Im aware the I cannot communicate with QTcpSocket between threads but I cannot find what Im doing wrong.
As soon as I send data emitting signal to QTcpSocket which is in the other thread, QSocketNotifier should disable itself to let QTcpSocket read data. Because I get above error it will not get disabled and readyRead() signal wont be emitted.
Im using QEventLoop to implement blocking mechanism (synchronous communication - ModBus protocol) without locking the main loop. I cannot use waitReadyRead() because I had problems with that function in the past (timeouts):
https://bugreports.qt-project.org/browse/QTBUG-24451
and
https://bugreports.qt-project.org/browse/QTBUG-14975
Someone can be curious why Im setting up so many threads:
Thread1: Each new communication creates a new thread and locks it with "global" mutex to ensure that no other function will execute parallel communication. Inside that thread - after preparations and locking mutex I communicate with QTcpSocket by Qt::QueuedConnection signal which is in Thread2 (constant communication with device).
Thread2: QTcpSocket object created and moved to thread. Once I connect with the device I dont want to close the socket. Because Im blocking main event loop I need other event loop to run signals from QTcpSocket.
And the code:
void someFunctionThatWantToSendData( void ) // Main Thread
{
ElfKernel::KernelSingleton::Instance().getGUIcontrol()->getCtrlUnitPtr()->execModbusCommand( someParameters, someCommunicationFunction );
}
ElfKernel::FrameReceived ControlUnit::execModbusCommand( std::list<unsigned int> paramsToCommand, FunctionStringList execCommand ) // Main Thread
{
ModbusCommandReply* mcr = new ModbusCommandReply(); // THREAD_1!!!!!! this object run in a Thread -> ModbusCommandReply : public QThread
auto timeout = ElfKernel::CommunicationManagerSingleton::Instance().getTimeout();
mcr->execute( paramsToCommand, execCommand ); // executes THREAD_1
bool hasFinishedWithoutTimeout = mcr->wait(timeout); // waiting for THREAD_1 to finish
FrameReceived ret = mcr->getData();
delete mcr;
return ret;
}
// this method is executed after preparations done by: mcr->execute( paramsToCommand, execCommand );
ElfKernel::FrameReceived CommunicationManager::getData( std::string data ) // THREAD_1
{
emit signalTcpSocketWriteData( data );
loop.exec(); // QEventLoop declared in a header; program loops until QTcpSocket::readyRead() signal will hit the slot TcpSocketClient::readyRead()
FrameReceived fr = tcpSocket->readDataString();
}
// executed by: emit signalTcpSocketWriteData( data );
void TcpSocketClient::writeDataSlot( std::string data ) // THREAD_2!!!!!
{
tcpSocket_->write( data );
tcpSocket_->flush();
}
void TcpSocketClient::readyRead( void ) // should be executed in THREAD_2 but signal readyRead() never arrives here because a get error on Output: "QSocketNotifier: socket notifiers cannot be disabled from another thread"
{
ElfKernel::CommunicationManagerSingleton::Instance().loop.quit(); // breaks loop.exec() in CommunicationManager::getData()
}
// constructor
CommunicationManager::CommunicationManager( void ) // Main Thread
{
tcpSocket = new TcpSocketClient();
tcpSocketThread = new QThread();
tcpSocket->moveToThread( tcpSocketThread );
QObject::connect( tcpSocketThread, SIGNAL(started()), tcpSocket, SLOT(prepare()) );
tcpSocketThread->start(); // CREATED THREAD_2!!!!!
QObject::connect(this, SIGNAL(signalTcpSocketWriteData(std::string)), tcpSocket, SLOT(writeDataSlot(std::string)), Qt::QueuedConnection );
QObject::connect(this, SIGNAL(signalTcpSocketReadData(std::string *)), tcpSocket, SLOT(readDataSlot(std::string *)), Qt::QueuedConnection);
// and other stuff
}
// constructor
TcpSocketClient::TcpSocketClient(QObject *parent) // Main Thread - before it is moved to THREAD_2
{
parent;
//prepare(); // it is executed after signal QThread::started() is emitted
}
// method run after thread started
void TcpSocketClient::prepare( void ) // THREAD_2
{
tcpSocket_ = new QTcpSocket(this);
QObject::connect(tcpSocket_, SIGNAL(disconnected()), this, SLOT(hostHaveDisconnected()));
QObject::connect(tcpSocket_, SIGNAL(readyRead()), this, SLOT(readyRead()));
}
So as I said slot TcpSocketClient::readyRead() will not be called and I get message on output: "QSocketNotifier: socket notifiers cannot be disabled from another thread".
If I replace this code:
ElfKernel::FrameReceived ControlUnit::execModbusCommand( std::list<unsigned int> paramsToCommand, FunctionStringList execCommand ) // Main Thread
{
ModbusCommandReply* mcr = new ModbusCommandReply(); // THREAD_1!!!!!! this object run in a Thread -> ModbusCommandReply : public QThread
auto timeout = ElfKernel::CommunicationManagerSingleton::Instance().getTimeout();
mcr->execute( paramsToCommand, execCommand ); // executes THREAD_1
bool hasFinishedWithoutTimeout = mcr->wait(timeout); // waiting for THREAD_1 to finish
FrameReceived ret = mcr->getData();
delete mcr;
return ret;
}
with:
ElfKernel::FrameReceived ControlUnit::execModbusCommand( std::list<unsigned int> paramsToCommand, FunctionStringList execCommand ) // Main Thread
{
FrameReceived ret = execCommand( paramsToCommand ); // Main Thread
return ret;
}
So the program is not pushed to thread but run in Main Thread (only difference!) then everything works fins - readyRead slot works loop breaks and I get the data. I need to run ModbusCommandReply as a thread because I set a mutex.lock() inside mcr->execute so whenever other part of my program run method execModbusCommand it will be stopped until other thread will free resources to establishe communication.
I dont understand why it says "QSocketNotifier: socket notifiers cannot be disabled from another thread" - i set up QTcpSocket inside THREAD_2 after the thread has started by putting new object on a heap: tcpSocket_ = new QTcpSocket(this);
I will be grateful for any help, thanks!
