coroutine.hh

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#ifndef __BASE_COROUTINE_HH__
#define __BASE_COROUTINE_HH__
 
#include <functional>
#include <stack>
 
#include "base/compiler.hh"
#include "base/fiber.hh"
 
namespace gem5
{

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_t<
        std::is_same_v<Arg, void>, Empty, std::stack<Arg>>;
 
    using RetChannel = typename std::conditional_t<
        std::is_same_v<Ret, void>, Empty, std::stack<Ret>>;
 
  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_t<
                   !std::is_same_v<T, void>, T> param)
        {
            retChannel.push(param);
            callerFiber->run();
            return *this;
        }

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

        template <typename T = Arg>
        typename std::enable_if_t<!std::is_same_v<T, void>, T>
        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; // end of api_coroutine

    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_t<!std::is_same_v<T, void>, T> param)
    {
        argsChannel.push(param);
        this->call();
        return *this;
    }

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

    template <typename T = Ret>
    typename std::enable_if_t<!std::is_same_v<T, void>, T>
    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 gem5
 
#endif // __BASE_COROUTINE_HH__