text: //
  // detail/io_uring_socket_recv_op.hpp
  // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  //
  // Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
  //
  // Distributed under the Boost Software License, Version 1.0. (See accompanying
  // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  //
  
  #ifndef ASIO_DETAIL_IO_URING_SOCKET_RECV_OP_HPP
  #define ASIO_DETAIL_IO_URING_SOCKET_RECV_OP_HPP
  
  #if defined(_MSC_VER) && (_MSC_VER >= 1200)
  # pragma once
  #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
  
  #include "asio/detail/config.hpp"
  
  #if defined(ASIO_HAS_IO_URING)
  
  #include "asio/detail/bind_handler.hpp"
  #include "asio/detail/buffer_sequence_adapter.hpp"
  #include "asio/detail/socket_ops.hpp"
  #include "asio/detail/fenced_block.hpp"
  #include "asio/detail/handler_work.hpp"
  #include "asio/detail/io_uring_operation.hpp"
  #include "asio/detail/memory.hpp"
  
  #include "asio/detail/push_options.hpp"
  
  namespace asio {
  namespace detail {
  
  template <typename MutableBufferSequence>
  class io_uring_socket_recv_op_base : public io_uring_operation
  {
  public:
    io_uring_socket_recv_op_base(const asio::error_code& success_ec,
        socket_type socket, socket_ops::state_type state,
        const MutableBufferSequence& buffers,
        socket_base::message_flags flags, func_type complete_func)
      : io_uring_operation(success_ec,
          &io_uring_socket_recv_op_base::do_prepare,
          &io_uring_socket_recv_op_base::do_perform, complete_func),
        socket_(socket),
        state_(state),
        buffers_(buffers),
        flags_(flags),
        bufs_(buffers),
        msghdr_()
    {
      msghdr_.msg_iov = bufs_.buffers();
      msghdr_.msg_iovlen = static_cast<int>(bufs_.count());
    }
  
    static void do_prepare(io_uring_operation* base, ::io_uring_sqe* sqe)
    {
      io_uring_socket_recv_op_base* o(
          static_cast<io_uring_socket_recv_op_base*>(base));
  
      if ((o->state_ & socket_ops::internal_non_blocking) != 0)
      {
        bool except_op = (o->flags_ & socket_base::message_out_of_band) != 0;
        ::io_uring_prep_poll_add(sqe, o->socket_, except_op ? POLLPRI : POLLIN);
      }
      else if (o->bufs_.is_single_buffer
          && o->bufs_.is_registered_buffer && o->flags_ == 0)
      {
        ::io_uring_prep_read_fixed(sqe, o->socket_,
            o->bufs_.buffers()->iov_base, o->bufs_.buffers()->iov_len,
            0, o->bufs_.registered_id().native_handle());
      }
      else
      {
        ::io_uring_prep_recvmsg(sqe, o->socket_, &o->msghdr_, o->flags_);
      }
    }
  
    static bool do_perform(io_uring_operation* base, bool after_completion)
    {
      io_uring_socket_recv_op_base* o(
          static_cast<io_uring_socket_recv_op_base*>(base));
  
      if ((o->state_ & socket_ops::internal_non_blocking) != 0)
      {
        bool except_op = (o->flags_ & socket_base::message_out_of_band) != 0;
        if (after_completion || !except_op)
        {
          if (o->bufs_.is_single_buffer)
          {
            return socket_ops::non_blocking_recv1(o->socket_,
                o->bufs_.first(o->buffers_).data(),
                o->bufs_.first(o->buffers_).size(), o->flags_,
                (o->state_ & socket_ops::stream_oriented) != 0,
                o->ec_, o->bytes_transferred_);
          }
          else
          {
            return socket_ops::non_blocking_recv(o->socket_,
                o->bufs_.buffers(), o->bufs_.count(), o->flags_,
                (o->state_ & socket_ops::stream_oriented) != 0,
                o->ec_, o->bytes_transferred_);
          }
        }
      }
      else if (after_completion)
      {
        if (!o->ec_ && o->bytes_transferred_ == 0)
          if ((o->state_ & socket_ops::stream_oriented) != 0)
            o->ec_ = asio::error::eof;
      }
  
      if (o->ec_ && o->ec_ == asio::error::would_block)
      {
        o->state_ |= socket_ops::internal_non_blocking;
        return false;
      }
  
      return after_completion;
    }
  
  private:
    socket_type socket_;
    socket_ops::state_type state_;
    MutableBufferSequence buffers_;
    socket_base::message_flags flags_;
    buffer_sequence_adapter<asio::mutable_buffer,
        MutableBufferSequence> bufs_;
    msghdr msghdr_;
  };
  
  template <typename MutableBufferSequence, typename Handler, typename IoExecutor>
  class io_uring_socket_recv_op
    : public io_uring_socket_recv_op_base<MutableBufferSequence>
  {
  public:
    ASIO_DEFINE_HANDLER_PTR(io_uring_socket_recv_op);
  
    io_uring_socket_recv_op(const asio::error_code& success_ec,
        int socket, socket_ops::state_type state,
        const MutableBufferSequence& buffers, socket_base::message_flags flags,
        Handler& handler, const IoExecutor& io_ex)
      : io_uring_socket_recv_op_base<MutableBufferSequence>(success_ec,
          socket, state, buffers, flags, &io_uring_socket_recv_op::do_complete),
        handler_(ASIO_MOVE_CAST(Handler)(handler)),
        work_(handler_, io_ex)
    {
    }
  
    static void do_complete(void* owner, operation* base,
        const asio::error_code& /*ec*/,
        std::size_t /*bytes_transferred*/)
    {
      // Take ownership of the handler object.
      io_uring_socket_recv_op* o
        (static_cast<io_uring_socket_recv_op*>(base));
      ptr p = { asio::detail::addressof(o->handler_), o, o };
  
      ASIO_HANDLER_COMPLETION((*o));
  
      // Take ownership of the operation's outstanding work.
      handler_work<Handler, IoExecutor> w(
          ASIO_MOVE_CAST2(handler_work<Handler, IoExecutor>)(
            o->work_));
  
      // Make a copy of the handler so that the memory can be deallocated before
      // the upcall is made. Even if we're not about to make an upcall, a
      // sub-object of the handler may be the true owner of the memory associated
      // with the handler. Consequently, a local copy of the handler is required
      // to ensure that any owning sub-object remains valid until after we have
      // deallocated the memory here.
      detail::binder2<Handler, asio::error_code, std::size_t>
        handler(o->handler_, o->ec_, o->bytes_transferred_);
      p.h = asio::detail::addressof(handler.handler_);
      p.reset();
  
      // Make the upcall if required.
      if (owner)
      {
        fenced_block b(fenced_block::half);
        ASIO_HANDLER_INVOCATION_BEGIN((handler.arg1_, handler.arg2_));
        w.complete(handler, handler.handler_);
        ASIO_HANDLER_INVOCATION_END;
      }
    }
  
  private:
    Handler handler_;
    handler_work<Handler, IoExecutor> work_;
  };
  
  } // namespace detail
  } // namespace asio
  
  #include "asio/detail/pop_options.hpp"
  
  #endif // defined(ASIO_HAS_IO_URING)
  
  #endif // ASIO_DETAIL_IO_URING_SOCKET_RECV_OP_HPP
  