#### posix::basic_descriptor::async_wait

Asynchronously wait for the descriptor to become ready to read, ready to write, or to have pending error conditions.

    template<
        typename WaitHandler = DEFAULT>
    DEDUCED async_wait(
        wait_type w,
        WaitHandler && handler = DEFAULT);

This function is used to perform an asynchronous wait for a descriptor to enter a ready to read, write or error condition state.

###### Parameters

w

  Specifies the desired descriptor state.

handler

  The handler to be called when the wait operation completes. Copies will be made of the handler as required. The function signature of the handler must be:

      void handler(
        const asio::error_code& error // Result of operation
      );

  Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function. On immediate completion, invocation of the handler will be performed in a manner equivalent to using `post`.

###### Example

    void wait_handler(const asio::error_code& error)
    {
      if (!error)
      {
        // Wait succeeded.
      }
    }

    ...

    asio::posix::stream_descriptor descriptor(my_context);
    ...
    descriptor.async_wait(
        asio::posix::stream_descriptor::wait_read,
        wait_handler);