Re: Thread & Serial port

[Paul Davis <pjdavis engineering uiowa edu>]

Christophe ASSOUS wrote:

> Hello,   I would want to create three thread, each reading and writing 
> on a serial port at the same time. Is it possible ? Would you have an 
> idea on how doing the management of the serial port by the thread?   
> If you have already done it, I would be pleased you to send me 
> information or source code about this topic. (cube6_2000 yahoo fr)     
> Cordially,   Kris
>
>  
I'm actually getting ready to write something similar, but for sockets.

My plan is to create an object to wrap around the file descriptor that I 
can synchronize for reading and writing.  Then each thread can read and 
write to their hearts desire.

I use pthread_mutex_t for locking.  There are also some Glib classes for 
locking I do believe.  And you could use file locking too.  Basically, 
just make sure you own the lock when performing an operation on the file 
descriptor.

A simplified class would be something like this:

class SyncSerialPort
{
   public:
      SyncSerialPort( std::string dev )
      {
         _fd = open( dev.c_str(), O_RDWR ) ;
         throw if _fd < 0
         pthread_mutex_init( &_lock, NULL ) ;
       }

       ~SyncSerialPort()
      {
         pthread_mutex_destroy( &_lock ) ;
         close( _fd ) ;
      }

      size_t
      read( void* data, size_t size )
      {
         size_t ret ;
         pthread_mutex_lock( &_lock ) ;

         ret = read( _fd, data, size ) ;

         pthread_mutex_unlock( &_lock ) ;

         return ret ;
      }

      size_t
      write( void* data, size_t size )
      {
         size_t ret ;

         pthread_mutex_lock( &_lock ) ;

         ret = write( _fd, data, size ) ;

         pthread_mutex_unlock( &_lock ) ;

         return ret ;
      }

   private:
      int      _fd ;
      pthread_mutex_t   _lock ;
} ;

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