I have some trouble with QTcpSockets in combination with Threads.
I guess I have misunderstood the documentation regarding Threads, maybe you can explain where my mistake lies. What part should go into the run() method, and when a signal is emitted and connected to a slot on the threaded class, where is it received? In the "base", not in the run(), right? So how do i notify the "running" part that there is something it has to do? A Shared Object? How?
What I want to archive in the end is the following:
+-----------------------+
| Server |
| keeps some global |
| objects |
+--X----------------X---+
X X
+---------------X---+ +--X----------------+
| | | |
| Thread for Client | | Thread for Client |
| B | | A |
| keeps local data | | keeps local data |
+-----------X-------+ +-----------X-------+
X X
X X
+---------X----+ +--------X-----+
| Socket | | Socket |
+-------+---+--+ +----+---+-----+
^ | | ^
| | ---------------- | |
| | Network | |
| | --------------- | |
| | | | +----------------+
| | | | | |
| | | +-------+ Client A |
| | | | |
| | +---------->+----------------+
| |
| | +----------------+
| +------------------------------------->+ |
| | Client B |
+------------------------------------------+ |
+----------------+
Below added code works gives "QSocketNotifier: Socket notifiers cannot be enabled or disabled from another thread". My earlier approach (without code here) gave "QObject: Cannot create children for a parent that is in a different thread.". I also did read the Events-Threads-Objects wiki article (https://wiki.qt.io/Threads_Events_QObjects), but I guess I got something mixed up.
What do I have to change here, that client A can send data to the server, the server changes the data and passes the answer to client A and B (I will set keep-alive option to the socket in the real application, but left it out here for simplification reasons). All "clients" (their threads) have to be able to read and modify objects from the server. What is the best approach for doing this? I guess I should use signal and slots here, and autoconnection should be good enough (I am OK if all threads are notified to send out data at once, i have a reciever id in my protocol, so I can check if the message should be discarded before calling write().
server.pro:
QT += network
QT += core
HEADERS = \
server.h \
clientthread.h
SOURCES = \
main.cpp \
server.cpp \
clientthread.cpp
clietthead.h:
#ifndef CTHREAD_H
#define CHREAD_H
#include <QThread>
#include <QTcpSocket>
class ClientThread : public QThread {
Q_OBJECT
public:
ClientThread(int socketDescriptor, QObject *parent);
void run() Q_DECL_OVERRIDE;
QTcpSocket * tcpSocket;
public slots:
void slot_msg_answer();
void slot_request_msg_FromServer();
signals:
void error(QTcpSocket::SocketError socketError);
void signal_for_Server_request_msg();
private:
int socketDescriptor;
};
#endif
server.h
#ifndef SERVER_H
#define SERVER_H
#include <QTcpServer>
class Server : public QTcpServer {
Q_OBJECT
signals:
void signalFor_PT_msg_answert(QString);
public:
Server(QObject *parent = 0);
public slots:
void slot_request_msg();
protected:
void incomingConnection(qintptr socketDescriptor) Q_DECL_OVERRIDE;
private:
};
#endif
clientthread.cpp
#include "clientthread.h"
#include <QTcpSocket>
#include <QtNetwork>
ClientThread::ClientThread(int socketDescriptor, QObject *parent)
: QThread(parent), socketDescriptor(socketDescriptor) {
}
void ClientThread::slot_request_msg_FromServer() {
emit signal_for_Server_request_msg();
}
void ClientThread::run() {
tcpSocket = new QTcpSocket();
tcpSocket->setSocketOption(QAbstractSocket::KeepAliveOption, true);
if (!tcpSocket->setSocketDescriptor(socketDescriptor)) {
emit error(tcpSocket->error());
return;
}
QByteArray ba ( "foo");
tcpSocket->write(ba);
tcpSocket->flush();
exec();
}
void ClientThread::slot_msg_answer() {
QByteArray ba ("bar");
tcpSocket->write(ba);
tcpSocket->flush();
}
main.cpp
#include <QtCore>
#include "server.h"
int main(int argc, char *argv[]) {
QCoreApplication app(argc, argv);
Server server_;
if (!server_.listen(QHostAddress::Any, 1234)) {
qDebug() << "unable to start the server";
return -1;
}
return app.exec();
}
server.cpp
#include "server.h"
#include "clientthread.h"
#include <QTimer>
Server::Server(QObject *parent) : QTcpServer(parent) {
}
void Server::slot_request_msg() {
emit signalFor_PT_msg_answert("hello");
}
void Server::incomingConnection(qintptr socketDescriptor) {
ClientThread *thread = new ClientThread(socketDescriptor, this);
connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
connect(this, &Server::signalFor_PT_msg_answert, thread , &ClientThread::slot_msg_answer);
connect(thread, &ClientThread::signal_for_Server_request_msg, this, &Server::slot_request_msg);
thread->start();
QTimer *timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), thread, SLOT(slot_msg_answer()));
timer->start(2000);
}
All above code is based on Qt's threaded fortune server example, which is under bsd licence:
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