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Export of internal Abseil changes

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--
990253454819ce26ff1dda9ab4bbc145b61d01e4 by Xiaoyi Zhang <zhangxy@google.com>:

Import github PR https://github.com/abseil/abseil-cpp/pull/645

PiperOrigin-RevId: 303119797

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5ac845cb7929b7d1eaf59a309afd811db5001175 by Abseil Team <absl-team@google.com>:

Fix internal exception spec compatibility error

PiperOrigin-RevId: 303104081

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3290595dd866eecab3c7044e2e3ca0adb74f1bf5 by Gennadiy Rozental <rogeeff@google.com>:

Use FlagValue<T> to represent the value of a flag. Place it directly after
FlagImpl and use a computed offset refer to it.

The offset is computed based on the assumption that the `value_` data member
is placed directly after the impl_ data member in Flag<T>.

This change will allow us to migrate to `T`-specific storage in the generic case.

This change decreases the overhead for int flags by 32 bytes.

PiperOrigin-RevId: 303038099

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f2b37722cd7a6d3a60ef9713f0d2bbff56f3ddbf by Derek Mauro <dmauro@google.com>:

Minor correctness fix for an ABSL_HAVE_BUILTIN conditional

PiperOrigin-RevId: 302980666

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39c079a6141ae1c5728af8bf33a39c8aff9deb9f by Abseil Team <absl-team@google.com>:

Use ABSL_HARDENING_ASSERT in b-tree and SwissTable iterators.

PiperOrigin-RevId: 302970075

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9668a044e080c789df32bcaa1ffb5100831cd9fa by Benjamin Barenblat <bbaren@google.com>:

Correct `add_subdirectory` line in CMake googletest support

Commit bcefbdcdf6 added support for building with CMake against a local googletest checkout, but I missed a line when constructing the diff. Change the `add_subdirectory` line to reference the correct directories.

PiperOrigin-RevId: 302947488

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0a3c10fabf80a43ca69ab8b1570030e55f2be741 by Andy Soffer <asoffer@google.com>:

Remove unused distribution format traits.

PiperOrigin-RevId: 302896176

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0478f2f6270e5ed64c0e28ec09556ca90b2d46a9 by Samuel Benzaquen <sbenza@google.com>:

Fix for CWG:2310.

PiperOrigin-RevId: 302734089

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3cb978dda5cae5905affdc0914dcc2d27671ed11 by Samuel Benzaquen <sbenza@google.com>:

Fix the Allocate/Deallocate functions to use the same underlying allocator type.

PiperOrigin-RevId: 302721804

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ae38d3984fb68b4e3ddc165fa8d5c24d5936be52 by Matthew Brown <matthewbr@google.com>:

Internal Change

PiperOrigin-RevId: 302717314

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7357cf7abd03cc60b6e82b5f28a8e34935c3b4dc by Andy Getzendanner <durandal@google.com>:

Fix typo: s/ABSL_HARDENED_ASSERT/ABSL_HARDENING_ASSERT/

PiperOrigin-RevId: 302532164
GitOrigin-RevId: 990253454819ce26ff1dda9ab4bbc145b61d01e4
Change-Id: Ie595a221c16e1e7e1255ad42e029b646c5f3e11d
This commit is contained in:
Abseil Team 2020-03-26 08:48:01 -07:00 • committed by Xiaoyi Zhang
parent 132d791b40
commit 79e0dc1151
29 changed files with 387 additions and 607 deletions
Download patch file Download diff file Expand all files Collapse all files

259
absl/flags/internal/flag.h
View file

@ -53,56 +53,13 @@ enum class FlagOp {
kStaticTypeId,
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: {
auto* static_id = &FlagStaticTypeIdGen<T>;
// Cast from function pointer to void* is not portable.
// We don't have an easy way to work around this, but it works fine
// on all the platforms we test and as long as size of pointers match
// we should be fine to do reinterpret cast.
static_assert(sizeof(void*) == sizeof(static_id),
"Flag's static type id does not work on this platform");
return reinterpret_cast<void*>(static_id);
}
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) {
@ -144,6 +101,16 @@ inline FlagStaticTypeId StaticTypeId(FlagOpFn op) {
return reinterpret_cast<FlagStaticTypeId>(
op(FlagOp::kStaticTypeId, 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)));
}
///////////////////////////////////////////////////////////////////////////////
// Flag help auxiliary structs.
@ -239,6 +206,10 @@ using FlagUseOneWordStorage = std::integral_constant<
struct alignas(16) AlignedTwoWords {
int64_t first;
int64_t second;
bool IsInitialized() const {
return first != flags_internal::UninitializedFlagValue();
}
};
template <typename T>
@ -248,8 +219,14 @@ using FlagUseTwoWordsStorage = std::integral_constant<
#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) {}
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
@ -269,23 +246,70 @@ enum class FlagValueStorageKind : uint8_t {
kTwoWordsAtomic = 2
};
union FlagValue {
constexpr explicit FlagValue(int64_t v) : one_word_atomic(v) {}
template <typename T>
static constexpr FlagValueStorageKind StorageKind() {
return FlagUseHeapStorage<T>::value
? FlagValueStorageKind::kHeapAllocated
: FlagUseOneWordStorage<T>::value
? FlagValueStorageKind::kOneWordAtomic
: FlagUseTwoWordsStorage<T>::value
? FlagValueStorageKind::kTwoWordsAtomic
: FlagValueStorageKind::kHeapAllocated;
}
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;
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;
};
struct FlagTwoWordsValue {
using value_type = std::atomic<AlignedTwoWords>;
constexpr FlagTwoWordsValue()
: value(AlignedTwoWords{UninitializedFlagValue(), 0}) {}
value_type value;
};
template <typename T,
FlagValueStorageKind Kind = flags_internal::StorageKind<T>()>
struct FlagValue;
template <typename T>
struct FlagValue<T, FlagValueStorageKind::kHeapAllocated>
: FlagHeapAllocatedValue {
bool Get(T*) const { return false; }
};
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;
}
};
void* dynamic;
std::atomic<int64_t> one_word_atomic;
std::atomic<flags_internal::AlignedTwoWords> two_words_atomic;
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;
}
};
///////////////////////////////////////////////////////////////////////////////
@ -333,35 +357,10 @@ class FlagImpl final : public flags_internal::CommandLineFlag {
counter_(0),
callback_(nullptr),
default_value_(default_value_gen),
value_(flags_internal::UninitializedFlagValue()),
data_guard_{} {}
// Constant access methods
void Read(void* dst) const override ABSL_LOCKS_EXCLUDED(*DataGuard());
template <typename T, typename std::enable_if<FlagUseHeapStorage<T>::value,
int>::type = 0>
void Get(T* dst) const {
Read(dst);
}
template <typename T, typename std::enable_if<FlagUseOneWordStorage<T>::value,
int>::type = 0>
void Get(T* dst) const {
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, 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
void Write(const void* src) ABSL_LOCKS_EXCLUDED(*DataGuard());
@ -391,6 +390,25 @@ class FlagImpl final : public flags_internal::CommandLineFlag {
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>
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;
// 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,
@ -488,13 +506,6 @@ class FlagImpl final : public flags_internal::CommandLineFlag {
// these two cases.
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
// initialized in FlagImpl::Init via placement new.
// We can't use "absl::Mutex data_guard_", since this class is not literal.
@ -514,8 +525,9 @@ 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, FlagValue::Kind<T>(),
default_value_gen) {}
: impl_(name, filename, &FlagOps<T>, help,
flags_internal::StorageKind<T>(), default_value_gen),
value_() {}
T Get() const {
// See implementation notes in CommandLineFlag::Get().
@ -530,7 +542,7 @@ class Flag {
impl_.AssertValidType(&flags_internal::FlagStaticTypeIdGen<T>);
#endif
impl_.Get(&u.value);
if (!value_.Get(&u.value)) impl_.Read(&u.value);
return std::move(u.value);
}
void Set(const T& v) {
@ -556,10 +568,63 @@ class Flag {
private:
template <typename U, bool do_register>
friend class FlagRegistrar;
// 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_;
};
///////////////////////////////////////////////////////////////////////////////
// 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::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*>(static_cast<uintptr_t>(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;
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);