Experiencing timeouts after connecting to 20 different servers using QTcpSocket - c++

Question

I've been experiencing a weird problem using QTcpSocket, I've searched the web but can't find anybody else with the same problem.
I have two bare-bones applications, one client and one server, if I run them both on my local machine the client successfully makes all 50 connections to the server.
If I run the server on another computer connected to the network (let's say: 10.1.1.1) it will again connect every time without a problem.
Now, if I change the server's main.cpp to initialise multiple servers under different ports (8001 to 8050), and change the client to make one connection to each server. With both running locally it still works fine.
int main(int argc, char** argv) {
QCoreApplication app(argc, argv);
for (int i = 8001; i <= 8050; ++i) {
Server server(i);
return app.exec();
}
}
But, if I put the server on 10.1.1.1 and try it again then I connect to the first 20 without a problem, but then it hangs for a while (anywhere upwards of 5 seconds) before connecting to the next 20, and so on until all are connected.
As a final test, I put an instance of the server on another machine (10.1.1.2) and created 15 instances of a server on each machine and tried to connect to both I experienced the same problem. All 15 of the first machine connected fine, as did the next 5 of the 2nd machine before it hung until eventually connecting to the last 10.
This is on Qt version 4.7.2. And I've experienced this problem on Fedora 17, Windows 7 but not Scientific Linux 6.
The code for the client/server is included below, I removed all the includes to save some vertical space:
Client
client.h
class Client: public QObject {
Q_OBJECT
public:
Client(QObject* parent = 0);
~Client();
void start(QString address, quint16 port);
public slots:
void startTransfer();
void disconnect() { qDebug("disconnect"); }
private:
QTcpSocket client;
};
client.cpp
Client::Client(QObject* parent): QObject(parent) {
connect(&client, SIGNAL(connected()), this, SLOT(startTransfer()));
connect(&client, SIGNAL(disconnected()), this, SLOT(disconnect()));
}
Client::~Client() {
client.close();
}
void Client::start(QString address, quint16 port) {
QHostAddress addr(address);
qDebug(QString("connecting to %1:%2").arg(address, QString::number(port)).toLocal8Bit().constData());
client.connectToHost(addr, port);
}
void Client::startTransfer() {
qDebug("connected");
client.write("Hello, world", 13);
}
main.cpp
int main(int argc, char** argv) {
QCoreApplication app(argc, argv);
for (int i = 0; i < 50; i++) {
Client *client = new Client;
client->start("192.168.0.1", 8888);
}
return app.exec();
}
Server
server.h
class Server: public QObject {
Q_OBJECT
public:
Server(int port = 8888, QObject * parent = 0);
~Server();
public slots:
void acceptConnection();
void startRead();
private:
QTcpServer server;
QList<QTcpSocket *> clients;
};
server.cpp
Server::Server(int port, QObject* parent): QObject(parent) {
qDebug(qPrintable("new server instance on port " + QString::number(port)));
connect(&server, SIGNAL(newConnection()), this, SLOT(acceptConnection()));
server.listen(QHostAddress::Any, port);
}
Server::~Server() {
server.close();
}
void Server::acceptConnection() {
QTcpSocket *client = server.nextPendingConnection();
clients.append(client);
connect(client, SIGNAL(readyRead()), this, SLOT(startRead()));
}
void Server::startRead() {
QTcpSocket *client = dynamic_cast<QTcpSocket *>(sender());
char buffer[1024] = {0};
client->read(buffer, client->bytesAvailable());
QString response = QString("%2 on server %3").arg(buffer, QString::number(server.serverPort()));
std::cout << qPrintable(response) << std::endl;
client->close();
}
main.cpp
int main(int argc, char** argv) {
QCoreApplication app(argc, argv);
Server server;
return app.exec();
}