[Boost-users] [asio] thread-safe async_write with streambuf

Subject: [Boost-users] [asio] thread-safe async_write with streambuf
From: Rutger ter Borg (rutger_at_[hidden])
Date: 2009-06-04 03:42:10

Hi all, 

I'm looking into thread-safe writing of data using Asio, using a streambuf. 
My current implementation boils down to something like the following.

// posting Something from >1 thread(s)
void async_send( Something s ) {
  m_strand.post( async_send_something(s) );
}

// Serialized execution
// Protects resources socket and streambuf
void async_send_something( Something s) {
  std::ostream os( &m_streambuf );
  os << s << std::flush;
  asio::async_write( m_socket, m_streambuf, transfer_all(), bind( 
async_complete ) );
}

void async_complete( error e ) {
}

My main confusion is on how to do this with a streambuf. What happens 
between async_write and the completion handler? It could be that 
async_send_something is called from one thread before a completion handler 
of an earlier operation finishes in another thread, and in that case, I'm 
not sure if it is defined what happens with the streambuf.

For the situation sketched above, I couldn't find guarantees around the 
access pattern of other io_service threads, so my question would be if the 
implementation above is really thread-safe, and if not, how to best achieve 
that.

Thanks,
Kind regards,

Rutger