jthread.hpp

// -----------------------------------------------------
// cooperative interruptable and joining thread:
// -----------------------------------------------------
#ifndef JTHREAD_HPP
#define JTHREAD_HPP

#include "stop_token.hpp"
#include <thread>
#include <future>
#include <type_traits>
#include <functional>  // for invoke()
#include <iostream>    // for debugging output

namespace std {

//*****************************************
//* class jthread
//* - joining std::thread with signaling stop/end support
//*****************************************
class jthread
{
  public:
    //*****************************************
    //* standardized API:
    //*****************************************
    // - cover full API of std::thread
    //   to be able to switch from std::thread to std::jthread

    // types are those from std::thread:
    using id = ::std::thread::id;
    using native_handle_type = ::std::thread::native_handle_type;

    // construct/copy/destroy:
    jthread() noexcept;
    //template <typename F, typename... Args> explicit jthread(F&& f, Args&&... args);
    // THE constructor that starts the thread:
    // - NOTE: does SFINAE out copy constructor semantics
    template <typename Callable, typename... Args,
              typename = ::std::enable_if_t<!::std::is_same_v<::std::decay_t<Callable>, jthread>>>
    explicit jthread(Callable&& cb, Args&&... args);
    ~jthread();

    jthread(const jthread&) = delete;
    jthread(jthread&&) noexcept = default;
    jthread& operator=(const jthread&) = delete;
    jthread& operator=(jthread&&) noexcept;

    // members:
    void swap(jthread&) noexcept;
    bool joinable() const noexcept;
    void join();
    void detach();

    id get_id() const noexcept;
    native_handle_type native_handle();

    // static members:
    static unsigned hardware_concurrency() noexcept {
      return ::std::thread::hardware_concurrency();
    };

    //*****************************************
    // - supplementary API:
    //   - for the calling thread:
    [[nodiscard]] stop_source get_stop_source() noexcept;
    [[nodiscard]] stop_token get_stop_token() const noexcept;
    bool request_stop() noexcept {
      return get_stop_source().request_stop();
    }


  //*****************************************
  //* implementation:
  //*****************************************

  private:
    //*** API for the starting thread:
    stop_source _stopSource;                   // stop_source for started thread
    ::std::thread _thread{};                   // started thread (if any)
};


//**********************************************************************

//*****************************************
//* implementation of class jthread
//*****************************************

// default constructor:
inline jthread::jthread() noexcept
 : _stopSource{nostopstate} {
}

// THE constructor that starts the thread:
// - NOTE: declaration does SFINAE out copy constructor semantics
template <typename Callable, typename... Args,
          typename >
inline jthread::jthread(Callable&& cb, Args&&... args)
 : _stopSource{},                             // initialize stop_source
   _thread{[] (stop_token st, auto&& cb, auto&&... args) {   // called lambda in the thread
                 // perform tasks of the thread:
                 if constexpr(std::is_invocable_v<Callable, stop_token, Args...>) {
                   // pass the stop_token as first argument to the started thread:
                   ::std::invoke(::std::forward<decltype(cb)>(cb),
                                 std::move(st),
                                 ::std::forward<decltype(args)>(args)...);
                 }
                 else {
                   // started thread does not expect a stop token:
                   ::std::invoke(::std::forward<decltype(cb)>(cb),
                                 ::std::forward<decltype(args)>(args)...);
                 }
               },
               _stopSource.get_token(),   // not captured due to possible races if immediately set
               ::std::forward<Callable>(cb),  // pass callable
               ::std::forward<Args>(args)...  // pass arguments for callable
           }
{
}

// move assignment operator:
inline jthread& jthread::operator=(jthread&& t) noexcept {
  if (joinable()) {   // if not joined/detached, signal stop and wait for end:
    request_stop();
    join();
  }

  _thread = std::move(t._thread);
  _stopSource = std::move(t._stopSource);
  return *this;
}

// destructor:
inline jthread::~jthread() {
  if (joinable()) {   // if not joined/detached, signal stop and wait for end:
    request_stop();
    join();
  }
}


// others:
inline bool jthread::joinable() const noexcept {
  return _thread.joinable();
}
inline void jthread::join() {
  _thread.join();
}
inline void jthread::detach() {
  _thread.detach();
}
inline typename jthread::id jthread::get_id() const noexcept {
  return _thread.get_id();
}
inline typename jthread::native_handle_type jthread::native_handle() {
  return _thread.native_handle();
}

inline stop_source jthread::get_stop_source() noexcept {
  return _stopSource;
}
inline stop_token jthread::get_stop_token() const noexcept {
  return _stopSource.get_token();
}

inline void jthread::swap(jthread& t) noexcept {
    std::swap(_stopSource, t._stopSource);
    std::swap(_thread, t._thread);
}


} // std

#endif // JTHREAD_HPP