Re: [Boost-users] [asio] serial_port question

Subject: Re: [Boost-users] [asio] serial_port question
From: Robert Dailey (rcdailey_at_[hidden])
Date: 2009-08-26 11:09:22

On Tue, Aug 25, 2009 at 9:04 PM, Michael Caisse <
boost_at_[hidden]> wrote:

> Whoops ... forgot to start the read again in the completion handler.
> "Fixed" below.
>
> Michael Caisse wrote:
>
>>
>>
>>
>> void my_message_maker::read_start()
>> {
>>  serial_port.async_read_some( boost::asio::buffer( in_message,
>> MAX_MESSAGE_SIZE ),
>>                               boost::bind( &my_message_maker::read_done,
>>                                            this,
>>
>>  boost::asio::placeholders::error,
>>
>>  boost::asio::placeholders::bytes_transferred ) );
>> }
>>
>>
>> void my_message_maker::read_done( const boost::system::error_code& error,
>>                                 int bytes_transferred )
>> {
>>  if( !error )
>>  {
>>     for( int i=0; i < bytes_transferred; ++i )
>>     {
>>        if( in_message[ i ] == STX )
>>        {
>>           my_message.clear();
>>        }
>>        else if( in_message[ i ] == ETX )
>>        {
>>           make_callback( my_message );
>>        }
>>        else
>>        {
>>           my_message += in_message[ i ];
>>        }
>>
>         read_start();
>      }
>
>   }
>>  else
>>  {
>>     close_port( error );
>>  }
>> }
>
>
Ah, i see what you're saying now. I was thinking from a lower level (i.e.
that I would not call any read methods until I was notified from the
socket/serial port layer that information was ready). It's actually a good
idea to take it up to a higher level like this and validate data completion
and defragment the buffers.

Would you recommend calling read_start() from its own thread and have it
loop indefinitely? I believe this is what you originally suggested. However,
I am curious about the issues with calling read_some() and write_some() from
separate threads without using any external synchronization techniques (i.e.
mutexes). Do I have to synchronize these two calls manually or is it done
internally? I'll re-review the documentation, but I did not see anything
regarding this earlier.

Thanks for your help.