Messages

1

Network / sf::SocketTCP.Send() & sf::SocketTCP.Receive() Threadsaf

« on: March 19, 2010, 04:51:14 pm »

The question is not why using Send and Receive on the same Socket : Everybody (As far as I know) use this.
The real question is why could you want to Receive and Send at the same time ?

The original poster and I don't necessarily want to Receive and Send at the same time, and the original poster pointed out that when he tried to protect them with a mutex he ran into a deadlock. This is because the Receive function was a blocking call, so if you lock a mutex before the blocking call and then the server never sends anything (let's say it's waiting for clients to send it information before it relays information down), you'll hit a deadlock on the mutex.

As with my previous post, I believe the best way to approach this is by using a non-blocking socket. However, I'm not a network coding expert and I don't know if a non-blocking socket is going to cause other problems that I'm not aware of at present.

2

Network / sf::SocketTCP.Send() & sf::SocketTCP.Receive() Threadsaf

« on: March 19, 2010, 04:18:26 pm »

The reason that I want to Send and Receive on the same socket is simplicity of code. If I can't Send and Receive on the same socket, that means each client needs to create two sockets to connect to the server and the server needs two sockets per client.

Anyway, I seem to have come to a simple solution by using SetBlocking(false) on the socket. This prevents the Receive call from causing a deadlock, and allows me to use a Mutex to protect the sf::Socket object. I hope this doesn't cause other problems, but for now it works. Here is the code, for anyone's benefit and/or feedback:

Code: [Select]


// netclient.h

// Note: I also include a project .h which uses namespace std
#include <SFML/Network.hpp>
#include <SFML/System.hpp>

class NetClient
{
public:
NetClient();
virtual ~NetClient();

bool ConnectToServer();

bool SendMessage(string message);

sf::SocketTCP   m_Socket;
sf::Mutex       m_SocketMutex;

protected:
sf::Thread    * m_pThread;
};


Code: [Select]


// netclient.cpp

#include "netclient.h"
#include <iostream>

NetClient::NetClient() : m_pThread(NULL)
{
}

NetClient::~NetClient()
{
if (this->m_Socket.IsValid())
{
this->m_SocketMutex.Lock();
this->m_Socket.Close();
this->m_SocketMutex.Unlock();
}
if (this->m_pThread != NULL)
{
this->m_pThread->Wait();
delete this->m_pThread;
}
}

void Receiver(void* UserData)
{
NetClient * netClient = static_cast<NetClient*>(UserData);

bool keepGoing = true;
while (keepGoing)
{
sf::Socket::Status status;
sf::Packet packet;
netClient->m_SocketMutex.Lock();
status = netClient->m_Socket.Receive(packet);
netClient->m_SocketMutex.Unlock();

if (status == sf::Socket::Disconnected)
{
keepGoing = false;
}
else if (status == sf::Socket::Error)
{
cout << "Encountered an error reading from socket.\n" << endl;
keepGoing = false;
}
else if (status == sf::Socket::Done)
{
string message;
packet >> message;
cout << "Server says : \"" << message << "\"" << endl;
}
}
}

bool NetClient::ConnectToServer()
{
const int Port = 2839;

// Ask for server address
sf::IPAddress ServerAddress;
do
{
cout << "Type the address or name of the server to connect to : ";
cin  >> ServerAddress;
}
while (!ServerAddress.IsValid());
cin.ignore(10000, '\n');

// Connect to the server
if (this->m_Socket.Connect(Port, ServerAddress) != sf::Socket::Done)
return false;

this->m_Socket.SetBlocking(false);

this->m_pThread = new sf::Thread(&Receiver, this);
thus->m_pThread->Launch();

return true;
}

bool NetClient::SendMessage(string message)
{
if (this->m_Socket.IsValid() == false)
{
cout << "Error: Can't send network message. Socket is invalid." << endl;
return false;
}

sf::Packet packet;
packet << message;
this->m_SocketMutex.Lock();
this->m_Socket.Send(packet);
this->m_SocketMutex.Unlock();
return true;
}


3

Network / sf::SocketTCP.Send() & sf::SocketTCP.Receive() Threadsaf

« on: March 19, 2010, 01:07:56 am »

I had the same question today.

Has anyone determined whether SFML's SocketTCP class is thread-safe, at least with regard to Send and Receive?

If not, has anyone made any code modifications that they could share?

P.S. Laurent: I like SFML a lot!