How to write data to TcpSocket from another thread?

mrjj

Hi
Could you not just use signal and slot ?
So when UART has data it emit signal to MyServer to actually send some reply ?
But im having hard time to understand the code as you seem to both
make a UART_Protokol and Myserver in main but at the same time
also make new one in void MyServer::read() and
a server in void UART_Protokol::ParseCommand()
so im not really sure what class should be talking to what class.

Sencis

I've tried using the signal for the recording method but nothing either fail.

It was necessary to create a new class to inherit Q_OBJECT otherwise the linker does not allow to use WiringPi for work with UART.


class Signals: public QObject
{

 Q_OBJECT

public:
    Signals();


public slots:
   void setValue();
signals:
   void event_uart();

};

Signals::Signals(){}

void Signals::setValue()
{
  emit event_uart();
}

The MyServer::write slot does not work when sending a signal.

void MyServer::incomingConnection(int socketDescriptor ) 
{
    socket = new QTcpSocket(this);

    Signals ref;

    socket->setSocketDescriptor( socketDescriptor );

    connect(socket,SIGNAL(readyRead()),this,SLOT(read())); 

    connect(socket,SIGNAL(disconnected()),this,SLOT(disconect())); 

    connect(&ref,SIGNAL(event_uart()), this,SLOT(write()));  //connected signal with UART 

    qDebug()<<socketDescriptor<<"Client connected";

    socket->write("Connection");

}

void UART_Protokol::ParseCommand()
{

   Signals ref;

  if(sp_dataString == "Start") { TransmitData = "ready"; sp_Send(TransmitData); qDebug()<<"Self-test"; }
  if(sp_dataString == "ready") qDebug()<<"Self-test";

  if (sp_dataString =="MG1")  { qDebug()<<"Start calibration..."; ref.setValue(); // send signal       }
  if (sp_dataString =="MG0")  { qDebug()<<"End calibration..."; ref.setValue();                                 }
  if (sp_dataString =="MG")   { qDebug()<<"Calibration...";                                            }
}

mrjj

Hi
I wonder about

void MyServer::incomingConnection(int socketDescriptor ) 
{
    socket = new QTcpSocket(this);

    Signals ref; // this is local object and will be deleted as soon as function ends

    socket->setSocketDescriptor( socketDescriptor );

    connect(socket,SIGNAL(readyRead()),this,SLOT(read())); 

    connect(socket,SIGNAL(disconnected()),this,SLOT(disconect())); 

    connect(&ref,SIGNAL(event_uart()), this,SLOT(write()));  //connected signal with UART 

    qDebug()<<socketDescriptor<<"Client connected";

    socket->write("Connection");

}

Since Signals ref; is gone as soon as function ends, how will it ever emit event_uart()
once data arrives ?

i was expecting something like

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    UART_Protokol Serial;
    Serial.StartProtokol( false );
   std::thread serial (&UART_Protokol::Event, Serial);  

    MyServer Server;
   connect(&Serial, UART_Protokol::ServerWrite, &Server, MyServer::write, Qt::QueuedConnection); // or similar
 
    Server.startserver();

    return a.exec();
}

and then in (and other places )
void UART_Protokol::ParseCommand()
{
// MyServer myserver; // why make a new local server when you have one in main ??
.....
  if (sp_dataString =="MG1")  emit ServerWrite("MG1");  //emit signal to server in main
.....
}

Sencis

I can't use the emit ServerWrite signal because I need UART_Protokol class inherit to the QObject class without this will be error when creating the signal slot. But i cannot inherit this class because the linker throws an error.

class UART_Protokol
{

 Q_OBJECT //If i inherit QObject to the UART_Protokol: undefined reference to `vtable for UART_Protokol'

//And without Q_OBJECT I can't use signals

signals:

  void ServerWrite (QByteArray dat);

Is this how it's gonna work? Can I use a signal from another class?

QObject::connect (&signal,&Signals::setValue, &Server,&MyServer::write, Qt::QueuedConnection);

mrjj

HI
Cant you just do
class UART_Protokol : public QObject
{
Q_OBJECT
...

ah,
undefined reference to `vtable for UART_Protokol'

thats happens often.
just inherit from QObject
then clean all of build folder
and then rebuild all.
Its a known error coming from not all is recompiled after adding QObject

Sencis

I cleaned up the entire contents of the folder and reassembled everything. Error appeared: "Class contains Q_OBJECT macro but does not inherit from QObject ":

/#ifndef PROTOKOL_OBMENA_CHEREZ_UART_H
#define PROTOKOL_OBMENA_CHEREZ_UART_H
#include <QString>
#include <thread>
#include <myserver.h>
#include <QObject>

class UART_Protokol 
{

 Q_OBJECT

If inherit a class from QObject how in other example, other errors occur:

#ifndef PROTOKOL_OBMENA_CHEREZ_UART_H
#define PROTOKOL_OBMENA_CHEREZ_UART_H
#include <QString>
#include <thread>
#include <myserver.h>
#include <QObject>

class UART_Protokol : public QObject
{

 Q_OBJECT

use of deleted function ‘UART_Protokol::UART_Protokol(const UART_Protokol&)’
: _M_head_impl(std::forward<_UHead>(__h)) { }

‘QObject::QObject(const QObject&)’ is private within this context

use of deleted function ‘QObject::QObject(const QObject&)’
class UART_Protokol : public QObject
^~~~~~~~~~~~~
^
no matching function for call to ‘std::tuple<std::_Mem_fn<void (UART_Protokol::)()>, UART_Protokol>::tuple(std::_Mem_fn<void (UART_Protokol::)()>, UART_Protokol&)’
: _M_bound(std::forward<_Tp>(__f), std::forward<_Up>(__args)...)
^

SGaist

Hi,

That means that you are trying to copy an instance of your object which is not possible with QObject based classes.

See here for more information.

Sencis

If I inherit the class :

class UART_Protokol : public QObject
{

    Q_OBJECT

and comment on a thread, everything is going without errors:

// std::thread serial (&UART_Protokol::Event, Serial); 

// serial.detach();

even connecting signal to slot, build is fine:

QObject::connect (&Serial,&UART_Protokol::ServerWrite, &Server,&MyServer::write, Qt::QueuedConnection);

That's just it I need to check the UART buffer for reading messages.

SGaist

Did you read the document I linked regarding copying QObject based classes ?

Sencis

Thank you all for your help, the signals really work fine and now i can easily pass the calibration data of the magnetometer! The truth is everything works in one thread with a timer but the delay is not big.