#### co_spawn (5 of 6 overloads)

Spawn a new coroutined-based thread of execution.

    template<
        typename Executor,
        typename F,
        typename CompletionToken = DEFAULT>
    DEDUCED co_spawn(
        const Executor & ex,
        F && f,
        CompletionToken && token = DEFAULT,
        constraint_t< is_executor< Executor >::value||execution::is_executor< Executor >::value >  = 0);

###### Parameters

ex

  The executor that will be used to schedule the new thread of execution.

f

  A nullary function object with a return type of the form `asio::awaitable<R,E>` that will be used as the coroutine's entry point.

token

  The completion token that will handle the notification that the thread of execution has completed. If `R` is `void`, the function signature of the completion handler must be:

    void handler(std::exception_ptr);

Otherwise, the function signature of the completion handler must be:

    void handler(std::exception_ptr, R);

###### Completion Signature

    void(std::exception_ptr, R)

where `R` is the first template argument to the `awaitable` returned by the supplied function object `F:`

    asio::awaitable<R, AwaitableExecutor> F()

###### Example

    asio::awaitable<std::size_t> echo(tcp::socket socket)
    {
      std::size_t bytes_transferred = 0;

      try
      {
        char data[1024];
        for (;;)
        {
          std::size_t n = co_await socket.async_read_some(
              asio::buffer(data), asio::use_awaitable);

          co_await asio::async_write(socket,
              asio::buffer(data, n), asio::use_awaitable);

          bytes_transferred += n;
        }
      }
      catch (const std::exception&)
      {
      }

      co_return bytes_transferred;
    }

    // ...

    asio::co_spawn(my_executor,
      [socket = std::move(my_tcp_socket)]() mutable
        -> asio::awaitable<void>
      {
        try
        {
          char data[1024];
          for (;;)
          {
            std::size_t n = co_await socket.async_read_some(
                asio::buffer(data), asio::use_awaitable);

            co_await asio::async_write(socket,
                asio::buffer(data, n), asio::use_awaitable);
          }
        }
        catch (const std::exception& e)
        {
          std::cerr << "Exception: " << e.what() << "\n";
        }
      }, asio::detached);

###### Per-Operation Cancellation

The new thread of execution is created with a cancellation state that supports `cancellation_type::terminal` values only. To change the cancellation state, call `this_coro::reset_cancellation_state`.