LazyValue.hpp

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// @formatter:off
//
// Balau core C++ library
//
// Copyright (C) 2008 Bora Software (contact@borasoftware.com)
//
// Licensed under the Boost Software License - Version 1.0 - August 17th, 2003.
// See the LICENSE file for the full license text.
//


#ifndef COM_BORA_SOFTWARE__BALAU_CONCURRENT__LAZY_VALUE
#define COM_BORA_SOFTWARE__BALAU_CONCURRENT__LAZY_VALUE

#include <atomic>
#include <functional>
#include <mutex>

namespace Balau::Concurrent {

template <typename T> class LazyValue {
    public: explicit LazyValue(std::function<void (T &)> destruct_ = std::function<void (T &)>())
        : destruct(destruct_)
        , constructed(false) {}

    public: ~LazyValue() {
        std::lock_guard<std::mutex> lock(mutex);

        if (constructed && destruct) {
            destruct(value);
        }
    }

    public: T & operator () (std::function<T ()> construct) {
        if (!constructed.load(std::memory_order_acquire)) {
            std::lock_guard<std::mutex> lock(mutex);

            if (!constructed.load(std::memory_order_relaxed)) {
                value = construct();
                constructed.store(true, std::memory_order_release);
            }
        }

        return value;
    }

    public: bool isConstructed() const {
        return constructed;
    }

    public: std::mutex & getMutex() {
        return mutex;
    }


    private: std::function<void (T &)> destruct;
    private: std::atomic_bool constructed;
    private: std::mutex mutex;
    private: T value;
};

} // namespace Balau::Concurrent

#endif // COM_BORA_SOFTWARE__BALAU_CONCURRENT__LAZY_VALUE