/*
 * 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.
 *
 * Copyright 2018 Danny Robson <danny@nerdcruft.net>
 */

#ifndef CRUFT_UTIL_JOB_SPINLOCK_HPP
#define CRUFT_UTIL_JOB_SPINLOCK_HPP

#include <atomic>

namespace util::job {
    /// a CPU intensive, but lower latency, lock.
    ///
    /// std::atomic_flag seems like it might have been a good option on which
    /// to base our implementation, but it appears potentially expensive to
    /// spin over without a cheap read operation.
    ///
    /// satisfies BasicLockable.
    class spinlock {
    public:
        spinlock ();
        spinlock (spinlock &&);
        spinlock& operator= (spinlock &&);

        spinlock (const spinlock&) = delete;
        spinlock& operator= (const spinlock&) = delete;

        void lock ();
        void unlock ();

    private:
        static_assert (
            std::atomic<bool>::is_always_lock_free,
            "we require a lock free primitive or the entire point is moot"
        );

        std::atomic<bool> held;
    };
};

#endif