// Copyright 2018 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.
#ifndef ABSL_CONTAINER_INTERNAL_CONTAINER_MEMORY_H_
#define ABSL_CONTAINER_INTERNAL_CONTAINER_MEMORY_H_
#include <cassert>
#include <cstddef>
#include <memory>
#include <new>
#include <tuple>
#include <type_traits>
#include <utility>
#include "absl/base/config.h"
#include "absl/memory/memory.h"
#include "absl/meta/type_traits.h"
#include "absl/utility/utility.h"
#ifdef ABSL_HAVE_ADDRESS_SANITIZER
#include <sanitizer/asan_interface.h>
#endif
#ifdef ABSL_HAVE_MEMORY_SANITIZER
#include <sanitizer/msan_interface.h>
#endif
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace container_internal {
template <size_t Alignment>
struct alignas(Alignment) AlignedType {};
// Allocates at least n bytes aligned to the specified alignment.
// Alignment must be a power of 2. It must be positive.
//
// Note that many allocators don't honor alignment requirements above certain
// threshold (usually either alignof(std::max_align_t) or alignof(void*)).
// Allocate() doesn't apply alignment corrections. If the underlying allocator
// returns insufficiently alignment pointer, that's what you are going to get.
template <size_t Alignment, class Alloc>
void* Allocate(Alloc* alloc, size_t n) {
static_assert(Alignment > 0, "");
assert(n && "n must be positive");
using M = AlignedType<Alignment>;
using A = typename absl::allocator_traits<Alloc>::template rebind_alloc<M>;
using AT = typename absl::allocator_traits<Alloc>::template rebind_traits<M>;
// On macOS, "mem_alloc" is a #define with one argument defined in
// rpc/types.h, so we can't name the variable "mem_alloc" and initialize it
// with the "foo(bar)" syntax.
A my_mem_alloc(*alloc);
void* p = AT::allocate(my_mem_alloc, (n + sizeof(M) - 1) / sizeof(M));
assert(reinterpret_cast<uintptr_t>(p) % Alignment == 0 &&
"allocator does not respect alignment");
return p;
}
// The pointer must have been previously obtained by calling
// Allocate<Alignment>(alloc, n).
template <size_t Alignment, class Alloc>
void Deallocate(Alloc* alloc, void* p, size_t n) {
static_assert(Alignment > 0, "");
assert(n && "n must be positive");
using M = AlignedType<Alignment>;
using A = typename absl::allocator_traits<Alloc>::template rebind_alloc<M>;
using AT = typename absl::allocator_traits<Alloc>::template rebind_traits<M>;
// On macOS, "mem_alloc" is a #define with one argument defined in
// rpc/types.h, so we can't name the variable "mem_alloc" and initialize it
// with the "foo(bar)" syntax.
A my_mem_alloc(*alloc);
AT::deallocate(my_mem_alloc, static_cast<M*>(p),
(n + sizeof(M) - 1) / sizeof(M));
}
namespace memory_internal {
// Constructs T into uninitialized storage pointed by `ptr` using the args
// specified in the tuple.
template <class Alloc, class T, class Tuple, size_t... I>
void ConstructFromTupleImpl(Alloc* alloc, T* ptr, Tuple&& t,
absl::index_sequence<I...>) {
absl::allocator_traits<Alloc>::construct(
*alloc, ptr, std::get<I>(std::forward<Tuple>(t))...);
}
template <class T, class F>
struct WithConstructedImplF {
template <class... Args>
decltype(std::declval<F>()(std::declval<T>())) operator()(
Args&&... args) const {
return std::forward<F>(f)(T(std::forward<Args>(args)...));
}
F&& f;
};
template <class T, class Tuple, size_t... Is, class F>
decltype(std::declval<F>()(std::declval<T>())) WithConstructedImpl(
Tuple&& t, absl::index_sequence<Is...>, F&& f) {
return WithConstructedImplF<T, F>{std::forward<F>(f)}(
std::get<Is>(std::forward<Tuple>(t))...);
}
template <class T, size_t... Is>
auto TupleRefImpl(T&& t, absl::index_sequence<Is...>)
-> decltype(std::forward_as_tuple(std::get<Is>(std::forward<T>(t))...)) {
return std::forward_as_tuple(std::get<Is>(std::forward<T>(t))...);
}
// Returns a tuple of references to the elements of the input tuple. T must be a
// tuple.
template <class T>
auto TupleRef(T&& t) -> decltype(
TupleRefImpl(std::forward<T>(t),
absl::make_index_sequence<
std::tuple_size<typename std::decay<T>::type>::value>())) {
return TupleRefImpl(
std::forward<T>(t),
absl::make_index_sequence<
std::tuple_size<typename std::decay<T>::type>::value>());
}
template <class F, class K, class V>
decltype(std::declval<F>()(std::declval<const K&>(), std::piecewise_construct,
std::declval<std::tuple<K>>(), std::declval<V>()))
DecomposePairImpl(F&& f, std::pair<std::tuple<K>, V> p) {
const auto& key = std::get<0>(p.first);
return std::forward<F>(f)(key, std::piecewise_construct, std::move(p.first),
std::move(p.second));
}
} // namespace memory_internal
// Constructs T into uninitialized storage pointed by `ptr` using the args
// specified in the tuple.
template <class Alloc, class T, class Tuple>
void ConstructFromTuple(Alloc* alloc, T* ptr, Tuple&& t) {
memory_internal::ConstructFromTupleImpl(
alloc, ptr, std::forward<Tuple>(t),
absl::make_index_sequence<
std::tuple_size<typename std::decay<Tuple>::type>::value>());
}
// Constructs T using the args specified in the tuple and calls F with the
// constructed value.
template <class T, class Tuple, class F>
decltype(std::declval<F>()(std::declval<T>())) WithConstructed(
Tuple&& t, F&& f) {
return memory_internal::WithConstructedImpl<T>(
std::forward<Tuple>(t),
absl::make_index_sequence<
std::tuple_size<typename std::decay<Tuple>::type>::value>(),
std::forward<F>(f));
}
// Given arguments of an std::pair's consructor, PairArgs() returns a pair of
// tuples with references to the passed arguments. The tuples contain
// constructor arguments for the first and the second elements of the pair.
//
// The following two snippets are equivalent.
//
// 1. std::pair<F, S> p(args...);
//
// 2. auto a = PairArgs(args...);
// std::pair<F, S> p(std::piecewise_construct,
// std::move(p.first), std::move(p.second));
inline std::pair<std::tuple<>, std::tuple<>> PairArgs() { return {}; }
template <class F, class S>
std::pair<std::tuple<F&&>, std::tuple<S&&>> PairArgs(F&& f, S&& s) {
return {std::piecewise_construct, std::forward_as_tuple(std::forward<F>(f)),
std::forward_as_tuple(std::forward<S>(s))};
}
template <class F, class S>
std::pair<std::tuple<const F&>, std::tuple<const S&>> PairArgs(
const std::pair<F, S>& p) {
return PairArgs(p.first, p.second);
}
template <class F, class S>
std::pair<std::tuple<F&&>, std::tuple<S&&>> PairArgs(std::pair<F, S>&& p) {
return PairArgs(std::forward<F>(p.first), std::forward<S>(p.second));
}
template <class F, class S>
auto PairArgs(std::piecewise_construct_t, F&& f, S&& s)
-> decltype(std::make_pair(memory_internal::TupleRef(std::forward<F>(f)),
memory_internal::TupleRef(std::forward<S>(s)))) {
return std::make_pair(memory_internal::TupleRef(std::forward<F>(f)),
memory_internal::TupleRef(std::forward<S>(s)));
}
// A helper function for implementing apply() in map policies.
template <class F, class... Args>
auto DecomposePair(F&& f, Args&&... args)
-> decltype(memory_internal::DecomposePairImpl(
std::forward<F>(f), PairArgs(std::forward<Args>(args)...))) {
return memory_internal::DecomposePairImpl(
std::forward<F>(f), PairArgs(std::forward<Args>(args)...));
}
// A helper function for implementing apply() in set policies.
template <class F, class Arg>
decltype(std::declval<F>()(std::declval<const Arg&>(), std::declval<Arg>()))
DecomposeValue(F&& f, Arg&& arg) {
const auto& key = arg;
return std::forward<F>(f)(key, std::forward<Arg>(arg));
}
// Helper functions for asan and msan.
inline void SanitizerPoisonMemoryRegion(const void* m, size_t s) {
#ifdef ABSL_HAVE_ADDRESS_SANITIZER
ASAN_POISON_MEMORY_REGION(m, s);
#endif
#ifdef ABSL_HAVE_MEMORY_SANITIZER
__msan_poison(m, s);
#endif
(void)m;
(void)s;
}
inline void SanitizerUnpoisonMemoryRegion(const void* m, size_t s) {
#ifdef ABSL_HAVE_ADDRESS_SANITIZER
ASAN_UNPOISON_MEMORY_REGION(m, s);
#endif
#ifdef ABSL_HAVE_MEMORY_SANITIZER
__msan_unpoison(m, s);
#endif
(void)m;
(void)s;
}
template <typename T>
inline void SanitizerPoisonObject(const T* object) {
SanitizerPoisonMemoryRegion(object, sizeof(T));
}
template <typename T>
inline void SanitizerUnpoisonObject(const T* object) {
SanitizerUnpoisonMemoryRegion(object, sizeof(T));
}
namespace memory_internal {
// If Pair is a standard-layout type, OffsetOf<Pair>::kFirst and
// OffsetOf<Pair>::kSecond are equivalent to offsetof(Pair, first) and
// offsetof(Pair, second) respectively. Otherwise they are -1.
//
// The purpose of OffsetOf is to avoid calling offsetof() on non-standard-layout
// type, which is non-portable.
template <class Pair, class = std::true_type>
struct OffsetOf {
static constexpr size_t kFirst = static_cast<size_t>(-1);
static constexpr size_t kSecond = static_cast<size_t>(-1);
};
template <class Pair>
struct OffsetOf<Pair, typename std::is_standard_layout<Pair>::type> {
static constexpr size_t kFirst = offsetof(Pair, first);
static constexpr size_t kSecond = offsetof(Pair, second);
};
template <class K, class V>
struct IsLayoutCompatible {
private:
struct Pair {
K first;
V second;
};
// Is P layout-compatible with Pair?
template <class P>
static constexpr bool LayoutCompatible() {
return std::is_standard_layout<P>() && sizeof(P) == sizeof(Pair) &&
alignof(P) == alignof(Pair) &&
memory_internal::OffsetOf<P>::kFirst ==
memory_internal::OffsetOf<Pair>::kFirst &&
memory_internal::OffsetOf<P>::kSecond ==
memory_internal::OffsetOf<Pair>::kSecond;
}
public:
// Whether pair<const K, V> and pair<K, V> are layout-compatible. If they are,
// then it is safe to store them in a union and read from either.
static constexpr bool value = std::is_standard_layout<K>() &&
std::is_standard_layout<Pair>() &&
memory_internal::OffsetOf<Pair>::kFirst == 0 &&
LayoutCompatible<std::pair<K, V>>() &&
LayoutCompatible<std::pair<const K, V>>();
};
} // namespace memory_internal
// The internal storage type for key-value containers like flat_hash_map.
//
// It is convenient for the value_type of a flat_hash_map<K, V> to be
// pair<const K, V>; the "const K" prevents accidental modification of the key
// when dealing with the reference returned from find() and similar methods.
// However, this creates other problems; we want to be able to emplace(K, V)
// efficiently with move operations, and similarly be able to move a
// pair<K, V> in insert().
//
// The solution is this union, which aliases the const and non-const versions
// of the pair. This also allows flat_hash_map<const K, V> to work, even though
// that has the same efficiency issues with move in emplace() and insert() -
// but people do it anyway.
//
// If kMutableKeys is false, only the value member can be accessed.
//
// If kMutableKeys is true, key can be accessed through all slots while value
// and mutable_value must be accessed only via INITIALIZED slots. Slots are
// created and destroyed via mutable_value so that the key can be moved later.
//
// Accessing one of the union fields while the other is active is safe as
// long as they are layout-compatible, which is guaranteed by the definition of
// kMutableKeys. For C++11, the relevant section of the standard is
// https://timsong-cpp.github.io/cppwp/n3337/class.mem#19 (9.2.19)
template <class K, class V>
union map_slot_type {
map_slot_type() {}
~map_slot_type() = delete;
using value_type = std::pair<const K, V>;
using mutable_value_type =
std::pair<absl::remove_const_t<K>, absl::remove_const_t<V>>;
value_type value;
mutable_value_type mutable_value;
absl::remove_const_t<K> key;
};
template <class K, class V>
struct map_slot_policy {
using slot_type = map_slot_type<K, V>;
using value_type = std::pair<const K, V>;
using mutable_value_type = std::pair<K, V>;
private:
static void emplace(slot_type* slot) {
// The construction of union doesn't do anything at runtime but it allows us
// to access its members without violating aliasing rules.
new (slot) slot_type;
}
// If pair<const K, V> and pair<K, V> are layout-compatible, we can accept one
// or the other via slot_type. We are also free to access the key via
// slot_type::key in this case.
using kMutableKeys = memory_internal::IsLayoutCompatible<K, V>;
public:
static value_type& element(slot_type* slot) { return slot->value; }
static const value_type& element(const slot_type* slot) {
return slot->value;
}
// When C++17 is available, we can use std::launder to provide mutable
// access to the key for use in node handle.
#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606
static K& mutable_key(slot_type* slot) {
// Still check for kMutableKeys so that we can avoid calling std::launder
// unless necessary because it can interfere with optimizations.
return kMutableKeys::value ? slot->key
: *std::launder(const_cast<K*>(
std::addressof(slot->value.first)));
}
#else // !(defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606)
static const K& mutable_key(slot_type* slot) { return key(slot); }
#endif
static const K& key(const slot_type* slot) {
return kMutableKeys::value ? slot->key : slot->value.first;
}
template <class Allocator, class... Args>
static void construct(Allocator* alloc, slot_type* slot, Args&&... args) {
emplace(slot);
if (kMutableKeys::value) {
absl::allocator_traits<Allocator>::construct(*alloc, &slot->mutable_value,
std::forward<Args>(args)...);
} else {
absl::allocator_traits<Allocator>::construct(*alloc, &slot->value,
std::forward<Args>(args)...);
}
}
// Construct this slot by moving from another slot.
template <class Allocator>
static void construct(Allocator* alloc, slot_type* slot, slot_type* other) {
emplace(slot);
if (kMutableKeys::value) {
absl::allocator_traits<Allocator>::construct(
*alloc, &slot->mutable_value, std::move(other->mutable_value));
} else {
absl::allocator_traits<Allocator>::construct(*alloc, &slot->value,
std::move(other->value));
}
}
template <class Allocator>
static void destroy(Allocator* alloc, slot_type* slot) {
if (kMutableKeys::value) {
absl::allocator_traits<Allocator>::destroy(*alloc, &slot->mutable_value);
} else {
absl::allocator_traits<Allocator>::destroy(*alloc, &slot->value);
}
}
template <class Allocator>
static void transfer(Allocator* alloc, slot_type* new_slot,
slot_type* old_slot) {
emplace(new_slot);
if (kMutableKeys::value) {
absl::allocator_traits<Allocator>::construct(
*alloc, &new_slot->mutable_value, std::move(old_slot->mutable_value));
} else {
absl::allocator_traits<Allocator>::construct(*alloc, &new_slot->value,
std::move(old_slot->value));
}
destroy(alloc, old_slot);
}
template <class Allocator>
static void swap(Allocator* alloc, slot_type* a, slot_type* b) {
if (kMutableKeys::value) {
using std::swap;
swap(a->mutable_value, b->mutable_value);
} else {
value_type tmp = std::move(a->value);
absl::allocator_traits<Allocator>::destroy(*alloc, &a->value);
absl::allocator_traits<Allocator>::construct(*alloc, &a->value,
std::move(b->value));
absl::allocator_traits<Allocator>::destroy(*alloc, &b->value);
absl::allocator_traits<Allocator>::construct(*alloc, &b->value,
std::move(tmp));
}
}
template <class Allocator>
static void move(Allocator* alloc, slot_type* src, slot_type* dest) {
if (kMutableKeys::value) {
dest->mutable_value = std::move(src->mutable_value);
} else {
absl::allocator_traits<Allocator>::destroy(*alloc, &dest->value);
absl::allocator_traits<Allocator>::construct(*alloc, &dest->value,
std::move(src->value));
}
}
};
} // namespace container_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_CONTAINER_INTERNAL_CONTAINER_MEMORY_H_
