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root/uspace/lib/cpp/include/__bits/refcount_obj.hpp

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/*
 * Copyright (c) 2019 Jaroslav Jindrak
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef LIBCPP_BITS_REFCOUNT_OBJ
#define LIBCPP_BITS_REFCOUNT_OBJ

namespace std::aux
{
    /**
     * At the moment we do not have atomics, change this
     * to std::atomic<long> once we do.
     */
    using refcount_t = long;

    class refcount_obj
    {
        public:
            refcount_obj() = default;

            void increment() noexcept;
            void increment_weak() noexcept;
            bool decrement() noexcept;
            bool decrement_weak() noexcept;
            refcount_t refs() const noexcept;
            refcount_t weak_refs() const noexcept;
            bool expired() const noexcept;

            virtual ~refcount_obj() = default;
            virtual void destroy() = 0;

        protected:
            /**
             * We're using a trick where refcount_ > 0
             * means weak_refcount_ has 1 added to it,
             * this makes it easier for weak_ptrs that
             * can't decrement the weak_refcount_ to
             * zero with shared_ptrs using this object.
             */
            refcount_t refcount_{1};
            refcount_t weak_refcount_{1};
    };
}

#endif