atomic_intrinsics_gcc_sync.h

/*    Copyright 2014 10gen Inc.
 *
 *    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.
 */

#pragma once

#include <boost/utility.hpp>

namespace mongo {

template <typename T, typename IsTLarge = void>
class AtomicIntrinsics {
public:
    static T compareAndSwap(volatile T* dest, T expected, T newValue) {
        return __sync_val_compare_and_swap(dest, expected, newValue);
    }

    static T swap(volatile T* dest, T newValue) {
        T currentValue = *dest;
        while (true) {
            const T result = compareAndSwap(dest, currentValue, newValue);
            if (result == currentValue)
                return result;
            currentValue = result;
        }
    }

    static T load(volatile const T* value) {
        __sync_synchronize();
        T result = *value;
        __sync_synchronize();
        return result;
    }

    static T loadRelaxed(volatile const T* value) {
        asm volatile("" ::: "memory");
        return *value;
    }

    static void store(volatile T* dest, T newValue) {
        __sync_synchronize();
        *dest = newValue;
        __sync_synchronize();
    }

    static T fetchAndAdd(volatile T* dest, T increment) {
        return __sync_fetch_and_add(dest, increment);
    }

private:
    AtomicIntrinsics();
    ~AtomicIntrinsics();
};

template <typename T>
class AtomicIntrinsics<T, typename boost::disable_if_c<sizeof(T) <= sizeof(void*)>::type> {
public:
    static T compareAndSwap(volatile T* dest, T expected, T newValue) {
        return __sync_val_compare_and_swap(dest, expected, newValue);
    }

    static T swap(volatile T* dest, T newValue) {
        T currentValue = *dest;
        while (true) {
            const T result = compareAndSwap(dest, currentValue, newValue);
            if (result == currentValue)
                return result;
            currentValue = result;
        }
    }

    static T load(volatile const T* value) {
        return compareAndSwap(const_cast<volatile T*>(value), T(0), T(0));
    }

    static void store(volatile T* dest, T newValue) {
        swap(dest, newValue);
    }

    static T fetchAndAdd(volatile T* dest, T increment) {
        return __sync_fetch_and_add(dest, increment);
    }

private:
    AtomicIntrinsics();
    ~AtomicIntrinsics();
};

}  // namespace mongo