diff options
Diffstat (limited to 'absl/flags/internal/flag.h')
| -rw-r--r-- | absl/flags/internal/flag.h | 83 |
1 files changed, 68 insertions, 15 deletions
diff --git a/absl/flags/internal/flag.h b/absl/flags/internal/flag.h index e6bade0a..6154638c 100644 --- a/absl/flags/internal/flag.h +++ b/absl/flags/internal/flag.h @@ -29,6 +29,7 @@ #include "absl/base/attributes.h" #include "absl/base/call_once.h" +#include "absl/base/casts.h" #include "absl/base/config.h" #include "absl/base/optimization.h" #include "absl/base/thread_annotations.h" @@ -162,7 +163,7 @@ inline ptrdiff_t ValueOffset(FlagOpFn op) { // Returns an address of RTTI's typeid(T). template <typename T> inline const std::type_info* GenRuntimeTypeId() { -#if defined(ABSL_FLAGS_INTERNAL_HAS_RTTI) +#ifdef ABSL_INTERNAL_HAS_RTTI return &typeid(T); #else return nullptr; @@ -289,7 +290,7 @@ constexpr T InitDefaultValue(EmptyBraces) { template <typename ValueT, typename GenT, typename std::enable_if<std::is_integral<ValueT>::value, int>::type = - (GenT{}, 0)> + ((void)GenT{}, 0)> constexpr FlagDefaultArg DefaultArg(int) { return {FlagDefaultSrc(GenT{}.value), FlagDefaultKind::kOneWord}; } @@ -302,7 +303,14 @@ constexpr FlagDefaultArg DefaultArg(char) { /////////////////////////////////////////////////////////////////////////////// // Flag current value auxiliary structs. -constexpr int64_t UninitializedFlagValue() { return 0xababababababababll; } +constexpr int64_t UninitializedFlagValue() { + return static_cast<int64_t>(0xababababababababll); +} + +template <typename T> +using FlagUseValueAndInitBitStorage = std::integral_constant< + bool, absl::type_traits_internal::is_trivially_copyable<T>::value && + std::is_default_constructible<T>::value && (sizeof(T) < 8)>; template <typename T> using FlagUseOneWordStorage = std::integral_constant< @@ -310,43 +318,61 @@ using FlagUseOneWordStorage = std::integral_constant< (sizeof(T) <= 8)>; template <class T> -using FlagShouldUseSequenceLock = std::integral_constant< +using FlagUseSequenceLockStorage = std::integral_constant< bool, absl::type_traits_internal::is_trivially_copyable<T>::value && (sizeof(T) > 8)>; enum class FlagValueStorageKind : uint8_t { - kAlignedBuffer = 0, + kValueAndInitBit = 0, kOneWordAtomic = 1, kSequenceLocked = 2, + kAlignedBuffer = 3, }; template <typename T> static constexpr FlagValueStorageKind StorageKind() { - return FlagUseOneWordStorage<T>::value ? FlagValueStorageKind::kOneWordAtomic - : FlagShouldUseSequenceLock<T>::value + return FlagUseValueAndInitBitStorage<T>::value + ? FlagValueStorageKind::kValueAndInitBit + : FlagUseOneWordStorage<T>::value + ? FlagValueStorageKind::kOneWordAtomic + : FlagUseSequenceLockStorage<T>::value ? FlagValueStorageKind::kSequenceLocked : FlagValueStorageKind::kAlignedBuffer; } struct FlagOneWordValue { - constexpr FlagOneWordValue() : value(UninitializedFlagValue()) {} - + constexpr explicit FlagOneWordValue(int64_t v) : value(v) {} std::atomic<int64_t> value; }; +template <typename T> +struct alignas(8) FlagValueAndInitBit { + T value; + // Use an int instead of a bool to guarantee that a non-zero value has + // a bit set. + uint8_t init; +}; + template <typename T, FlagValueStorageKind Kind = flags_internal::StorageKind<T>()> struct FlagValue; template <typename T> -struct FlagValue<T, FlagValueStorageKind::kAlignedBuffer> { - bool Get(const SequenceLock&, T&) const { return false; } - - alignas(T) char value[sizeof(T)]; +struct FlagValue<T, FlagValueStorageKind::kValueAndInitBit> : FlagOneWordValue { + constexpr FlagValue() : FlagOneWordValue(0) {} + bool Get(const SequenceLock&, T& dst) const { + int64_t storage = value.load(std::memory_order_acquire); + if (ABSL_PREDICT_FALSE(storage == 0)) { + return false; + } + dst = absl::bit_cast<FlagValueAndInitBit<T>>(storage).value; + return true; + } }; template <typename T> struct FlagValue<T, FlagValueStorageKind::kOneWordAtomic> : FlagOneWordValue { + constexpr FlagValue() : FlagOneWordValue(UninitializedFlagValue()) {} bool Get(const SequenceLock&, T& dst) const { int64_t one_word_val = value.load(std::memory_order_acquire); if (ABSL_PREDICT_FALSE(one_word_val == UninitializedFlagValue())) { @@ -370,6 +396,13 @@ struct FlagValue<T, FlagValueStorageKind::kSequenceLocked> { std::atomic<uint64_t>) std::atomic<uint64_t> value_words[kNumWords]; }; +template <typename T> +struct FlagValue<T, FlagValueStorageKind::kAlignedBuffer> { + bool Get(const SequenceLock&, T&) const { return false; } + + alignas(T) char value[sizeof(T)]; +}; + /////////////////////////////////////////////////////////////////////////////// // Flag callback auxiliary structs. @@ -415,7 +448,27 @@ class FlagImpl final : public CommandLineFlag { data_guard_{} {} // Constant access methods + int64_t ReadOneWord() const ABSL_LOCKS_EXCLUDED(*DataGuard()); + bool ReadOneBool() const ABSL_LOCKS_EXCLUDED(*DataGuard()); void Read(void* dst) const override ABSL_LOCKS_EXCLUDED(*DataGuard()); + void Read(bool* value) const ABSL_LOCKS_EXCLUDED(*DataGuard()) { + *value = ReadOneBool(); + } + template <typename T, + absl::enable_if_t<flags_internal::StorageKind<T>() == + FlagValueStorageKind::kOneWordAtomic, + int> = 0> + void Read(T* value) const ABSL_LOCKS_EXCLUDED(*DataGuard()) { + int64_t v = ReadOneWord(); + std::memcpy(value, static_cast<const void*>(&v), sizeof(T)); + } + template <typename T, + typename std::enable_if<flags_internal::StorageKind<T>() == + FlagValueStorageKind::kValueAndInitBit, + int>::type = 0> + void Read(T* value) const ABSL_LOCKS_EXCLUDED(*DataGuard()) { + *value = absl::bit_cast<FlagValueAndInitBit<T>>(ReadOneWord()).value; + } // Mutating access methods void Write(const void* src) ABSL_LOCKS_EXCLUDED(*DataGuard()); @@ -704,8 +757,8 @@ void* FlagOps(FlagOp op, const void* v1, void* v2, void* v3) { 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 = + size_t round_to = alignof(FlagValue<T>); + size_t offset = (sizeof(FlagImpl) + round_to - 1) / round_to * round_to; return reinterpret_cast<void*>(offset); } |