhs_arena;
std::swap(lhs->tagged_ptr_, rhs->tagged_ptr_);
#ifdef PROTOBUF_FORCE_COPY_IN_SWAP
auto force_realloc = [](ArenaStringPtr* p, Arena* arena) {
if (p->IsDefault()) return;
std::string* old_value = p->tagged_ptr_.Get();
std::string* new_value =
p->IsFixedSizeArena()
? 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_.SetAllocated(new_value);
} else {
p->tagged_ptr_.SetMutableArena(new_value);
}
};
// Because, at this point, tagged_ptr_ has been swapped, arena should also be
// swapped.
force_realloc(lhs, rhs_arena);
force_realloc(rhs, lhs_arena);
#endif // PROTOBUF_FORCE_COPY_IN_SWAP
}
inline void ArenaStringPtr::ClearNonDefaultToEmpty() {
// Unconditionally mask away the tag.
tagged_ptr_.Get()->clear();
}
inline std::string* ArenaStringPtr::UnsafeMutablePointer() {
GOOGLE_DCHECK(tagged_ptr_.IsMutable());
GOOGLE_DCHECK(tagged_ptr_.Get() != nullptr);
return tagged_ptr_.Get();
}
} // namespace internal
} // namespace protobuf
} // namespace google
#include <google/protobuf/port_undef.inc>
#endif // GOOGLE_PROTOBUF_ARENASTRING_H__