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/* Copyright (c) 2020, MariaDB | ||
This program is free software; you can redistribute it and/or modify | ||
it under the terms of the GNU General Public License as published by | ||
the Free Software Foundation; version 2 of the License. | ||
This program is distributed in the hope that it will be useful, | ||
but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
GNU General Public License for more details. | ||
You should have received a copy of the GNU General Public License | ||
along with this program; if not, write to the Free Software | ||
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335 USA */ | ||
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||
#ifdef __cplusplus | ||
#include <atomic> | ||
/** | ||
A wrapper for std::atomic, defaulting to std::memory_order_relaxed. | ||
When it comes to atomic loads or stores at std::memory_order_relaxed | ||
on IA-32 or AMD64, this wrapper is only introducing some constraints | ||
to the C++ compiler, to prevent some optimizations of loads or | ||
stores. | ||
On POWER and ARM, atomic loads and stores involve different instructions | ||
from normal loads and stores and will thus incur some overhead. | ||
Because atomic read-modify-write operations will always incur | ||
overhead, we intentionally do not define | ||
operator++(), operator--(), operator+=(), operator-=(), or similar, | ||
to make the overhead stand out in the users of this code. | ||
*/ | ||
template <typename Type> class Atomic_relaxed | ||
{ | ||
std::atomic<Type> m; | ||
public: | ||
Atomic_relaxed(const Atomic_relaxed<Type> &rhs) | ||
{ m.store(rhs, std::memory_order_relaxed); } | ||
Atomic_relaxed(Type val) : m(val) {} | ||
Atomic_relaxed() {} | ||
|
||
operator Type() const { return m.load(std::memory_order_relaxed); } | ||
Type operator=(const Type val) | ||
{ m.store(val, std::memory_order_relaxed); return val; } | ||
Type operator=(const Atomic_relaxed<Type> &rhs) { return *this= Type{rhs}; } | ||
Type fetch_add(const Type i, std::memory_order o= std::memory_order_relaxed) | ||
{ return m.fetch_add(i, o); } | ||
Type fetch_sub(const Type i, std::memory_order o= std::memory_order_relaxed) | ||
{ return m.fetch_sub(i, o); } | ||
bool compare_exchange_strong(Type& i1, const Type i2, | ||
std::memory_order o1= std::memory_order_relaxed, | ||
std::memory_order o2= std::memory_order_relaxed) | ||
{ return m.compare_exchange_strong(i1, i2, o1, o2); } | ||
Type exchange(const Type i, std::memory_order o= std::memory_order_relaxed) | ||
{ return m.exchange(i, o); } | ||
}; | ||
#endif /* __cplusplus */ |
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