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Diffstat (limited to 'third_party/abseil_cpp/absl/flags/internal/flag.h')
| -rw-r--r-- | third_party/abseil_cpp/absl/flags/internal/flag.h | 775 |
1 files changed, 775 insertions, 0 deletions
diff --git a/third_party/abseil_cpp/absl/flags/internal/flag.h b/third_party/abseil_cpp/absl/flags/internal/flag.h new file mode 100644 index 0000000000..370d8a02ef --- /dev/null +++ b/third_party/abseil_cpp/absl/flags/internal/flag.h @@ -0,0 +1,775 @@ +// +// 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. + +#ifndef ABSL_FLAGS_INTERNAL_FLAG_H_ +#define ABSL_FLAGS_INTERNAL_FLAG_H_ + +#include <stddef.h> +#include <stdint.h> + +#include <atomic> +#include <cstring> +#include <memory> +#include <new> +#include <string> +#include <type_traits> +#include <typeinfo> + +#include "absl/base/attributes.h" +#include "absl/base/call_once.h" +#include "absl/base/config.h" +#include "absl/base/optimization.h" +#include "absl/base/thread_annotations.h" +#include "absl/flags/commandlineflag.h" +#include "absl/flags/config.h" +#include "absl/flags/internal/commandlineflag.h" +#include "absl/flags/internal/registry.h" +#include "absl/flags/marshalling.h" +#include "absl/meta/type_traits.h" +#include "absl/strings/string_view.h" +#include "absl/synchronization/mutex.h" +#include "absl/utility/utility.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN + +/////////////////////////////////////////////////////////////////////////////// +// Forward declaration of absl::Flag<T> public API. +namespace flags_internal { +template <typename T> +class Flag; +} // namespace flags_internal + +#if defined(_MSC_VER) && !defined(__clang__) +template <typename T> +class Flag; +#else +template <typename T> +using Flag = flags_internal::Flag<T>; +#endif + +template <typename T> +ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag); + +template <typename T> +void SetFlag(absl::Flag<T>* flag, const T& v); + +template <typename T, typename V> +void SetFlag(absl::Flag<T>* flag, const V& v); + +template <typename U> +const CommandLineFlag& GetFlagReflectionHandle(const absl::Flag<U>& f); + +/////////////////////////////////////////////////////////////////////////////// +// Flag value type operations, eg., parsing, copying, etc. are provided +// by function specific to that type with a signature matching FlagOpFn. + +namespace flags_internal { + +enum class FlagOp { + kAlloc, + kDelete, + kCopy, + kCopyConstruct, + kSizeof, + kFastTypeId, + kRuntimeTypeId, + kParse, + kUnparse, + kValueOffset, +}; +using FlagOpFn = void* (*)(FlagOp, const void*, void*, void*); + +// Forward declaration for Flag value specific operations. +template <typename T> +void* FlagOps(FlagOp op, const void* v1, void* v2, void* v3); + +// Allocate aligned memory for a flag value. +inline void* Alloc(FlagOpFn op) { + return op(FlagOp::kAlloc, nullptr, nullptr, nullptr); +} +// Deletes memory interpreting obj as flag value type pointer. +inline void Delete(FlagOpFn op, void* obj) { + op(FlagOp::kDelete, nullptr, obj, nullptr); +} +// Copies src to dst interpreting as flag value type pointers. +inline void Copy(FlagOpFn op, const void* src, void* dst) { + op(FlagOp::kCopy, src, dst, nullptr); +} +// Construct a copy of flag value in a location pointed by dst +// based on src - pointer to the flag's value. +inline void CopyConstruct(FlagOpFn op, const void* src, void* dst) { + op(FlagOp::kCopyConstruct, src, dst, nullptr); +} +// Makes a copy of flag value pointed by obj. +inline void* Clone(FlagOpFn op, const void* obj) { + void* res = flags_internal::Alloc(op); + flags_internal::CopyConstruct(op, obj, res); + return res; +} +// Returns true if parsing of input text is successfull. +inline bool Parse(FlagOpFn op, absl::string_view text, void* dst, + std::string* error) { + return op(FlagOp::kParse, &text, dst, error) != nullptr; +} +// Returns string representing supplied value. +inline std::string Unparse(FlagOpFn op, const void* val) { + std::string result; + op(FlagOp::kUnparse, val, &result, nullptr); + return result; +} +// Returns size of flag value type. +inline size_t Sizeof(FlagOpFn op) { + // This sequence of casts reverses the sequence from + // `flags_internal::FlagOps()` + return static_cast<size_t>(reinterpret_cast<intptr_t>( + op(FlagOp::kSizeof, nullptr, nullptr, nullptr))); +} +// Returns fast type id coresponding to the value type. +inline FlagFastTypeId FastTypeId(FlagOpFn op) { + return reinterpret_cast<FlagFastTypeId>( + op(FlagOp::kFastTypeId, nullptr, nullptr, nullptr)); +} +// Returns fast type id coresponding to the value type. +inline const std::type_info* RuntimeTypeId(FlagOpFn op) { + return reinterpret_cast<const std::type_info*>( + op(FlagOp::kRuntimeTypeId, nullptr, nullptr, nullptr)); +} +// Returns offset of the field value_ from the field impl_ inside of +// absl::Flag<T> data. Given FlagImpl pointer p you can get the +// location of the corresponding value as: +// reinterpret_cast<char*>(p) + ValueOffset(). +inline ptrdiff_t ValueOffset(FlagOpFn op) { + // This sequence of casts reverses the sequence from + // `flags_internal::FlagOps()` + return static_cast<ptrdiff_t>(reinterpret_cast<intptr_t>( + op(FlagOp::kValueOffset, nullptr, nullptr, nullptr))); +} + +// Returns an address of RTTI's typeid(T). +template <typename T> +inline const std::type_info* GenRuntimeTypeId() { +#if defined(ABSL_FLAGS_INTERNAL_HAS_RTTI) + return &typeid(T); +#else + return nullptr; +#endif +} + +/////////////////////////////////////////////////////////////////////////////// +// Flag help auxiliary structs. + +// This is help argument for absl::Flag encapsulating the string literal pointer +// or pointer to function generating it as well as enum descriminating two +// cases. +using HelpGenFunc = std::string (*)(); + +template <size_t N> +struct FixedCharArray { + char value[N]; + + template <size_t... I> + static constexpr FixedCharArray<N> FromLiteralString( + absl::string_view str, absl::index_sequence<I...>) { + return (void)str, FixedCharArray<N>({{str[I]..., '\0'}}); + } +}; + +template <typename Gen, size_t N = Gen::Value().size()> +constexpr FixedCharArray<N + 1> HelpStringAsArray(int) { + return FixedCharArray<N + 1>::FromLiteralString( + Gen::Value(), absl::make_index_sequence<N>{}); +} + +template <typename Gen> +constexpr std::false_type HelpStringAsArray(char) { + return std::false_type{}; +} + +union FlagHelpMsg { + constexpr explicit FlagHelpMsg(const char* help_msg) : literal(help_msg) {} + constexpr explicit FlagHelpMsg(HelpGenFunc help_gen) : gen_func(help_gen) {} + + const char* literal; + HelpGenFunc gen_func; +}; + +enum class FlagHelpKind : uint8_t { kLiteral = 0, kGenFunc = 1 }; + +struct FlagHelpArg { + FlagHelpMsg source; + FlagHelpKind kind; +}; + +extern const char kStrippedFlagHelp[]; + +// These two HelpArg overloads allows us to select at compile time one of two +// way to pass Help argument to absl::Flag. We'll be passing +// AbslFlagHelpGenFor##name as Gen and integer 0 as a single argument to prefer +// first overload if possible. If help message is evaluatable on constexpr +// context We'll be able to make FixedCharArray out of it and we'll choose first +// overload. In this case the help message expression is immediately evaluated +// and is used to construct the absl::Flag. No additionl code is generated by +// ABSL_FLAG Otherwise SFINAE kicks in and first overload is dropped from the +// consideration, in which case the second overload will be used. The second +// overload does not attempt to evaluate the help message expression +// immediately and instead delays the evaluation by returing the function +// pointer (&T::NonConst) genering the help message when necessary. This is +// evaluatable in constexpr context, but the cost is an extra function being +// generated in the ABSL_FLAG code. +template <typename Gen, size_t N> +constexpr FlagHelpArg HelpArg(const FixedCharArray<N>& value) { + return {FlagHelpMsg(value.value), FlagHelpKind::kLiteral}; +} + +template <typename Gen> +constexpr FlagHelpArg HelpArg(std::false_type) { + return {FlagHelpMsg(&Gen::NonConst), FlagHelpKind::kGenFunc}; +} + +/////////////////////////////////////////////////////////////////////////////// +// Flag default value auxiliary structs. + +// Signature for the function generating the initial flag value (usually +// based on default value supplied in flag's definition) +using FlagDfltGenFunc = void (*)(void*); + +union FlagDefaultSrc { + constexpr explicit FlagDefaultSrc(FlagDfltGenFunc gen_func_arg) + : gen_func(gen_func_arg) {} + +#define ABSL_FLAGS_INTERNAL_DFLT_FOR_TYPE(T, name) \ + T name##_value; \ + constexpr explicit FlagDefaultSrc(T value) : name##_value(value) {} // NOLINT + ABSL_FLAGS_INTERNAL_BUILTIN_TYPES(ABSL_FLAGS_INTERNAL_DFLT_FOR_TYPE) +#undef ABSL_FLAGS_INTERNAL_DFLT_FOR_TYPE + + void* dynamic_value; + FlagDfltGenFunc gen_func; +}; + +enum class FlagDefaultKind : uint8_t { + kDynamicValue = 0, + kGenFunc = 1, + kOneWord = 2 // for default values UP to one word in size +}; + +struct FlagDefaultArg { + FlagDefaultSrc source; + FlagDefaultKind kind; +}; + +// This struct and corresponding overload to InitDefaultValue are used to +// facilitate usage of {} as default value in ABSL_FLAG macro. +// TODO(rogeeff): Fix handling types with explicit constructors. +struct EmptyBraces {}; + +template <typename T> +constexpr T InitDefaultValue(T t) { + return t; +} + +template <typename T> +constexpr T InitDefaultValue(EmptyBraces) { + return T{}; +} + +template <typename ValueT, typename GenT, + typename std::enable_if<std::is_integral<ValueT>::value, int>::type = + (GenT{}, 0)> +constexpr FlagDefaultArg DefaultArg(int) { + return {FlagDefaultSrc(GenT{}.value), FlagDefaultKind::kOneWord}; +} + +template <typename ValueT, typename GenT> +constexpr FlagDefaultArg DefaultArg(char) { + return {FlagDefaultSrc(&GenT::Gen), FlagDefaultKind::kGenFunc}; +} + +/////////////////////////////////////////////////////////////////////////////// +// Flag current value auxiliary structs. + +constexpr int64_t UninitializedFlagValue() { return 0xababababababababll; } + +template <typename T> +using FlagUseOneWordStorage = std::integral_constant< + bool, absl::type_traits_internal::is_trivially_copyable<T>::value && + (sizeof(T) <= 8)>; + +#if defined(ABSL_FLAGS_INTERNAL_ATOMIC_DOUBLE_WORD) +// Clang does not always produce cmpxchg16b instruction when alignment of a 16 +// bytes type is not 16. +struct alignas(16) AlignedTwoWords { + int64_t first; + int64_t second; + + bool IsInitialized() const { + return first != flags_internal::UninitializedFlagValue(); + } +}; + +template <typename T> +using FlagUseTwoWordsStorage = std::integral_constant< + bool, absl::type_traits_internal::is_trivially_copyable<T>::value && + (sizeof(T) > 8) && (sizeof(T) <= 16)>; +#else +// This is actually unused and only here to avoid ifdefs in other palces. +struct AlignedTwoWords { + constexpr AlignedTwoWords() noexcept : dummy() {} + constexpr AlignedTwoWords(int64_t, int64_t) noexcept : dummy() {} + char dummy; + + bool IsInitialized() const { + std::abort(); + return true; + } +}; + +// This trait should be type dependent, otherwise SFINAE below will fail +template <typename T> +using FlagUseTwoWordsStorage = + std::integral_constant<bool, sizeof(T) != sizeof(T)>; +#endif + +template <typename T> +using FlagUseBufferStorage = + std::integral_constant<bool, !FlagUseOneWordStorage<T>::value && + !FlagUseTwoWordsStorage<T>::value>; + +enum class FlagValueStorageKind : uint8_t { + kAlignedBuffer = 0, + kOneWordAtomic = 1, + kTwoWordsAtomic = 2 +}; + +template <typename T> +static constexpr FlagValueStorageKind StorageKind() { + return FlagUseBufferStorage<T>::value + ? FlagValueStorageKind::kAlignedBuffer + : FlagUseOneWordStorage<T>::value + ? FlagValueStorageKind::kOneWordAtomic + : FlagValueStorageKind::kTwoWordsAtomic; +} + +struct FlagOneWordValue { + constexpr FlagOneWordValue() : value(UninitializedFlagValue()) {} + + std::atomic<int64_t> value; +}; + +struct FlagTwoWordsValue { + constexpr FlagTwoWordsValue() + : value(AlignedTwoWords{UninitializedFlagValue(), 0}) {} + + std::atomic<AlignedTwoWords> value; +}; + +template <typename T, + FlagValueStorageKind Kind = flags_internal::StorageKind<T>()> +struct FlagValue; + +template <typename T> +struct FlagValue<T, FlagValueStorageKind::kAlignedBuffer> { + bool Get(T&) const { return false; } + + alignas(T) char value[sizeof(T)]; +}; + +template <typename T> +struct FlagValue<T, FlagValueStorageKind::kOneWordAtomic> : FlagOneWordValue { + bool Get(T& dst) const { + int64_t one_word_val = value.load(std::memory_order_acquire); + if (ABSL_PREDICT_FALSE(one_word_val == UninitializedFlagValue())) { + return false; + } + std::memcpy(&dst, static_cast<const void*>(&one_word_val), sizeof(T)); + return true; + } +}; + +template <typename T> +struct FlagValue<T, FlagValueStorageKind::kTwoWordsAtomic> : FlagTwoWordsValue { + bool Get(T& dst) const { + AlignedTwoWords two_words_val = value.load(std::memory_order_acquire); + if (ABSL_PREDICT_FALSE(!two_words_val.IsInitialized())) { + return false; + } + std::memcpy(&dst, static_cast<const void*>(&two_words_val), sizeof(T)); + return true; + } +}; + +/////////////////////////////////////////////////////////////////////////////// +// Flag callback auxiliary structs. + +// Signature for the mutation callback used by watched Flags +// The callback is noexcept. +// TODO(rogeeff): add noexcept after C++17 support is added. +using FlagCallbackFunc = void (*)(); + +struct FlagCallback { + FlagCallbackFunc func; + absl::Mutex guard; // Guard for concurrent callback invocations. +}; + +/////////////////////////////////////////////////////////////////////////////// +// Flag implementation, which does not depend on flag value type. +// The class encapsulates the Flag's data and access to it. + +struct DynValueDeleter { + explicit DynValueDeleter(FlagOpFn op_arg = nullptr); + void operator()(void* ptr) const; + + FlagOpFn op; +}; + +class FlagState; + +class FlagImpl final : public CommandLineFlag { + public: + constexpr FlagImpl(const char* name, const char* filename, FlagOpFn op, + FlagHelpArg help, FlagValueStorageKind value_kind, + FlagDefaultArg default_arg) + : name_(name), + filename_(filename), + op_(op), + help_(help.source), + help_source_kind_(static_cast<uint8_t>(help.kind)), + value_storage_kind_(static_cast<uint8_t>(value_kind)), + def_kind_(static_cast<uint8_t>(default_arg.kind)), + modified_(false), + on_command_line_(false), + counter_(0), + callback_(nullptr), + default_value_(default_arg.source), + data_guard_{} {} + + // Constant access methods + void Read(void* dst) const override ABSL_LOCKS_EXCLUDED(*DataGuard()); + + // Mutating access methods + void Write(const void* src) ABSL_LOCKS_EXCLUDED(*DataGuard()); + + // Interfaces to operate on callbacks. + void SetCallback(const FlagCallbackFunc mutation_callback) + ABSL_LOCKS_EXCLUDED(*DataGuard()); + void InvokeCallback() const ABSL_EXCLUSIVE_LOCKS_REQUIRED(*DataGuard()); + + // Used in read/write operations to validate source/target has correct type. + // For example if flag is declared as absl::Flag<int> FLAGS_foo, a call to + // absl::GetFlag(FLAGS_foo) validates that the type of FLAGS_foo is indeed + // int. To do that we pass the "assumed" type id (which is deduced from type + // int) as an argument `type_id`, which is in turn is validated against the + // type id stored in flag object by flag definition statement. + void AssertValidType(FlagFastTypeId type_id, + const std::type_info* (*gen_rtti)()) const; + + private: + template <typename T> + friend class Flag; + friend class FlagState; + + // Ensures that `data_guard_` is initialized and returns it. + absl::Mutex* DataGuard() const + ABSL_LOCK_RETURNED(reinterpret_cast<absl::Mutex*>(data_guard_)); + // Returns heap allocated value of type T initialized with default value. + std::unique_ptr<void, DynValueDeleter> MakeInitValue() const + ABSL_EXCLUSIVE_LOCKS_REQUIRED(*DataGuard()); + // Flag initialization called via absl::call_once. + void Init(); + + // Offset value access methods. One per storage kind. These methods to not + // respect const correctness, so be very carefull using them. + + // This is a shared helper routine which encapsulates most of the magic. Since + // it is only used inside the three routines below, which are defined in + // flag.cc, we can define it in that file as well. + template <typename StorageT> + StorageT* OffsetValue() const; + // This is an accessor for a value stored in an aligned buffer storage. + // Returns a mutable pointer to the start of a buffer. + void* AlignedBufferValue() const; + // This is an accessor for a value stored as one word atomic. Returns a + // mutable reference to an atomic value. + std::atomic<int64_t>& OneWordValue() const; + // This is an accessor for a value stored as two words atomic. Returns a + // mutable reference to an atomic value. + std::atomic<AlignedTwoWords>& TwoWordsValue() const; + + // Attempts to parse supplied `value` string. If parsing is successful, + // returns new value. Otherwise returns nullptr. + std::unique_ptr<void, DynValueDeleter> TryParse(absl::string_view value, + std::string& err) const + ABSL_EXCLUSIVE_LOCKS_REQUIRED(*DataGuard()); + // Stores the flag value based on the pointer to the source. + void StoreValue(const void* src) ABSL_EXCLUSIVE_LOCKS_REQUIRED(*DataGuard()); + + FlagHelpKind HelpSourceKind() const { + return static_cast<FlagHelpKind>(help_source_kind_); + } + FlagValueStorageKind ValueStorageKind() const { + return static_cast<FlagValueStorageKind>(value_storage_kind_); + } + FlagDefaultKind DefaultKind() const + ABSL_EXCLUSIVE_LOCKS_REQUIRED(*DataGuard()) { + return static_cast<FlagDefaultKind>(def_kind_); + } + + // CommandLineFlag interface implementation + absl::string_view Name() const override; + std::string Filename() const override; + std::string Help() const override; + FlagFastTypeId TypeId() const override; + bool IsSpecifiedOnCommandLine() const override + ABSL_LOCKS_EXCLUDED(*DataGuard()); + std::string DefaultValue() const override ABSL_LOCKS_EXCLUDED(*DataGuard()); + std::string CurrentValue() const override ABSL_LOCKS_EXCLUDED(*DataGuard()); + bool ValidateInputValue(absl::string_view value) const override + ABSL_LOCKS_EXCLUDED(*DataGuard()); + void CheckDefaultValueParsingRoundtrip() const override + ABSL_LOCKS_EXCLUDED(*DataGuard()); + + // Interfaces to save and restore flags to/from persistent state. + // Returns current flag state or nullptr if flag does not support + // saving and restoring a state. + std::unique_ptr<FlagStateInterface> SaveState() override + ABSL_LOCKS_EXCLUDED(*DataGuard()); + + // Restores the flag state to the supplied state object. If there is + // nothing to restore returns false. Otherwise returns true. + bool RestoreState(const FlagState& flag_state) + ABSL_LOCKS_EXCLUDED(*DataGuard()); + + bool ParseFrom(absl::string_view value, FlagSettingMode set_mode, + ValueSource source, std::string& error) override + ABSL_LOCKS_EXCLUDED(*DataGuard()); + + // Immutable flag's state. + + // Flags name passed to ABSL_FLAG as second arg. + const char* const name_; + // The file name where ABSL_FLAG resides. + const char* const filename_; + // Type-specific operations "vtable". + const FlagOpFn op_; + // Help message literal or function to generate it. + const FlagHelpMsg help_; + // Indicates if help message was supplied as literal or generator func. + const uint8_t help_source_kind_ : 1; + // Kind of storage this flag is using for the flag's value. + const uint8_t value_storage_kind_ : 2; + + uint8_t : 0; // The bytes containing the const bitfields must not be + // shared with bytes containing the mutable bitfields. + + // Mutable flag's state (guarded by `data_guard_`). + + // def_kind_ is not guard by DataGuard() since it is accessed in Init without + // locks. + uint8_t def_kind_ : 2; + // Has this flag's value been modified? + bool modified_ : 1 ABSL_GUARDED_BY(*DataGuard()); + // Has this flag been specified on command line. + bool on_command_line_ : 1 ABSL_GUARDED_BY(*DataGuard()); + + // Unique tag for absl::call_once call to initialize this flag. + absl::once_flag init_control_; + + // Mutation counter + int64_t counter_ ABSL_GUARDED_BY(*DataGuard()); + // Optional flag's callback and absl::Mutex to guard the invocations. + FlagCallback* callback_ ABSL_GUARDED_BY(*DataGuard()); + // Either a pointer to the function generating the default value based on the + // value specified in ABSL_FLAG or pointer to the dynamically set default + // value via SetCommandLineOptionWithMode. def_kind_ is used to distinguish + // these two cases. + FlagDefaultSrc default_value_; + + // This is reserved space for an absl::Mutex to guard flag data. It will be + // initialized in FlagImpl::Init via placement new. + // We can't use "absl::Mutex data_guard_", since this class is not literal. + // We do not want to use "absl::Mutex* data_guard_", since this would require + // heap allocation during initialization, which is both slows program startup + // and can fail. Using reserved space + placement new allows us to avoid both + // problems. + alignas(absl::Mutex) mutable char data_guard_[sizeof(absl::Mutex)]; +}; + +/////////////////////////////////////////////////////////////////////////////// +// The Flag object parameterized by the flag's value type. This class implements +// flag reflection handle interface. + +template <typename T> +class Flag { + public: + constexpr Flag(const char* name, const char* filename, FlagHelpArg help, + const FlagDefaultArg default_arg) + : impl_(name, filename, &FlagOps<T>, help, + flags_internal::StorageKind<T>(), default_arg), + value_() {} + + // CommandLineFlag interface + absl::string_view Name() const { return impl_.Name(); } + std::string Filename() const { return impl_.Filename(); } + std::string Help() const { return impl_.Help(); } + // Do not use. To be removed. + bool IsSpecifiedOnCommandLine() const { + return impl_.IsSpecifiedOnCommandLine(); + } + std::string DefaultValue() const { return impl_.DefaultValue(); } + std::string CurrentValue() const { return impl_.CurrentValue(); } + + private: + template <typename, bool> + friend class FlagRegistrar; + friend class FlagImplPeer; + + T Get() const { + // See implementation notes in CommandLineFlag::Get(). + union U { + T value; + U() {} + ~U() { value.~T(); } + }; + U u; + +#if !defined(NDEBUG) + impl_.AssertValidType(base_internal::FastTypeId<T>(), &GenRuntimeTypeId<T>); +#endif + + if (!value_.Get(u.value)) impl_.Read(&u.value); + return std::move(u.value); + } + void Set(const T& v) { + impl_.AssertValidType(base_internal::FastTypeId<T>(), &GenRuntimeTypeId<T>); + impl_.Write(&v); + } + + // Access to the reflection. + const CommandLineFlag& Reflect() const { return impl_; } + + // Flag's data + // The implementation depends on value_ field to be placed exactly after the + // impl_ field, so that impl_ can figure out the offset to the value and + // access it. + FlagImpl impl_; + FlagValue<T> value_; +}; + +/////////////////////////////////////////////////////////////////////////////// +// Trampoline for friend access + +class FlagImplPeer { + public: + template <typename T, typename FlagType> + static T InvokeGet(const FlagType& flag) { + return flag.Get(); + } + template <typename FlagType, typename T> + static void InvokeSet(FlagType& flag, const T& v) { + flag.Set(v); + } + template <typename FlagType> + static const CommandLineFlag& InvokeReflect(const FlagType& f) { + return f.Reflect(); + } +}; + +/////////////////////////////////////////////////////////////////////////////// +// Implementation of Flag value specific operations routine. +template <typename T> +void* FlagOps(FlagOp op, const void* v1, void* v2, void* v3) { + switch (op) { + case FlagOp::kAlloc: { + std::allocator<T> alloc; + return std::allocator_traits<std::allocator<T>>::allocate(alloc, 1); + } + case FlagOp::kDelete: { + T* p = static_cast<T*>(v2); + p->~T(); + std::allocator<T> alloc; + std::allocator_traits<std::allocator<T>>::deallocate(alloc, p, 1); + return nullptr; + } + case FlagOp::kCopy: + *static_cast<T*>(v2) = *static_cast<const T*>(v1); + return nullptr; + case FlagOp::kCopyConstruct: + new (v2) T(*static_cast<const T*>(v1)); + return nullptr; + case FlagOp::kSizeof: + return reinterpret_cast<void*>(static_cast<uintptr_t>(sizeof(T))); + case FlagOp::kFastTypeId: + return const_cast<void*>(base_internal::FastTypeId<T>()); + case FlagOp::kRuntimeTypeId: + return const_cast<std::type_info*>(GenRuntimeTypeId<T>()); + case FlagOp::kParse: { + // Initialize the temporary instance of type T based on current value in + // destination (which is going to be flag's default value). + T temp(*static_cast<T*>(v2)); + if (!absl::ParseFlag<T>(*static_cast<const absl::string_view*>(v1), &temp, + static_cast<std::string*>(v3))) { + return nullptr; + } + *static_cast<T*>(v2) = std::move(temp); + return v2; + } + case FlagOp::kUnparse: + *static_cast<std::string*>(v2) = + absl::UnparseFlag<T>(*static_cast<const T*>(v1)); + return nullptr; + case FlagOp::kValueOffset: { + // Round sizeof(FlagImp) to a multiple of alignof(FlagValue<T>) to get the + // offset of the data. + ptrdiff_t round_to = alignof(FlagValue<T>); + ptrdiff_t offset = + (sizeof(FlagImpl) + round_to - 1) / round_to * round_to; + return reinterpret_cast<void*>(offset); + } + } + return nullptr; +} + +/////////////////////////////////////////////////////////////////////////////// +// This class facilitates Flag object registration and tail expression-based +// flag definition, for example: +// ABSL_FLAG(int, foo, 42, "Foo help").OnUpdate(NotifyFooWatcher); +struct FlagRegistrarEmpty {}; +template <typename T, bool do_register> +class FlagRegistrar { + public: + explicit FlagRegistrar(Flag<T>& flag) : flag_(flag) { + if (do_register) flags_internal::RegisterCommandLineFlag(flag_.impl_); + } + + FlagRegistrar OnUpdate(FlagCallbackFunc cb) && { + flag_.impl_.SetCallback(cb); + return *this; + } + + // Make the registrar "die" gracefully as an empty struct on a line where + // registration happens. Registrar objects are intended to live only as + // temporary. + operator FlagRegistrarEmpty() const { return {}; } // NOLINT + + private: + Flag<T>& flag_; // Flag being registered (not owned). +}; + +} // namespace flags_internal +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_FLAGS_INTERNAL_FLAG_H_ |