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+/* Copyright (c) 2020, 2021, 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 */
+
+#pragma once
+#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() {}
+
+ Type load(std::memory_order o= std::memory_order_relaxed) const
+ { return m.load(o); }
+ void store(Type i, std::memory_order o= std::memory_order_relaxed)
+ { m.store(i, o); }
+ operator Type() const { return m.load(); }
+ Type operator=(const Type i) { store(i); return i; }
+ 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); }
+ Type fetch_xor(const Type i, std::memory_order o= std::memory_order_relaxed)
+ { return m.fetch_xor(i, o); }
+ Type fetch_and(const Type i, std::memory_order o= std::memory_order_relaxed)
+ { return m.fetch_and(i, o); }
+ Type fetch_or(const Type i, std::memory_order o= std::memory_order_relaxed)
+ { return m.fetch_or(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 */