diff options
Diffstat (limited to 'absl/flags/internal/flag.h')
| -rw-r--r-- | absl/flags/internal/flag.h | 794 |
1 files changed, 449 insertions, 345 deletions
diff --git a/absl/flags/internal/flag.h b/absl/flags/internal/flag.h index 35a148cf..370d8a02 100644 --- a/absl/flags/internal/flag.h +++ b/absl/flags/internal/flag.h @@ -16,94 +16,93 @@ #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/memory/memory.h" -#include "absl/strings/str_cat.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, - kClone, kCopy, kCopyConstruct, kSizeof, - kStaticTypeId, + kFastTypeId, + kRuntimeTypeId, kParse, kUnparse, + kValueOffset, }; using FlagOpFn = void* (*)(FlagOp, const void*, void*, void*); -// Flag value specific operations routine. +// Forward declaration for Flag value specific operations. template <typename T> -void* FlagOps(FlagOp op, const void* v1, void* v2, void* v3) { - switch (op) { - case FlagOp::kDelete: - delete static_cast<const T*>(v1); - return nullptr; - case FlagOp::kClone: - return new T(*static_cast<const T*>(v1)); - 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*>(sizeof(T)); - case FlagOp::kStaticTypeId: - return reinterpret_cast<void*>(&FlagStaticTypeIdGen<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; - default: - return nullptr; - } -} +void* FlagOps(FlagOp op, const void* v1, void* v2, void* v3); -// Deletes memory interpreting obj as flag value type pointer. -inline void Delete(FlagOpFn op, const void* obj) { - op(FlagOp::kDelete, obj, nullptr, nullptr); +// Allocate aligned memory for a flag value. +inline void* Alloc(FlagOpFn op) { + return op(FlagOp::kAlloc, nullptr, nullptr, nullptr); } -// Makes a copy of flag value pointed by obj. -inline void* Clone(FlagOpFn op, const void* obj) { - return op(FlagOp::kClone, obj, 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) { @@ -114,6 +113,12 @@ inline void Copy(FlagOpFn op, const void* src, void* dst) { 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) { @@ -132,41 +137,36 @@ inline size_t Sizeof(FlagOpFn op) { return static_cast<size_t>(reinterpret_cast<intptr_t>( op(FlagOp::kSizeof, nullptr, nullptr, nullptr))); } -// Returns static type id coresponding to the value type. -inline FlagStaticTypeId StaticTypeId(FlagOpFn op) { - return reinterpret_cast<FlagStaticTypeId>( - op(FlagOp::kStaticTypeId, 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))); } -/////////////////////////////////////////////////////////////////////////////// -// Persistent state of the flag data. - +// Returns an address of RTTI's typeid(T). template <typename T> -class FlagState : public flags_internal::FlagStateInterface { - public: - FlagState(Flag<T>* flag, T&& cur, bool modified, bool on_command_line, - int64_t counter) - : flag_(flag), - cur_value_(std::move(cur)), - modified_(modified), - on_command_line_(on_command_line), - counter_(counter) {} - - ~FlagState() override = default; - - private: - friend class Flag<T>; - - // Restores the flag to the saved state. - void Restore() const override; - - // Flag and saved flag data. - Flag<T>* flag_; - T cur_value_; - bool modified_; - bool on_command_line_; - int64_t counter_; -}; +inline const std::type_info* GenRuntimeTypeId() { +#if defined(ABSL_FLAGS_INTERNAL_HAS_RTTI) + return &typeid(T); +#else + return nullptr; +#endif +} /////////////////////////////////////////////////////////////////////////////// // Flag help auxiliary structs. @@ -176,6 +176,28 @@ class FlagState : public flags_internal::FlagStateInterface { // 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) {} @@ -193,40 +215,28 @@ struct FlagHelpArg { extern const char kStrippedFlagHelp[]; -// HelpConstexprWrap is used by struct AbslFlagHelpGenFor##name generated by -// ABSL_FLAG macro. It is only used to silence the compiler in the case where -// help message expression is not constexpr and does not have type const char*. -// If help message expression is indeed constexpr const char* HelpConstexprWrap -// is just a trivial identity function. -template <typename T> -const char* HelpConstexprWrap(const T&) { - return nullptr; -} -constexpr const char* HelpConstexprWrap(const char* p) { return p; } -constexpr const char* HelpConstexprWrap(char* p) { return p; } - // 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 T and integer 0 as a single argument to prefer -// first overload if possible. If T::Const is evaluatable on constexpr -// context (see non template int parameter below) 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 +// 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 T, int = (T::Const(), 1)> -constexpr FlagHelpArg HelpArg(int) { - return {FlagHelpMsg(T::Const()), FlagHelpKind::kLiteral}; +template <typename Gen, size_t N> +constexpr FlagHelpArg HelpArg(const FixedCharArray<N>& value) { + return {FlagHelpMsg(value.value), FlagHelpKind::kLiteral}; } -template <typename T> -constexpr FlagHelpArg HelpArg(char) { - return {FlagHelpMsg(&T::NonConst), FlagHelpKind::kGenFunc}; +template <typename Gen> +constexpr FlagHelpArg HelpArg(std::false_type) { + return {FlagHelpMsg(&Gen::NonConst), FlagHelpKind::kGenFunc}; } /////////////////////////////////////////////////////////////////////////////// @@ -234,110 +244,171 @@ constexpr FlagHelpArg HelpArg(char) { // Signature for the function generating the initial flag value (usually // based on default value supplied in flag's definition) -using FlagDfltGenFunc = void* (*)(); +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 }; +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. -// The minimum atomic size we believe to generate lock free code, i.e. all -// trivially copyable types not bigger this size generate lock free code. -static constexpr int kMinLockFreeAtomicSize = 8; - -// The same as kMinLockFreeAtomicSize but maximum atomic size. As double words -// might use two registers, we want to dispatch the logic for them. -#if defined(ABSL_FLAGS_INTERNAL_ATOMIC_DOUBLE_WORD) -static constexpr int kMaxLockFreeAtomicSize = 16; -#else -static constexpr int kMaxLockFreeAtomicSize = 8; -#endif +constexpr int64_t UninitializedFlagValue() { return 0xababababababababll; } -// We can use atomic in cases when it fits in the register, trivially copyable -// in order to make memcpy operations. template <typename T> -struct IsAtomicFlagTypeTrait { - static constexpr bool value = - (sizeof(T) <= kMaxLockFreeAtomicSize && - type_traits_internal::is_trivially_copyable<T>::value); -}; +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) FlagsInternalTwoWordsType { +struct alignas(16) AlignedTwoWords { int64_t first; int64_t second; + + bool IsInitialized() const { + return first != flags_internal::UninitializedFlagValue(); + } }; -constexpr bool operator==(const FlagsInternalTwoWordsType& that, - const FlagsInternalTwoWordsType& other) { - return that.first == other.first && that.second == other.second; -} -constexpr bool operator!=(const FlagsInternalTwoWordsType& that, - const FlagsInternalTwoWordsType& other) { - return !(that == other); +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; } -constexpr int64_t SmallAtomicInit() { return 0xababababababababll; } +struct FlagOneWordValue { + constexpr FlagOneWordValue() : value(UninitializedFlagValue()) {} -template <typename T, typename S = void> -struct BestAtomicType { - using type = int64_t; - static constexpr int64_t AtomicInit() { return SmallAtomicInit(); } + 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 BestAtomicType< - T, typename std::enable_if<(kMinLockFreeAtomicSize < sizeof(T) && - sizeof(T) <= kMaxLockFreeAtomicSize), - void>::type> { - using type = FlagsInternalTwoWordsType; - static constexpr FlagsInternalTwoWordsType AtomicInit() { - return {SmallAtomicInit(), SmallAtomicInit()}; - } +struct FlagValue<T, FlagValueStorageKind::kAlignedBuffer> { + bool Get(T&) const { return false; } + + alignas(T) char value[sizeof(T)]; }; -struct FlagValue { - // Heap allocated value. - void* dynamic = nullptr; - // For some types, a copy of the current value is kept in an atomically - // accessible field. - union Atomics { - // Using small atomic for small types. - std::atomic<int64_t> small_atomic; - template <typename T, - typename K = typename std::enable_if< - (sizeof(T) <= kMinLockFreeAtomicSize), void>::type> - int64_t load() const { - return small_atomic.load(std::memory_order_acquire); +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; + } +}; -#if defined(ABSL_FLAGS_INTERNAL_ATOMIC_DOUBLE_WORD) - // Using big atomics for big types. - std::atomic<FlagsInternalTwoWordsType> big_atomic; - template <typename T, typename K = typename std::enable_if< - (kMinLockFreeAtomicSize < sizeof(T) && - sizeof(T) <= kMaxLockFreeAtomicSize), - void>::type> - FlagsInternalTwoWordsType load() const { - return big_atomic.load(std::memory_order_acquire); +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; } - constexpr Atomics() - : big_atomic{FlagsInternalTwoWordsType{SmallAtomicInit(), - SmallAtomicInit()}} {} -#else - constexpr Atomics() : small_atomic{SmallAtomicInit()} {} -#endif - }; - Atomics atomics{}; + std::memcpy(&dst, static_cast<const void*>(&two_words_val), sizeof(T)); + return true; + } }; /////////////////////////////////////////////////////////////////////////////// @@ -358,116 +429,89 @@ struct FlagCallback { // The class encapsulates the Flag's data and access to it. struct DynValueDeleter { - explicit DynValueDeleter(FlagOpFn op_arg = nullptr) : op(op_arg) {} - void operator()(void* ptr) const { - if (op != nullptr) Delete(op, ptr); - } + explicit DynValueDeleter(FlagOpFn op_arg = nullptr); + void operator()(void* ptr) const; FlagOpFn op; }; -class FlagImpl { +class FlagState; + +class FlagImpl final : public CommandLineFlag { public: constexpr FlagImpl(const char* name, const char* filename, FlagOpFn op, - FlagHelpArg help, FlagDfltGenFunc default_value_gen) + 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)), - def_kind_(static_cast<uint8_t>(FlagDefaultKind::kGenFunc)), + 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_value_gen), + default_value_(default_arg.source), data_guard_{} {} // Constant access methods - absl::string_view Name() const; - std::string Filename() const; - std::string Help() const; - bool IsModified() const ABSL_LOCKS_EXCLUDED(*DataGuard()); - bool IsSpecifiedOnCommandLine() const ABSL_LOCKS_EXCLUDED(*DataGuard()); - std::string DefaultValue() const ABSL_LOCKS_EXCLUDED(*DataGuard()); - std::string CurrentValue() const ABSL_LOCKS_EXCLUDED(*DataGuard()); - void Read(void* dst) const ABSL_LOCKS_EXCLUDED(*DataGuard()); - - template <typename T, typename std::enable_if< - !IsAtomicFlagTypeTrait<T>::value, int>::type = 0> - void Get(T* dst) const { - AssertValidType(&flags_internal::FlagStaticTypeIdGen<T>); - Read(dst); - } - // Overload for `GetFlag()` for types that support lock-free reads. - template <typename T, typename std::enable_if<IsAtomicFlagTypeTrait<T>::value, - int>::type = 0> - void Get(T* dst) const { - // For flags of types which can be accessed "atomically" we want to avoid - // slowing down flag value access due to type validation. That's why - // this validation is hidden behind !NDEBUG -#ifndef NDEBUG - AssertValidType(&flags_internal::FlagStaticTypeIdGen<T>); -#endif - using U = flags_internal::BestAtomicType<T>; - typename U::type r = value_.atomics.template load<T>(); - if (r != U::AtomicInit()) { - std::memcpy(static_cast<void*>(dst), &r, sizeof(T)); - } else { - Read(dst); - } - } - template <typename T> - void Set(const T& src) { - AssertValidType(&flags_internal::FlagStaticTypeIdGen<T>); - Write(&src); - } + void Read(void* dst) const override ABSL_LOCKS_EXCLUDED(*DataGuard()); // Mutating access methods void Write(const void* src) ABSL_LOCKS_EXCLUDED(*DataGuard()); - bool SetFromString(absl::string_view value, FlagSettingMode set_mode, - ValueSource source, std::string* err) - ABSL_LOCKS_EXCLUDED(*DataGuard()); - // If possible, updates copy of the Flag's value that is stored in an - // atomic word. - void StoreAtomic() ABSL_EXCLUSIVE_LOCKS_REQUIRED(*DataGuard()); // Interfaces to operate on callbacks. void SetCallback(const FlagCallbackFunc mutation_callback) ABSL_LOCKS_EXCLUDED(*DataGuard()); void InvokeCallback() const ABSL_EXCLUSIVE_LOCKS_REQUIRED(*DataGuard()); - // Interfaces to save/restore mutable flag data - template <typename T> - std::unique_ptr<FlagStateInterface> SaveState(Flag<T>* flag) const - ABSL_LOCKS_EXCLUDED(*DataGuard()) { - T&& cur_value = flag->Get(); - absl::MutexLock l(DataGuard()); - - return absl::make_unique<FlagState<T>>( - flag, std::move(cur_value), modified_, on_command_line_, counter_); - } - bool RestoreState(const void* value, bool modified, bool on_command_line, - int64_t counter) ABSL_LOCKS_EXCLUDED(*DataGuard()); - - // Value validation interfaces. - void CheckDefaultValueParsingRoundtrip() const - ABSL_LOCKS_EXCLUDED(*DataGuard()); - bool ValidateInputValue(absl::string_view value) const - ABSL_LOCKS_EXCLUDED(*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((absl::Mutex*)&data_guard_); + 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(); - // Attempts to parse supplied `value` std::string. If parsing is successful, + + // 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 + 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()); @@ -475,17 +519,42 @@ class FlagImpl { 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_); } - // 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 `op`, which is in turn is validated against the type id - // stored in flag object by flag definition statement. - void AssertValidType(FlagStaticTypeId type_id) const; + + // 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. @@ -499,29 +568,25 @@ class FlagImpl { 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; - // ------------------------------------------------------------------------ - // The bytes containing the const bitfields must not be shared with bytes - // containing the mutable bitfields. - // ------------------------------------------------------------------------ - - // Unique tag for absl::call_once call to initialize this flag. - // - // The placement of this variable between the immutable and mutable bitfields - // is important as prevents them from occupying the same byte. If you remove - // this variable, make sure to maintain this property. - absl::once_flag init_control_; + 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_`). - // If def_kind_ == kDynamicValue, default_value_ holds a dynamically allocated - // value. - uint8_t def_kind_ : 1 ABSL_GUARDED_BY(*DataGuard()); + // 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. @@ -530,9 +595,7 @@ class FlagImpl { // 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_ ABSL_GUARDED_BY(*DataGuard()); - // Current Flag Value - FlagValue value_; + 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. @@ -549,11 +612,29 @@ class FlagImpl { // flag reflection handle interface. template <typename T> -class Flag final : public flags_internal::CommandLineFlag { +class Flag { public: - constexpr Flag(const char* name, const char* filename, const FlagHelpArg help, - const FlagDfltGenFunc default_value_gen) - : impl_(name, filename, &FlagOps<T>, help, default_value_gen) {} + 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(). @@ -564,106 +645,129 @@ class Flag final : public flags_internal::CommandLineFlag { }; U u; - impl_.Get(&u.value); +#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_.Set(v); } - void SetCallback(const FlagCallbackFunc mutation_callback) { - impl_.SetCallback(mutation_callback); + void Set(const T& v) { + impl_.AssertValidType(base_internal::FastTypeId<T>(), &GenRuntimeTypeId<T>); + impl_.Write(&v); } - // CommandLineFlag interface - absl::string_view Name() const override { return impl_.Name(); } - std::string Filename() const override { return impl_.Filename(); } - absl::string_view Typename() const override { return ""; } - std::string Help() const override { return impl_.Help(); } - bool IsModified() const override { return impl_.IsModified(); } - bool IsSpecifiedOnCommandLine() const override { - return impl_.IsSpecifiedOnCommandLine(); - } - std::string DefaultValue() const override { return impl_.DefaultValue(); } - std::string CurrentValue() const override { return impl_.CurrentValue(); } - bool ValidateInputValue(absl::string_view value) const override { - return impl_.ValidateInputValue(value); - } + // Access to the reflection. + const CommandLineFlag& Reflect() const { return impl_; } - // 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 { - return impl_.SaveState(this); - } + // 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_; +}; - // Restores the flag state to the supplied state object. If there is - // nothing to restore returns false. Otherwise returns true. - bool RestoreState(const FlagState<T>& flag_state) { - return impl_.RestoreState(&flag_state.cur_value_, flag_state.modified_, - flag_state.on_command_line_, flag_state.counter_); +/////////////////////////////////////////////////////////////////////////////// +// Trampoline for friend access + +class FlagImplPeer { + public: + template <typename T, typename FlagType> + static T InvokeGet(const FlagType& flag) { + return flag.Get(); } - bool SetFromString(absl::string_view value, FlagSettingMode set_mode, - ValueSource source, std::string* error) override { - return impl_.SetFromString(value, set_mode, source, error); + template <typename FlagType, typename T> + static void InvokeSet(FlagType& flag, const T& v) { + flag.Set(v); } - void CheckDefaultValueParsingRoundtrip() const override { - impl_.CheckDefaultValueParsingRoundtrip(); + template <typename FlagType> + static const CommandLineFlag& InvokeReflect(const FlagType& f) { + return f.Reflect(); } - - private: - friend class FlagState<T>; - - void Read(void* dst) const override { impl_.Read(dst); } - FlagStaticTypeId TypeId() const override { return &FlagStaticTypeIdGen<T>; } - - // Flag's data - FlagImpl impl_; }; +/////////////////////////////////////////////////////////////////////////////// +// Implementation of Flag value specific operations routine. template <typename T> -inline void FlagState<T>::Restore() const { - if (flag_->RestoreState(*this)) { - ABSL_INTERNAL_LOG(INFO, - absl::StrCat("Restore saved value of ", flag_->Name(), - " to: ", flag_->CurrentValue())); +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_); + explicit FlagRegistrar(Flag<T>& flag) : flag_(flag) { + if (do_register) flags_internal::RegisterCommandLineFlag(flag_.impl_); } - FlagRegistrar& OnUpdate(FlagCallbackFunc cb) && { - flag_->SetCallback(cb); + FlagRegistrar OnUpdate(FlagCallbackFunc cb) && { + flag_.impl_.SetCallback(cb); return *this; } - // Make the registrar "die" gracefully as a bool on a line where registration - // happens. Registrar objects are intended to live only as temporary. - operator bool() const { return true; } // NOLINT + // 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). + Flag<T>& flag_; // Flag being registered (not owned). }; -// This struct and corresponding overload to MakeDefaultValue are used to -// facilitate usage of {} as default value in ABSL_FLAG macro. -struct EmptyBraces {}; - -template <typename T> -T* MakeFromDefaultValue(T t) { - return new T(std::move(t)); -} - -template <typename T> -T* MakeFromDefaultValue(EmptyBraces) { - return new T; -} - } // namespace flags_internal ABSL_NAMESPACE_END } // namespace absl |