diff options
Diffstat (limited to 'absl/flags/internal/flag.h')
| -rw-r--r-- | absl/flags/internal/flag.h | 103 |
1 files changed, 49 insertions, 54 deletions
diff --git a/absl/flags/internal/flag.h b/absl/flags/internal/flag.h index ae42dedcd633..2ae3dce3d13d 100644 --- a/absl/flags/internal/flag.h +++ b/absl/flags/internal/flag.h @@ -46,8 +46,8 @@ namespace flags_internal { // by function specific to that type with a signature matching FlagOpFn. enum class FlagOp { + kAlloc, kDelete, - kClone, kCopy, kCopyConstruct, kSizeof, @@ -63,13 +63,13 @@ using FlagOpFn = void* (*)(FlagOp, const void*, void*, void*); template <typename T> 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) { @@ -80,6 +80,12 @@ 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) { @@ -195,7 +201,7 @@ 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) @@ -253,46 +259,36 @@ using FlagUseTwoWordsStorage = #endif template <typename T> -using FlagUseHeapStorage = +using FlagUseBufferStorage = std::integral_constant<bool, !FlagUseOneWordStorage<T>::value && !FlagUseTwoWordsStorage<T>::value>; enum class FlagValueStorageKind : uint8_t { - kHeapAllocated = 0, + kAlignedBuffer = 0, kOneWordAtomic = 1, kTwoWordsAtomic = 2 }; template <typename T> static constexpr FlagValueStorageKind StorageKind() { - return FlagUseHeapStorage<T>::value - ? FlagValueStorageKind::kHeapAllocated + return FlagUseBufferStorage<T>::value + ? FlagValueStorageKind::kAlignedBuffer : FlagUseOneWordStorage<T>::value ? FlagValueStorageKind::kOneWordAtomic - : FlagUseTwoWordsStorage<T>::value - ? FlagValueStorageKind::kTwoWordsAtomic - : FlagValueStorageKind::kHeapAllocated; + : FlagValueStorageKind::kTwoWordsAtomic; } -struct FlagHeapAllocatedValue { - using value_type = void*; - - value_type value; -}; - struct FlagOneWordValue { - using value_type = std::atomic<int64_t>; constexpr FlagOneWordValue() : value(UninitializedFlagValue()) {} - value_type value; + std::atomic<int64_t> value; }; struct FlagTwoWordsValue { - using value_type = std::atomic<AlignedTwoWords>; constexpr FlagTwoWordsValue() : value(AlignedTwoWords{UninitializedFlagValue(), 0}) {} - value_type value; + std::atomic<AlignedTwoWords> value; }; template <typename T, @@ -300,9 +296,10 @@ template <typename T, struct FlagValue; template <typename T> -struct FlagValue<T, FlagValueStorageKind::kHeapAllocated> - : FlagHeapAllocatedValue { +struct FlagValue<T, FlagValueStorageKind::kAlignedBuffer> { bool Get(T*) const { return false; } + + alignas(T) char value[sizeof(T)]; }; template <typename T> @@ -347,10 +344,8 @@ 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) flags_internal::Delete(op, ptr); - } + explicit DynValueDeleter(FlagOpFn op_arg = nullptr); + void operator()(void* ptr) const; FlagOpFn op; }; @@ -416,10 +411,10 @@ class FlagImpl final : public flags_internal::CommandLineFlag { // 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> - typename StorageT::value_type& OffsetValue() const; - // This is an accessor for a value stored in heap allocated storage. - // Returns a mutable reference to a pointer to allow vlaue mutation. - void*& HeapAllocatedValue() const; + 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; @@ -492,17 +487,8 @@ class FlagImpl final : public flags_internal::CommandLineFlag { // 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_`). @@ -514,6 +500,9 @@ class FlagImpl final : public flags_internal::CommandLineFlag { // 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. @@ -600,11 +589,17 @@ class Flag { 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); + 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::kClone: - return new T(*static_cast<const T*>(v1)); + } case FlagOp::kCopy: *static_cast<T*>(v2) = *static_cast<const T*>(v1); return nullptr; @@ -675,13 +670,13 @@ class FlagRegistrar { struct EmptyBraces {}; template <typename T> -T* MakeFromDefaultValue(T t) { - return new T(std::move(t)); +void MakeFromDefaultValue(void* dst, T t) { + new (dst) T(std::move(t)); } template <typename T> -T* MakeFromDefaultValue(EmptyBraces) { - return new T{}; +void MakeFromDefaultValue(void* dst, EmptyBraces) { + new (dst) T{}; } } // namespace flags_internal |