diff options
Diffstat (limited to 'absl/flags')
| -rw-r--r-- | absl/flags/BUILD.bazel | 4 | ||||
| -rw-r--r-- | absl/flags/CMakeLists.txt | 3 | ||||
| -rw-r--r-- | absl/flags/flag.h | 1 | ||||
| -rw-r--r-- | absl/flags/flag_benchmark.cc | 8 | ||||
| -rw-r--r-- | absl/flags/flag_test.cc | 143 | ||||
| -rw-r--r-- | absl/flags/internal/commandlineflag.cc | 30 | ||||
| -rw-r--r-- | absl/flags/internal/commandlineflag.h | 6 | ||||
| -rw-r--r-- | absl/flags/internal/flag.cc | 107 | ||||
| -rw-r--r-- | absl/flags/internal/flag.h | 208 |
9 files changed, 325 insertions, 185 deletions
diff --git a/absl/flags/BUILD.bazel b/absl/flags/BUILD.bazel index cdb4e7e8fe78..9166f74c1b6e 100644 --- a/absl/flags/BUILD.bazel +++ b/absl/flags/BUILD.bazel @@ -45,6 +45,7 @@ cc_library( "//absl/base:config", "//absl/base:core_headers", "//absl/memory", + "//absl/meta:type_traits", "//absl/strings", "//absl/synchronization", ], @@ -130,6 +131,9 @@ cc_library( cc_library( name = "handle", + srcs = [ + "internal/commandlineflag.cc", + ], hdrs = [ "internal/commandlineflag.h", ], diff --git a/absl/flags/CMakeLists.txt b/absl/flags/CMakeLists.txt index 1d25f0ded8b1..01cf09b1b52a 100644 --- a/absl/flags/CMakeLists.txt +++ b/absl/flags/CMakeLists.txt @@ -33,6 +33,7 @@ absl_cc_library( absl::flags_handle absl::flags_registry absl::synchronization + absl::meta PUBLIC ) @@ -117,6 +118,8 @@ absl_cc_library( absl_cc_library( NAME flags_handle + SRCS + "internal/commandlineflag.cc" HDRS "internal/commandlineflag.h" COPTS diff --git a/absl/flags/flag.h b/absl/flags/flag.h index cff02c1fcb61..bb917654d597 100644 --- a/absl/flags/flag.h +++ b/absl/flags/flag.h @@ -148,7 +148,6 @@ class Flag { return GetImpl()->template IsOfType<U>(); } T Get() const { return GetImpl()->Get(); } - bool AtomicGet(T* v) const { return GetImpl()->AtomicGet(v); } void Set(const T& v) { GetImpl()->Set(v); } void SetCallback(const flags_internal::FlagCallbackFunc mutation_callback) { GetImpl()->SetCallback(mutation_callback); diff --git a/absl/flags/flag_benchmark.cc b/absl/flags/flag_benchmark.cc index 87f731704c87..ff95bb5d7bfc 100644 --- a/absl/flags/flag_benchmark.cc +++ b/absl/flags/flag_benchmark.cc @@ -109,3 +109,11 @@ namespace { BENCHMARKED_TYPES(BM_GetFlag) } // namespace + +#define InvokeGetFlag(T) \ + T AbslInvokeGetFlag##T() { return absl::GetFlag(FLAGS_##T##_flag); } \ + int odr##T = (benchmark::DoNotOptimize(AbslInvokeGetFlag##T), 1); + +BENCHMARKED_TYPES(InvokeGetFlag) + +// To veiw disassembly use: gdb ${BINARY} -batch -ex "disassemble /s $FUNC" diff --git a/absl/flags/flag_test.cc b/absl/flags/flag_test.cc index 4984d28403b2..1e01b49cc4f2 100644 --- a/absl/flags/flag_test.cc +++ b/absl/flags/flag_test.cc @@ -49,28 +49,6 @@ void* TestMakeDflt() { } void TestCallback() {} -template <typename T> -bool TestConstructionFor() { - constexpr flags::FlagHelpArg help_arg{flags::FlagHelpMsg("literal help"), - flags::FlagHelpKind::kLiteral}; - constexpr flags::Flag<T> f1("f1", "file", help_arg, &TestMakeDflt<T>); - EXPECT_EQ(f1.Name(), "f1"); - EXPECT_EQ(f1.Help(), "literal help"); - EXPECT_EQ(f1.Filename(), "file"); - - ABSL_CONST_INIT static flags::Flag<T> f2( - "f2", "file", - {flags::FlagHelpMsg(&TestHelpMsg), flags::FlagHelpKind::kGenFunc}, - &TestMakeDflt<T>); - flags::FlagRegistrar<T, false>(&f2).OnUpdate(TestCallback); - - EXPECT_EQ(f2.Name(), "f2"); - EXPECT_EQ(f2.Help(), "dynamic help"); - EXPECT_EQ(f2.Filename(), "file"); - - return true; -} - struct UDT { UDT() = default; UDT(const UDT&) = default; @@ -98,19 +76,103 @@ class FlagTest : public testing::Test { } }; +struct S1 { + S1() = default; + S1(const S1&) = default; + int32_t f1; + int64_t f2; +}; + +struct S2 { + S2() = default; + S2(const S2&) = default; + int64_t f1; + double f2; +}; + +TEST_F(FlagTest, Traits) { + EXPECT_EQ(flags::FlagValue::Kind<int>(), + flags::FlagValueStorageKind::kOneWordAtomic); + EXPECT_EQ(flags::FlagValue::Kind<bool>(), + flags::FlagValueStorageKind::kOneWordAtomic); + EXPECT_EQ(flags::FlagValue::Kind<double>(), + flags::FlagValueStorageKind::kOneWordAtomic); + EXPECT_EQ(flags::FlagValue::Kind<int64_t>(), + flags::FlagValueStorageKind::kOneWordAtomic); + +#if defined(ABSL_FLAGS_INTERNAL_ATOMIC_DOUBLE_WORD) + EXPECT_EQ(flags::FlagValue::Kind<S1>(), + flags::FlagValueStorageKind::kTwoWordsAtomic); + EXPECT_EQ(flags::FlagValue::Kind<S2>(), + flags::FlagValueStorageKind::kTwoWordsAtomic); +#else + EXPECT_EQ(flags::FlagValue::Kind<S1>(), + flags::FlagValueStorageKind::kHeapAllocated); + EXPECT_EQ(flags::FlagValue::Kind<S2>(), + flags::FlagValueStorageKind::kHeapAllocated); +#endif + + EXPECT_EQ(flags::FlagValue::Kind<std::string>(), + flags::FlagValueStorageKind::kHeapAllocated); + EXPECT_EQ(flags::FlagValue::Kind<std::vector<std::string>>(), + flags::FlagValueStorageKind::kHeapAllocated); +} + +// -------------------------------------------------------------------- + +constexpr flags::FlagHelpArg help_arg{flags::FlagHelpMsg("literal help"), + flags::FlagHelpKind::kLiteral}; + +using String = std::string; + +#define DEFINE_CONSTRUCTED_FLAG(T) \ + constexpr flags::Flag<T> f1##T("f1", "file", help_arg, &TestMakeDflt<T>); \ + ABSL_CONST_INIT flags::Flag<T> f2##T( \ + "f2", "file", \ + {flags::FlagHelpMsg(&TestHelpMsg), flags::FlagHelpKind::kGenFunc}, \ + &TestMakeDflt<T>) + +#define TEST_CONSTRUCTED_FLAG(T) TestConstructionFor(f1##T, &f2##T); + +DEFINE_CONSTRUCTED_FLAG(bool); +DEFINE_CONSTRUCTED_FLAG(int16_t); +DEFINE_CONSTRUCTED_FLAG(uint16_t); +DEFINE_CONSTRUCTED_FLAG(int32_t); +DEFINE_CONSTRUCTED_FLAG(uint32_t); +DEFINE_CONSTRUCTED_FLAG(int64_t); +DEFINE_CONSTRUCTED_FLAG(uint64_t); +DEFINE_CONSTRUCTED_FLAG(float); +DEFINE_CONSTRUCTED_FLAG(double); +DEFINE_CONSTRUCTED_FLAG(String); +DEFINE_CONSTRUCTED_FLAG(UDT); + +template <typename T> +bool TestConstructionFor(const flags::Flag<T>& f1, flags::Flag<T>* f2) { + EXPECT_EQ(f1.Name(), "f1"); + EXPECT_EQ(f1.Help(), "literal help"); + EXPECT_EQ(f1.Filename(), "file"); + + flags::FlagRegistrar<T, false>(f2).OnUpdate(TestCallback); + + EXPECT_EQ(f2->Name(), "f2"); + EXPECT_EQ(f2->Help(), "dynamic help"); + EXPECT_EQ(f2->Filename(), "file"); + + return true; +} + TEST_F(FlagTest, TestConstruction) { - TestConstructionFor<bool>(); - TestConstructionFor<int16_t>(); - TestConstructionFor<uint16_t>(); - TestConstructionFor<int32_t>(); - TestConstructionFor<uint32_t>(); - TestConstructionFor<int64_t>(); - TestConstructionFor<uint64_t>(); - TestConstructionFor<double>(); - TestConstructionFor<float>(); - TestConstructionFor<std::string>(); - - TestConstructionFor<UDT>(); + TEST_CONSTRUCTED_FLAG(bool); + TEST_CONSTRUCTED_FLAG(int16_t); + TEST_CONSTRUCTED_FLAG(uint16_t); + TEST_CONSTRUCTED_FLAG(int32_t); + TEST_CONSTRUCTED_FLAG(uint32_t); + TEST_CONSTRUCTED_FLAG(int64_t); + TEST_CONSTRUCTED_FLAG(uint64_t); + TEST_CONSTRUCTED_FLAG(float); + TEST_CONSTRUCTED_FLAG(double); + TEST_CONSTRUCTED_FLAG(String); + TEST_CONSTRUCTED_FLAG(UDT); } // -------------------------------------------------------------------- @@ -391,17 +453,18 @@ TEST_F(FlagTest, TestCustomUDT) { using FlagDeathTest = FlagTest; TEST_F(FlagDeathTest, TestTypeMismatchValidations) { - EXPECT_DEBUG_DEATH( - static_cast<void>(absl::GetFlag(FLAGS_mistyped_int_flag)), - "Flag 'mistyped_int_flag' is defined as one type and declared " - "as another"); - EXPECT_DEATH(absl::SetFlag(&FLAGS_mistyped_int_flag, 1), +#if !defined(NDEBUG) + EXPECT_DEATH(static_cast<void>(absl::GetFlag(FLAGS_mistyped_int_flag)), "Flag 'mistyped_int_flag' is defined as one type and declared " "as another"); - EXPECT_DEATH(static_cast<void>(absl::GetFlag(FLAGS_mistyped_string_flag)), "Flag 'mistyped_string_flag' is defined as one type and " "declared as another"); +#endif + + EXPECT_DEATH(absl::SetFlag(&FLAGS_mistyped_int_flag, 1), + "Flag 'mistyped_int_flag' is defined as one type and declared " + "as another"); EXPECT_DEATH( absl::SetFlag(&FLAGS_mistyped_string_flag, std::vector<std::string>{}), "Flag 'mistyped_string_flag' is defined as one type and declared as " diff --git a/absl/flags/internal/commandlineflag.cc b/absl/flags/internal/commandlineflag.cc new file mode 100644 index 000000000000..90765a3eb6f3 --- /dev/null +++ b/absl/flags/internal/commandlineflag.cc @@ -0,0 +1,30 @@ +// +// Copyright 2020 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. + +#include "absl/flags/internal/commandlineflag.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace flags_internal { + +FlagStateInterface::~FlagStateInterface() {} + +bool CommandLineFlag::IsRetired() const { return false; } +bool CommandLineFlag::IsAbseilFlag() const { return true; } + +} // namespace flags_internal +ABSL_NAMESPACE_END +} // namespace absl + diff --git a/absl/flags/internal/commandlineflag.h b/absl/flags/internal/commandlineflag.h index 6363c6615b12..e91ddde633df 100644 --- a/absl/flags/internal/commandlineflag.h +++ b/absl/flags/internal/commandlineflag.h @@ -77,7 +77,7 @@ enum ValueSource { // of a flag produced this flag state from method CommandLineFlag::SaveState(). class FlagStateInterface { public: - virtual ~FlagStateInterface() {} + virtual ~FlagStateInterface(); // Restores the flag originated this object to the saved state. virtual void Restore() const = 0; @@ -146,9 +146,9 @@ class CommandLineFlag { // Returns help message associated with this flag. virtual std::string Help() const = 0; // Returns true iff this object corresponds to retired flag. - virtual bool IsRetired() const { return false; } + virtual bool IsRetired() const; // Returns true iff this is a handle to an Abseil Flag. - virtual bool IsAbseilFlag() const { return true; } + virtual bool IsAbseilFlag() const; // Returns id of the flag's value type. virtual FlagStaticTypeId TypeId() const = 0; virtual bool IsModified() const = 0; diff --git a/absl/flags/internal/flag.cc b/absl/flags/internal/flag.cc index 5a921e28d74e..a944e16e5083 100644 --- a/absl/flags/internal/flag.cc +++ b/absl/flags/internal/flag.cc @@ -77,19 +77,33 @@ class MutexRelock { void FlagImpl::Init() { new (&data_guard_) absl::Mutex; - absl::MutexLock lock(reinterpret_cast<absl::Mutex*>(&data_guard_)); - - value_.dynamic = MakeInitValue().release(); - StoreAtomic(); + // At this point the default_value_ always points to gen_func. + std::unique_ptr<void, DynValueDeleter> init_value( + (*default_value_.gen_func)(), DynValueDeleter{op_}); + switch (ValueStorageKind()) { + case FlagValueStorageKind::kHeapAllocated: + value_.dynamic = init_value.release(); + break; + case FlagValueStorageKind::kOneWordAtomic: { + int64_t atomic_value; + std::memcpy(&atomic_value, init_value.get(), Sizeof(op_)); + value_.one_word_atomic.store(atomic_value, std::memory_order_release); + break; + } + case FlagValueStorageKind::kTwoWordsAtomic: { + AlignedTwoWords atomic_value{0, 0}; + std::memcpy(&atomic_value, init_value.get(), Sizeof(op_)); + value_.two_words_atomic.store(atomic_value, std::memory_order_release); + break; + } + } } -// Ensures that the lazily initialized data is initialized, -// and returns pointer to the mutex guarding flags data. absl::Mutex* FlagImpl::DataGuard() const { absl::call_once(const_cast<FlagImpl*>(this)->init_control_, &FlagImpl::Init, const_cast<FlagImpl*>(this)); - // data_guard_ is initialized. + // data_guard_ is initialized inside Init. return reinterpret_cast<absl::Mutex*>(&data_guard_); } @@ -129,8 +143,24 @@ std::unique_ptr<void, DynValueDeleter> FlagImpl::MakeInitValue() const { } void FlagImpl::StoreValue(const void* src) { - flags_internal::Copy(op_, src, value_.dynamic); - StoreAtomic(); + switch (ValueStorageKind()) { + case FlagValueStorageKind::kHeapAllocated: + Copy(op_, src, value_.dynamic); + break; + case FlagValueStorageKind::kOneWordAtomic: { + int64_t one_word_val; + std::memcpy(&one_word_val, src, Sizeof(op_)); + value_.one_word_atomic.store(one_word_val, std::memory_order_release); + break; + } + case FlagValueStorageKind::kTwoWordsAtomic: { + AlignedTwoWords two_words_val{0, 0}; + std::memcpy(&two_words_val, src, Sizeof(op_)); + value_.two_words_atomic.store(two_words_val, std::memory_order_release); + break; + } + } + modified_ = true; ++counter_; InvokeCallback(); @@ -165,9 +195,25 @@ std::string FlagImpl::DefaultValue() const { } std::string FlagImpl::CurrentValue() const { - absl::MutexLock l(DataGuard()); + DataGuard(); // Make sure flag initialized + switch (ValueStorageKind()) { + case FlagValueStorageKind::kHeapAllocated: { + absl::MutexLock l(DataGuard()); + return flags_internal::Unparse(op_, value_.dynamic); + } + case FlagValueStorageKind::kOneWordAtomic: { + const auto one_word_val = + value_.one_word_atomic.load(std::memory_order_acquire); + return flags_internal::Unparse(op_, &one_word_val); + } + case FlagValueStorageKind::kTwoWordsAtomic: { + const auto two_words_val = + value_.two_words_atomic.load(std::memory_order_acquire); + return flags_internal::Unparse(op_, &two_words_val); + } + } - return flags_internal::Unparse(op_, value_.dynamic); + return ""; } void FlagImpl::SetCallback(const FlagCallbackFunc mutation_callback) { @@ -244,26 +290,27 @@ std::unique_ptr<void, DynValueDeleter> FlagImpl::TryParse( } void FlagImpl::Read(void* dst) const { - absl::ReaderMutexLock l(DataGuard()); + DataGuard(); // Make sure flag initialized + switch (ValueStorageKind()) { + case FlagValueStorageKind::kHeapAllocated: { + absl::MutexLock l(DataGuard()); - flags_internal::CopyConstruct(op_, value_.dynamic, dst); -} - -void FlagImpl::StoreAtomic() { - size_t data_size = flags_internal::Sizeof(op_); - - if (data_size <= sizeof(int64_t)) { - int64_t t = 0; - std::memcpy(&t, value_.dynamic, data_size); - value_.atomics.small_atomic.store(t, std::memory_order_release); - } -#if defined(ABSL_FLAGS_INTERNAL_ATOMIC_DOUBLE_WORD) - else if (data_size <= sizeof(FlagsInternalTwoWordsType)) { - FlagsInternalTwoWordsType t{0, 0}; - std::memcpy(&t, value_.dynamic, data_size); - value_.atomics.big_atomic.store(t, std::memory_order_release); + flags_internal::CopyConstruct(op_, value_.dynamic, dst); + break; + } + case FlagValueStorageKind::kOneWordAtomic: { + const auto one_word_val = + value_.one_word_atomic.load(std::memory_order_acquire); + std::memcpy(dst, &one_word_val, Sizeof(op_)); + break; + } + case FlagValueStorageKind::kTwoWordsAtomic: { + const auto two_words_val = + value_.two_words_atomic.load(std::memory_order_acquire); + std::memcpy(dst, &two_words_val, Sizeof(op_)); + break; + } } -#endif } void FlagImpl::Write(const void* src) { @@ -339,7 +386,7 @@ bool FlagImpl::SetFromString(absl::string_view value, FlagSettingMode set_mode, } if (!modified_) { - // Need to set both default value *and* current, in this case + // Need to set both default value *and* current, in this case. StoreValue(default_value_.dynamic_value); modified_ = false; } diff --git a/absl/flags/internal/flag.h b/absl/flags/internal/flag.h index 35a148cf6602..307b737752c9 100644 --- a/absl/flags/internal/flag.h +++ b/absl/flags/internal/flag.h @@ -31,6 +31,7 @@ #include "absl/flags/internal/commandlineflag.h" #include "absl/flags/internal/registry.h" #include "absl/memory/memory.h" +#include "absl/meta/type_traits.h" #include "absl/strings/str_cat.h" #include "absl/strings/string_view.h" #include "absl/synchronization/mutex.h" @@ -249,95 +250,66 @@ enum class FlagDefaultKind : uint8_t { kDynamicValue = 0, kGenFunc = 1 }; /////////////////////////////////////////////////////////////////////////////// // 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; +constexpr int64_t UninitializedFlagValue() { return 0xababababababababll; } -// 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 - -// 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; }; -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); -} - -constexpr int64_t SmallAtomicInit() { return 0xababababababababll; } - -template <typename T, typename S = void> -struct BestAtomicType { - using type = int64_t; - static constexpr int64_t AtomicInit() { return SmallAtomicInit(); } +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() = default; + constexpr AlignedTwoWords(int64_t, int64_t) {} }; +// This trait should be type dependent, otherwise SFINAE below will fail 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()}; - } +using FlagUseTwoWordsStorage = + std::integral_constant<bool, sizeof(T) != sizeof(T)>; +#endif + +template <typename T> +using FlagUseHeapStorage = + std::integral_constant<bool, !FlagUseOneWordStorage<T>::value && + !FlagUseTwoWordsStorage<T>::value>; + +enum class FlagValueStorageKind : uint8_t { + kHeapAllocated = 0, + kOneWordAtomic = 1, + kTwoWordsAtomic = 2 }; -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); - } +union FlagValue { + constexpr explicit FlagValue(int64_t v) : one_word_atomic(v) {} -#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); - } - constexpr Atomics() - : big_atomic{FlagsInternalTwoWordsType{SmallAtomicInit(), - SmallAtomicInit()}} {} -#else - constexpr Atomics() : small_atomic{SmallAtomicInit()} {} -#endif - }; - Atomics atomics{}; + template <typename T> + static constexpr FlagValueStorageKind Kind() { + return FlagUseHeapStorage<T>::value + ? FlagValueStorageKind::kHeapAllocated + : FlagUseOneWordStorage<T>::value + ? FlagValueStorageKind::kOneWordAtomic + : FlagUseTwoWordsStorage<T>::value + ? FlagValueStorageKind::kTwoWordsAtomic + : FlagValueStorageKind::kHeapAllocated; + } + + void* dynamic; + std::atomic<int64_t> one_word_atomic; + std::atomic<flags_internal::AlignedTwoWords> two_words_atomic; }; /////////////////////////////////////////////////////////////////////////////// @@ -369,18 +341,21 @@ struct DynValueDeleter { class FlagImpl { public: constexpr FlagImpl(const char* name, const char* filename, FlagOpFn op, - FlagHelpArg help, FlagDfltGenFunc default_value_gen) + FlagHelpArg help, FlagValueStorageKind value_kind, + FlagDfltGenFunc default_value_gen) : 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>(FlagDefaultKind::kGenFunc)), modified_(false), on_command_line_(false), counter_(0), callback_(nullptr), default_value_(default_value_gen), + value_(flags_internal::UninitializedFlagValue()), data_guard_{} {} // Constant access methods @@ -393,34 +368,29 @@ class FlagImpl { 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> + template <typename T, typename std::enable_if<FlagUseHeapStorage<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, + template <typename T, typename std::enable_if<FlagUseOneWordStorage<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); + int64_t one_word_val = + value_.one_word_atomic.load(std::memory_order_acquire); + if (ABSL_PREDICT_FALSE(one_word_val == UninitializedFlagValue())) { + DataGuard(); // Make sure flag initialized + one_word_val = value_.one_word_atomic.load(std::memory_order_acquire); } + std::memcpy(dst, static_cast<const void*>(&one_word_val), sizeof(T)); } - template <typename T> - void Set(const T& src) { - AssertValidType(&flags_internal::FlagStaticTypeIdGen<T>); - Write(&src); + template <typename T, typename std::enable_if< + FlagUseTwoWordsStorage<T>::value, int>::type = 0> + void Get(T* dst) const { + DataGuard(); // Make sure flag initialized + const auto two_words_val = + value_.two_words_atomic.load(std::memory_order_acquire); + std::memcpy(dst, &two_words_val, sizeof(T)); } // Mutating access methods @@ -428,9 +398,6 @@ class FlagImpl { 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) @@ -456,6 +423,14 @@ class FlagImpl { 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 `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; + private: // Ensures that `data_guard_` is initialized and returns it. absl::Mutex* DataGuard() const ABSL_LOCK_RETURNED((absl::Mutex*)&data_guard_); @@ -475,17 +450,13 @@ 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; // Immutable flag's state. @@ -499,6 +470,8 @@ 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 @@ -530,8 +503,13 @@ 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 + FlagDefaultSrc default_value_; + + // Atomically mutable flag's state + + // Flag's value. This can be either the atomically stored small value or + // pointer to the heap allocated dynamic value. value_storage_kind_ is used + // to distinguish these cases. FlagValue value_; // This is reserved space for an absl::Mutex to guard flag data. It will be @@ -553,7 +531,8 @@ class Flag final : public flags_internal::CommandLineFlag { 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) {} + : impl_(name, filename, &FlagOps<T>, help, FlagValue::Kind<T>(), + default_value_gen) {} T Get() const { // See implementation notes in CommandLineFlag::Get(). @@ -564,10 +543,17 @@ class Flag final : public flags_internal::CommandLineFlag { }; U u; +#if !defined(NDEBUG) + impl_.AssertValidType(&flags_internal::FlagStaticTypeIdGen<T>); +#endif + impl_.Get(&u.value); return std::move(u.value); } - void Set(const T& v) { impl_.Set(v); } + void Set(const T& v) { + impl_.AssertValidType(&flags_internal::FlagStaticTypeIdGen<T>); + impl_.Write(&v); + } void SetCallback(const FlagCallbackFunc mutation_callback) { impl_.SetCallback(mutation_callback); } @@ -619,7 +605,7 @@ class Flag final : public flags_internal::CommandLineFlag { }; template <typename T> -inline void FlagState<T>::Restore() const { +void FlagState<T>::Restore() const { if (flag_->RestoreState(*this)) { ABSL_INTERNAL_LOG(INFO, absl::StrCat("Restore saved value of ", flag_->Name(), |