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/*
* Copyright (C) 2022 The Android Open Source Project
*
* 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
*
* http://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 ART_RUNTIME_BASE_ATOMIC_PAIR_H_
#define ART_RUNTIME_BASE_ATOMIC_PAIR_H_
#include "base/macros.h"
#include <type_traits>
namespace art {
// std::pair<> is not trivially copyable and as such it is unsuitable for atomic operations.
template <typename IntType>
struct PACKED(2 * sizeof(IntType)) AtomicPair {
static_assert(std::is_integral_v<IntType>);
constexpr AtomicPair() : first(0), second(0) { }
AtomicPair(IntType f, IntType s) : first(f), second(s) { }
AtomicPair(const AtomicPair&) = default;
AtomicPair& operator=(const AtomicPair&) = default;
IntType first;
IntType second;
};
template <typename IntType>
ALWAYS_INLINE static inline AtomicPair<IntType> AtomicPairLoadAcquire(
std::atomic<AtomicPair<IntType>>* target) {
static_assert(std::atomic<AtomicPair<IntType>>::is_always_lock_free);
return target->load(std::memory_order_acquire);
}
template <typename IntType>
ALWAYS_INLINE static inline void AtomicPairStoreRelease(
std::atomic<AtomicPair<IntType>>* target, AtomicPair<IntType> value) {
static_assert(std::atomic<AtomicPair<IntType>>::is_always_lock_free);
target->store(value, std::memory_order_release);
}
// llvm does not implement 16-byte atomic operations on x86-64.
#if defined(__x86_64__)
ALWAYS_INLINE static inline AtomicPair<uint64_t> AtomicPairLoadAcquire(
std::atomic<AtomicPair<uint64_t>>* target) {
uint64_t first, second;
__asm__ __volatile__(
"lock cmpxchg16b (%2)"
: "=&a"(first), "=&d"(second)
: "r"(target), "a"(0), "d"(0), "b"(0), "c"(0)
: "cc");
return {first, second};
}
ALWAYS_INLINE static inline void AtomicPairStoreRelease(
std::atomic<AtomicPair<uint64_t>>* target, AtomicPair<uint64_t> value) {
uint64_t first, second;
__asm__ __volatile__ (
"movq (%2), %%rax\n\t"
"movq 8(%2), %%rdx\n\t"
"1:\n\t"
"lock cmpxchg16b (%2)\n\t"
"jnz 1b"
: "=&a"(first), "=&d"(second)
: "r"(target), "b"(value.first), "c"(value.second)
: "cc");
}
#endif // defined(__x86_64__)
} // namespace art
#endif // ART_RUNTIME_BASE_ATOMIC_PAIR_H_
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