I have Qt GUI application that uses boost and std built with Qt 5.5 I have written some API code that listens for requests (that why I moved API part to separate QThread). For Linux and Mac everything works perfectly. But on windows an extra window appears behind the main GUI app when I start a thread.
this is my worker class
class Worker : public QObject
{
Q_OBJECT
public:
explicit Worker(int argc, char argv[], QObject parent = 0);
private:
int m_argc;
char* m_argv[7];
public slots:
bool stop();
void mainLoop();
};
and cpp
Worker::Worker(int argc, char argv[], QObject parent) :
QObject(parent)
{
m_argc = argc;
m_argv[0] = argv[0];
m_argv[1] = argv[1];
m_argv[2] = argv[2];
m_argv[3] = argv[3];
m_argv[4] = argv[4];
m_argv[5] = argv[5];
m_argv[6] = argv[6];
}
bool Worker::stop()
{
return currency::stop_rpc();
}
void Worker::mainLoop()
{
qDebug()<<"Starting worker mainLoop in Thread "<<thread()->currentThreadId();
currency::run_wallet_rpc(m_argc, m_argv);
}
And this is how I start my thread
m_worker = new Worker(argc, argv);
m_rpc_thread = new QThread();
m_worker->moveToThread(m_rpc_thread);
connect(m_rpc_thread, SIGNAL(started()), m_worker, SLOT(mainLoop()));
m_rpc_thread->start();
Any advice would be greatly appreciated! Have spent hours on this...
Related
I have QThreadPool which run some tasks.
I need also create new tasks in other tasks.
To do that i think implement something like following:
class Task : public QRunnable
{
QThreadPool *pool;
public:
Task (QThreadPool *p) : pool(p){}
void run()
{
static std::atomic<int> counter = ATOMIC_FLAG_INIT;
qDebug() << QThread::currentThreadId();
int c;
if ((c = counter.load(std::memory_order_acquire)) < 10) {
pool->start(new Task(pool));
counter.store(c + 1, std::memory_order_release);
}
}
};
int main(int argc, char *argv[])
{
//...
QThreadPool threadPool;
threadPool.start(new Task(&threadPool));
//...
}
But I'm not sure that this is the right approach.
I have an object MainWorker ran as a separate thread thanks to moveToThread method.
MainWorker has a member SubWorker which is also ran as a separate thread. Both threads are working in infinite loops.
The idea is, MainWorker and SubWorker both perform some separate computations. Whenever SubWorker is done computing, it should notify MainWorker with the result.
Therefore I intuitively made first connection between signal emitted by SubWorker and a slot of MainWorker, but it wasn't working, so I made two more connections to rule out some potential problems:
connect(subWorker, &SubWorker::stuffDid, this, &MainWorker::reportStuff)); //1
connect(subWorker, &SubWorker::stuffDid, subWorker, &SubWorker::reportStuff); //2
connect(this, &MainWorker::stuffDid, this, &MainWorker::reportStuffSelf); //3
It seems, that what is not working is exactly what I need - cross thread communication, because connection 2 and 3 works as expected. My question is: How do I make connection 1 work?
Edit: Apparently, after Karsten's explanation, it is clear that infinite loop blocks the EventLoop. So the new question is, how can I send messages (signals, whatever) from an infinite loop thread to its parent thread?
I am new to Qt, there is a high chance that I got it completely wrong. Here goes the minimal (not)working example:
MainWorker.h
class MainWorker : public QObject
{
Q_OBJECT
public:
MainWorker() : run(false) {}
void doStuff()
{
subWorker = new SubWorker;
subWorkerThread = new QThread;
subWorker->moveToThread(subWorkerThread);
connect(subWorkerThread, &QThread::started, subWorker, &SubWorker::doStuff);
if(!connect(subWorker, &SubWorker::stuffDid, this, &MainWorker::reportStuff)) qDebug() << "connect failed";
connect(subWorker, &SubWorker::stuffDid, subWorker, &SubWorker::reportStuff);
connect(this, &MainWorker::stuffDid, this, &MainWorker::reportStuffSelf);
subWorkerThread->start();
run = true;
while(run)
{
QThread::currentThread()->msleep(200);
emit stuffDid();
}
}
private:
bool run;
QThread* subWorkerThread;
SubWorker* subWorker;
signals:
void stuffDid();
public slots:
void reportStuff()
{
qDebug() << "MainWorker: SubWorker did stuff";
}
void reportStuffSelf()
{
qDebug() << "MainWorker: MainWorker did stuff (EventLoop is not blocked)";
}
};
SubWorker.h
class SubWorker : public QObject
{
Q_OBJECT
public:
SubWorker() : run(false) {}
void doStuff()
{
run = true;
while(run)
{
qDebug() << "SubWorker: Doing stuff...";
QThread::currentThread()->msleep(1000);
emit stuffDid();
}
}
private:
bool run;
public slots:
void reportStuff()
{
qDebug() << "SubWorker: SubWorker did stuff";
}
signals:
void stuffDid();
};
main.cpp
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
MainWorker *mainWorker = new MainWorker;
QThread *mainWorkerThread = new QThread;
mainWorker->moveToThread(mainWorkerThread);
QObject::connect(mainWorkerThread, &QThread::started, mainWorker, &MainWorker::doStuff);
mainWorkerThread->start();
return a.exec();
}
I want to make an application where the user will hit a QPushButton and this will trigger a secondary thread which will add some text to a QListWidget in the main window. But for a reason that I cannot figure out ,although the signal from the thread to the main window is emitted it never reaches the destination. Probably because the connection fails. But why this happens here is my code(my application is compiled using Visual Studio 2010):
mythread.h
#ifndef MY_THREAD_H
#define MY_THREAD_H
#include <QThread>
#include <QString>
class mythread:public QThread
{
Q_OBJECT
public:
void setName(QString& name);
signals:
void sendMsg(QString& msg);
protected:
void run();
private:
QString m_name;
QString msg;
};
#endif
mythread.cpp
#include "mythread.h"
void mythread::setName(QString& name)
{
m_name=name;
}
void mythread::run()
{
msg="Hello "+m_name;
emit sendMsg(msg);
}
mydialog.h:
#ifndef MY_DIALOG_H
#define MY_DIALOG_H
#include <QtGui>
#include "mythread.h"
class mydialog:public QDialog
{
Q_OBJECT
public:
mydialog();
public slots:
void receiveMsg(QString& msg);
void fillList();
private:
QListWidget list1;
QPushButton btn1;
QGridLayout layout;
mythread thread;
};
#endif
mydialog.cpp:
#include "mydialog.h"
mydialog::mydialog()
{
layout.addWidget(&list1,0,0);
btn1.setText("Find");
layout.addWidget(&btn1,0,1);
setLayout(&layout);
QString myname="leonardo";
thread.setName(myname);
connect(&btn1,SIGNAL(clicked()),this,SLOT(fillList()));
connect(&thread,SIGNAL(sendMsg(QString&)),this,SLOT(receiveMsg(Qstring&)));
}
void mydialog::fillList()
{
thread.start();
}
void mydialog::receiveMsg(QString& msg)
{
list1.addItem(msg);
}
find.cpp:
#include <QApplication>
#include "mydialog.h"
int main(int argc,char* argv[])
{
QApplication app(argc,argv);
mydialog window;
window.setWindowTitle("Find");
window.show();
return app.exec();
}
find.pro:
TEMPLATE = app
TARGET =
DEPENDPATH += .
INCLUDEPATH += .
# Input
HEADERS += mydialog.h mythread.h
SOURCES += find.cpp mydialog.cpp mythread.cpp
Two things:
In your second connect call, Qstring must be changed to QString
Qt cannot deliver QString& accross threads by default. There's two ways to fix this:
Change your Signals and Slots and the connect to use QString rather than QString&
Use qRegisterMetaType in order to make QString& usable.
I still recommend reading
https://www.qt.io/blog/2010/06/17/youre-doing-it-wrong
and Kari's comment
https://www.qt.io/blog/2010/06/17/youre-doing-it-wrong#commento-comment-name-a6fad43dec11ebe375cde77a9ee3c4331eb0c5f0bcac478ecbe032673e8ebc82
when working with threads, though.
First of all use const qualifier for arguments if you're not planning to modify it. After fixing typo in connection SLOT(receiveMsg(Qstring&)) and changing signals and slots signature to const references everything works fine
Yes, I know that you cannot use GUI things from non-GUI threads. However, it seems reasonable to be able to create a QWidget object, send it to the GUI thread, and then send signals to it. However, when I try to do so, I get errors that widgets cannot be moved. However, this seems to works:
#include <iostream>
#include <QApplication>
#include <QtConcurrentRun>
#include <QDialog>
class BasicViewer : public QDialog
{
Q_OBJECT
public:
void Function(const float a)
{
std::cout << a << std::endl;
}
};
struct BasicViewerWrapper : public QObject
{
Q_OBJECT
public:
BasicViewer WrappedBasicViewer;
void Function(const float a)
{
WrappedBasicViewer.Function(a);
}
};
#include "main.moc" // For CMake's automoc
void Function2()
{
BasicViewerWrapper basicViewerWrapper;
basicViewerWrapper.moveToThread(QCoreApplication::instance()->thread());
basicViewerWrapper.Function(2.0f);
}
void Function1()
{
Function2();
}
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QtConcurrent::run(Function1);
std::cout << "End" << std::endl;
return app.exec();
}
I have created a wrapper class with the same API as the QWidget that stores an instance of the QWidget I wanted to create directly. I AM allowed to create that wrapper, move it to the GUI thread, and then use it. My question is, is there a way to do this without having to write this wrapper? It seems quite tedious, and since the concept works, I don't understand why it cannot be done directly. Any thoughts?
----------- EDIT ---------------
The first example was a bad one, because it did not attempt to do anything with GUI elements. This example indeed generates "Cannot create children for a parent that is in a different thread."
#include <iostream>
#include <QApplication>
#include <QtConcurrentRun>
#include <QMessageBox>
class BasicViewer : public QMessageBox
{
Q_OBJECT
public:
};
struct BasicViewerWrapper : public QObject
{
Q_OBJECT
public:
BasicViewer WrappedBasicViewer;
void exec()
{
WrappedBasicViewer.exec();
}
};
#include "main.moc" // For CMake's automoc
void Function2()
{
BasicViewerWrapper basicViewerWrapper;
basicViewerWrapper.moveToThread(QCoreApplication::instance()->thread());
basicViewerWrapper.exec();
}
void Function1()
{
Function2();
}
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QtConcurrent::run(Function1);
return app.exec();
}
----------- EDIT 2 ----------------
I thought this would work, since the member object gets created after the thread of the Wrapper has been moved:
#include <iostream>
#include <QApplication>
#include <QtConcurrentRun>
#include <QMessageBox>
class BasicViewer : public QMessageBox
{
Q_OBJECT
public:
};
struct BasicViewerWrapper : public QObject
{
Q_OBJECT
public:
BasicViewer* WrappedBasicViewer;
void exec()
{
WrappedBasicViewer->exec();
}
void create()
{
WrappedBasicViewer = new BasicViewer;
}
};
#include "main.moc" // For CMake's automoc
void Function2()
{
BasicViewerWrapper basicViewerWrapper;
basicViewerWrapper.moveToThread(QCoreApplication::instance()->thread());
basicViewerWrapper.create();
basicViewerWrapper.exec();
}
void Function1()
{
Function2();
}
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QtConcurrent::run(Function1);
return app.exec();
}
Unfortunately, it does not. Can anyone explain why?
--------------- EDIT 3 --------------------
I'm unsure why this works? It uses a signal to trigger the GUI component, but isn't the GUI object (the QDialog) still created in the non-GUI thread?
#include <iostream>
#include <QApplication>
#include <QtConcurrentRun>
#include <QMessageBox>
class DialogHandler : public QObject
{
Q_OBJECT
signals:
void MySignal(int* returnValue);
public:
DialogHandler()
{
connect( this, SIGNAL( MySignal(int*) ), this, SLOT(MySlot(int*)), Qt::BlockingQueuedConnection );
}
void EmitSignal(int* returnValue)
{
emit MySignal(returnValue);
}
public slots:
void MySlot(int* returnValue)
{
std::cout << "input: " << *returnValue << std::endl;
QMessageBox* dialog = new QMessageBox;
dialog->addButton(QMessageBox::Yes);
dialog->addButton(QMessageBox::No);
dialog->setText("Test Text");
dialog->exec();
int result = dialog->result();
if(result == QMessageBox::Yes)
{
*returnValue = 1;
}
else
{
*returnValue = 0;
}
delete dialog;
}
};
#include "main.moc" // For CMake's automoc
void MyFunction()
{
DialogHandler* dialogHandler = new DialogHandler;
dialogHandler->moveToThread(QCoreApplication::instance()->thread());
int returnValue = -1;
dialogHandler->EmitSignal(&returnValue);
std::cout << "returnValue: " << returnValue << std::endl;
}
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QtConcurrent::run(MyFunction);
std::cout << "End" << std::endl;
return app.exec();
}
Qt insists that widgets be created within the GUI thread. It disables moving widgets to different threads to prevent them from existing outside of the GUI thread. Your example above does not, in fact, move the BasicViewer to a different thread; it only moves BasicViewerWrapper to a different thread. You can see this if you print out the pointer to the containing thread within BasicViewerWrapper::Function and BasicViewer::Function:
std::cout << std::hex << thread() << std::endl;
If you really wish to trigger the creation of widgets from outside the GUI thread, it is more advisable for other threads to notify the GUI thread to create the widgets that you desire. You can either emit a signal from the non-GUI thread that connects to a slot in the GUI thread that creates the widgets, or you can invoke a function within the GUI thread to create the widgets for you using QMetaObject::invokeMethod.
EDIT
Unfortunately, there is no way to invoke a method in a different thread other than QMetaObject::invokeMethod if you are attempting to perform the invocation outside of a QObject. In the past, I've tried to tackle readability by placing the method invocation in a separate class or function, but admittedly, it's not perfect.
Your 3rd example is not working because QObject::moveToThread is not synchronous. Control must return to the destination thread's event loop before the object is actually moved to the destination thread. As such, you probably need a combination of a sleep statement and a call to QCoreApplication::processEvents after calling moveToThread. After these calls, you should probably call basicViewerWrapper::create() and basicViewerWrapper::exec() via QMetaObject::invokeMethod.
All right here we go:
This is all over the internet, but it does not seems to be working for me, the thing is I have two threads, Worker and p4, p4 sends a time to wait and other params to the worker, and I want that to be processed in a different thread, but then update the main thread with the results.
so, Worker.h looks like this:
#include <QObject>
class Worker : public QObject
{
Q_OBJECT
public:
int time;
int actual_weight;
int supported_weigth;
Worker();
~Worker();
public slots:
void process();
signals:
void finished();
};
Worker.cpp looks like this:
#include "worker.h"
#include <QDebug>
#include <iostream>
using namespace std;
Worker::Worker()
{
}
Worker::~Worker(){
}
void Worker::process(){
cout << "sleep!" << endl;
sleep(this->time);
cout << "done!" << endl;
//more_nonsense_stuff();
emit finished();
}
and then in my main thread I have this:
QThread* t = new QThread;
Worker* w = new Worker();
w->time = this->transactions[i].time;
connect(t, SIGNAL(started()), w, SLOT(process()));
connect(w, SIGNAL(finished()), this, SLOT(update_gui()));
w->moveToThread(t);
t->start();
the thing is that the SLOT update_gui() is defined in the main window header and implemented in the .cpp, but it never gets to execute.
I have tried attaching Qt::DirectConnection, and the gui updates, but when worker is finished... the whole program closes.
I've looked this but didn't worked for me (or I didn't understand), also looked at this but that says what I'm trying to do is unsafe??
please help, what am I doing wrong?