threads for tcp communication

Question

My question is about usage of threads. Im making an application that connects to a device over TCP/IP. Im using boost::asio lib. I have decided to use a read or listening thread and a write thread for listening and writing to the device respectively. My confusion is should the function creating the socket that handles the communication also be a thread. Thanks :)

Answer 1

In my client class, I create 2 worker threads to handle sending and receiving messages which are used for multiple connections to multiple servers. The thread that creates those 2 worker threads happens to be the user interface thread. This is what my code looks like:

// Create the resolver and query objects to resolve the host name in serverPath to an ip address.
boost::asio::ip::tcp::resolver resolver(*IOService);
boost::asio::ip::tcp::resolver::query query(serverPath, port);
boost::asio::ip::tcp::resolver::iterator EndpointIterator = resolver.resolve(query);
// Set up an SSL context.
boost::asio::ssl::context ctx(*IOService, boost::asio::ssl::context::tlsv1_client);
// Specify to not verify the server certificiate right now.
ctx.set_verify_mode(boost::asio::ssl::context::verify_none);
// Init the socket object used to initially communicate with the server.
pSocket = new boost::asio::ssl::stream<boost::asio::ip::tcp::socket>(*IOService, ctx);
//
// The thread we are on now, is most likely the user interface thread.  Create a thread to handle all incoming socket work messages.
if (!RcvThreadCreated)
{
   WorkerThreads.create_thread(boost::bind(&SSLSocket::RcvWorkerThread, this));
   RcvThreadCreated = true;
   WorkerThreads.create_thread(boost::bind(&SSLSocket::SendWorkerThread, this));
 }
 // Try to connect to the server.  Note - add timeout logic at some point.
 boost::asio::async_connect(pSocket->lowest_layer(), EndpointIterator,
    boost::bind(&SSLSocket::HandleConnect, this, boost::asio::placeholders::error));

The worker threads handle all socket I/O. It depends on what you are doing, but the 2 worker threads for servicing the socket will need to be created from another thread. That other thread can be the user interface thread or main thread if you want since it will be returning pretty quickly. If you have multiple connections to servers or clients, then It is up to you to decide whether or not you want more than one set of threads to service them.

Answer 2

That depends on whether you want to read and write at the same time. In that case you would need one thread for reading and one for writing, but you would have to properly synchronize those in case both streams to and from the device have something to do with each other (what they probably do). However, talking to a device sounds to me like a task where you establish a connection, send some request, wait for and read the answer, send another request, wait for and read the next answer, etc. In that case using just one thread is sufficient and makes your life a lot easier.