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/* Copyright 2014 10gen Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects
* for all of the code used other than as permitted herein. If you modify
* file(s) with this exception, you may extend this exception to your
* version of the file(s), but you are not obligated to do so. If you do not
* wish to do so, delete this exception statement from your version. If you
* delete this exception statement from all source files in the program,
* then also delete it in the license file.
*/
#pragma once
#include <atomic>
#include <type_traits>
#include <boost/static_assert.hpp>
namespace mongo {
/**
* Implementation of the AtomicWord interface in terms of the C++11 Atomics.
*/
template <typename _WordType>
class AtomicWord {
public:
/**
* Underlying value type.
*/
typedef _WordType WordType;
/**
* Construct a new word with the given initial value.
*/
explicit AtomicWord(WordType value=WordType(0)) : _value(value) {}
/**
* Gets the current value of this AtomicWord.
*
* Has acquire and release semantics.
*/
WordType load() const {
return _value.load();
}
/**
* Gets the current value of this AtomicWord.
*
* Has relaxed semantics.
*/
WordType loadRelaxed() const {
return _value.load(std::memory_order_relaxed);
}
/**
* Sets the value of this AtomicWord to "newValue".
*
* Has acquire and release semantics.
*/
void store(WordType newValue) {
return _value.store(newValue);
}
/**
* Atomically swaps the current value of this with "newValue".
*
* Returns the old value.
*
* Has acquire and release semantics.
*/
WordType swap(WordType newValue) {
return _value.exchange(newValue);
}
/**
* Atomic compare and swap.
*
* If this value equals "expected", sets this to "newValue".
* Always returns the original of this.
*
* Has acquire and release semantics.
*/
WordType compareAndSwap(WordType expected, WordType newValue) {
// NOTE: Subtle: compare_exchange mutates its first argument.
_value.compare_exchange_strong(expected, newValue);
return expected;
}
/**
* Get the current value of this, add "increment" and store it, atomically.
*
* Returns the value of this before incrementing.
*
* Has acquire and release semantics.
*/
WordType fetchAndAdd(WordType increment) {
return _value.fetch_add(increment);
}
/**
* Get the current value of this, subtract "decrement" and store it, atomically.
*
* Returns the value of this before decrementing.
*
* Has acquire and release semantics.
*/
WordType fetchAndSubtract(WordType decrement) {
return _value.fetch_sub(decrement);
}
/**
* Get the current value of this, add "increment" and store it, atomically.
*
* Returns the value of this after incrementing.
*
* Has acquire and release semantics.
*/
WordType addAndFetch(WordType increment) {
return fetchAndAdd(increment) + increment;
}
/**
* Get the current value of this, subtract "decrement" and store it, atomically.
*
* Returns the value of this after decrementing.
*
* Has acquire and release semantics.
*/
WordType subtractAndFetch(WordType decrement) {
return fetchAndSubtract(decrement) - decrement;
}
private:
std::atomic<WordType> _value;
};
#define _ATOMIC_WORD_DECLARE(NAME, WTYPE) \
typedef class AtomicWord<WTYPE> NAME; \
namespace { \
BOOST_STATIC_ASSERT(sizeof(NAME) == sizeof(WTYPE)); \
BOOST_STATIC_ASSERT(std::is_standard_layout<WTYPE>::value); \
} // namespace
_ATOMIC_WORD_DECLARE(AtomicUInt32, unsigned);
_ATOMIC_WORD_DECLARE(AtomicUInt64, unsigned long long);
_ATOMIC_WORD_DECLARE(AtomicInt32, int);
_ATOMIC_WORD_DECLARE(AtomicInt64, long long);
#undef _ATOMIC_WORD_DECLARE
} // namespace mongo
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