sync_cell/queue/blocking_queue.hpp at master · mematrix/sync_cell · GitHub

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///
/// @file  blocking_queue.hpp
/// @brief An adapter queue that adds blocking dequeue operation for the inner
/// non-blocking queue. If the inner queue supports blocking dequeue, the adapter
/// just forwards the call.
///

#ifndef SYNC_CELL_BLOCKING_QUEUE_HPP
#define SYNC_CELL_BLOCKING_QUEUE_HPP

#include <condition_variable>
#include <mutex>
#include <type_traits>


namespace sc {

namespace impl {

template<typename T>
class HasDequeue
{
    using yes_type = char;
    using no_type = int;
    static_assert(sizeof(yes_type) != sizeof(no_type));

    // Only need the declaration, add an implementation to suppress the IDE warning.
    template<typename C>
    [[maybe_unused]] static yes_type test(decltype(&C::dequeue)) { return {}; }

    template<typename>
    [[maybe_unused]] static no_type test(...) { return {}; }

public:
    static constexpr bool value = sizeof(test<T>(nullptr)) == sizeof(yes_type);
};

}

template<typename Queue, bool = impl::HasDequeue<Queue>::value>
class BlockingQueue
{
    template<typename>
    inline static constexpr bool dependent_false_v = false;

public:
    using value_type = typename Queue::value_type;
    using reference = typename Queue::reference;
    using const_reference = typename Queue::reference;

    template<typename... Args>
    explicit BlockingQueue(Args &&... args) noexcept(std::is_nothrow_constructible_v<Queue, Args...>)
            : queue_(std::forward<Args>(args)...)
    {
    }

    BlockingQueue(const BlockingQueue &) noexcept(std::is_nothrow_copy_constructible_v<Queue>) = default;

    BlockingQueue(BlockingQueue &&) noexcept(std::is_nothrow_move_assignable_v<Queue>) = default;

    BlockingQueue &operator=(const BlockingQueue &) noexcept(std::is_nothrow_copy_assignable_v<Queue>) = default;

    BlockingQueue &operator=(BlockingQueue &&) noexcept(std::is_nothrow_move_assignable_v<Queue>) = default;

    template<typename V>
    void enqueue(V &&v)
    {
        if constexpr(std::is_same_v<value_type, std::remove_cvref_t<V>>) {
            queue_.enqueue(std::forward<V>(v));
        } else if constexpr(std::is_constructible_v<V, value_type>) {
            queue_.enqueue(value_type(std::forward<V>(v)));
        } else {
            static_assert(dependent_false_v<V>, "Type is not expected.");
        }

        cond_var_.notify_all();
    }

    auto try_dequeue()
    {
        return queue_.try_dequeue();
    }

    value_type dequeue()
    {
        static_assert(std::is_convertible_v<decltype(*(queue_.try_dequeue())), value_type>);

        while (true) {
            auto v = queue_.try_dequeue();
            if (v) {
                return *std::move(v);
            }

            std::unique_lock lock(mtx_);
            cond_var_.wait(lock);
        }
    }

private:
    Queue queue_;

    std::mutex mtx_;
    std::condition_variable cond_var_;
};

template<typename Queue>
class BlockingQueue<Queue, true>
{
    template<typename>
    inline static constexpr bool dependent_false_v = false;

public:
    using value_type = typename Queue::value_type;
    using reference = typename Queue::reference;
    using const_reference = typename Queue::reference;

    template<typename... Args>
    explicit BlockingQueue(Args &&... args) noexcept(std::is_nothrow_constructible_v<Queue, Args...>)
            : queue_(std::forward<Args>(args)...)
    {
    }

    BlockingQueue(const BlockingQueue &) noexcept(std::is_nothrow_copy_constructible_v<Queue>) = default;

    BlockingQueue(BlockingQueue &&) noexcept(std::is_nothrow_move_assignable_v<Queue>) = default;

    BlockingQueue &operator=(const BlockingQueue &) noexcept(std::is_nothrow_copy_assignable_v<Queue>) = default;

    BlockingQueue &operator=(BlockingQueue &&) noexcept(std::is_nothrow_move_assignable_v<Queue>) = default;

    template<typename V>
    void enqueue(V &&v)
    {
        if constexpr(std::is_same_v<value_type, std::remove_cvref_t<V>>) {
            queue_.enqueue(std::forward<V>(v));
        } else if constexpr(std::is_constructible_v<V, value_type>) {
            queue_.enqueue(value_type(std::forward<V>(v)));
        } else {
            static_assert(dependent_false_v<V>, "Type is not expected.");
        }
    }

    auto try_dequeue()
    {
        return queue_.try_dequeue();
    }

    auto dequeue()
    {
        return queue_.dequeue();
    }

private:
    Queue queue_;
};

}

#endif //SYNC_CELL_BLOCKING_QUEUE_HPP