coroutine.hh

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 * property including but not limited to intellectual property relating
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 * Authors: Giacomo Travaglini
 */

#ifndef __BASE_COROUTINE_HH__
#define __BASE_COROUTINE_HH__

#include <functional>
#include <stack>

#include "base/fiber.hh"

namespace m5
{

template <typename Arg, typename Ret>
class Coroutine : public Fiber
{

    // This empty struct type is meant to replace coroutine channels
    // in case the channel should be void (Coroutine template parameters
    // are void. (See following ArgChannel, RetChannel typedef)
    struct Empty {};
    using ArgChannel = typename std::conditional<
        std::is_same<Arg, void>::value, Empty, std::stack<Arg>>::type;

    using RetChannel = typename std::conditional<
        std::is_same<Ret, void>::value, Empty, std::stack<Ret>>::type;

  public:
    class CallerType
    {
        friend class Coroutine;
      protected:
        CallerType(Coroutine& _coro) : coro(_coro), callerFiber(nullptr) {}

      public:
        template <typename T = Ret>
        CallerType&
        operator()(typename std::enable_if<
                   !std::is_same<T, void>::value, T>::type param)
        {
            retChannel.push(param);
            callerFiber->run();
            return *this;
        }

        template <typename T = Ret>
        typename std::enable_if<std::is_same<T, void>::value,
                                CallerType>::type&
        operator()()
        {
            callerFiber->run();
            return *this;
        }

        template <typename T = Arg>
        typename std::enable_if<!std::is_same<T, void>::value, T>::type
        get()
        {
            auto& args_channel = coro.argsChannel;
            while (args_channel.empty()) {
                callerFiber->run();
            }

            auto ret = args_channel.top();
            args_channel.pop();
            return ret;
        }

      private:
        Coroutine& coro;
        Fiber* callerFiber;
        RetChannel retChannel;
    };

    Coroutine() = delete;
    Coroutine(const Coroutine& rhs) = delete;
    Coroutine& operator=(const Coroutine& rhs) = delete;

    Coroutine(std::function<void(CallerType&)> f, bool run_coroutine = true)
      : Fiber(), task(f), caller(*this)
    {
        // When desired, run the Coroutine after it is created
        if (run_coroutine)
            this->call();
    }

    virtual ~Coroutine() {}

  public:
    template <typename T = Arg>
    Coroutine&
    operator()(typename std::enable_if<
               !std::is_same<T, void>::value, T>::type param)
    {
        argsChannel.push(param);
        this->call();
        return *this;
    }

    template <typename T = Arg>
    typename std::enable_if<std::is_same<T, void>::value, Coroutine>::type&
    operator()()
    {
        this->call();
        return *this;
    }

    template <typename T = Ret>
    typename std::enable_if<!std::is_same<T, void>::value, T>::type
    get()
    {
        auto& ret_channel = caller.retChannel;
        while (ret_channel.empty()) {
            this->call();
        }

        auto ret = ret_channel.top();
        ret_channel.pop();
        return ret;
    }

    operator bool() const { return !this->finished(); }

  private:
    void main() override { this->task(caller); }

    void
    call()
    {
        caller.callerFiber = currentFiber();
        run();
    }

  private:
    ArgChannel argsChannel;

    std::function<void(CallerType&)> task;

    CallerType caller;
};

} //namespace m5

#endif // __BASE_COROUTINE_HH__