Using QQuickView in separate thread problems

[binaural]

Hi,

I'm trying to display qml file with help of QQuickView running in separate thread. My platform is beaglebone (am33xx qt5.5 compiled by yocto project with opengl).

I debug problem a bit and only after disabling of line 523 (in qtbase/src/gui/kernel/sources/qwindow.cpp)

d->platformWindow->setVisible(visible);

it was possible to use showFullScreen() in QquickView. The other show() function still doesn't work (means that the execution of the program is frozen after this place in code). The showFullScreen() is working restricted, it can show simple qml file, but doesn't show animation. There are some warnings in log file like :

WARNING: QObject::moveToThread: Current thread (0x6ff08) is not the object's thread (0x112740). Cannot move to target thread (0x156560)
WARNING: Updates can only be scheduled from GUI thread or from QquickItem::updatePaintNode()

When don't use separate thread and put everything in main.cpp then everything works as expected (including animations). Any ideas what could be wrong in my implementation? Thanks.

main.cpp:

#include <iostream>
#include <QGuiApplication>
#include <QQuickView>
#include "mythread.h"
#include <qdebug.h>
 
using namespace std;
 
int main(int argc, char ** argv)
{
	QGuiApplication app(argc, argv);
	qDebug() << "app.thread() " << QGuiApplication::instance()->thread();
 
	MyThread thread;
	thread.start();
 
	return app.exec();
}

#include <iostream>
#include <QGuiApplication>
#include <QQuickView>
#include "mythread.h"
#include <qdebug.h>

using namespace std;

int main(int argc, char ** argv)
{
	QGuiApplication app(argc, argv);
	qDebug() << "app.thread() " << QGuiApplication::instance()->thread();

	MyThread thread;
	thread.start();

	return app.exec();
}

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mythread.cpp:

#include "mythread.h"
#include <QDebug>
#include <QString>
#include <QMutexLocker>
#include <QTime>
 
 
MyThread::MyThread() {
	m_view = new QQuickView();
	engine = new QQmlApplicationEngine();
	window = NULL;
}
 
void MyThread::run() {
 
	qDebug() << "thread() " << currentThread();
 
	m_view->setSource(QUrl(QStringLiteral("qrc:/test/loadingView.qml")));
	m_view->show();
 
	exec();
}
 
void MyThread::setWindow(QQuickWindow* ptr) {
	if (ptr)
		window = ptr;
	else {
		window = new QQuickWindow();
	}
}

#include "mythread.h"
#include <QDebug>
#include <QString>
#include <QMutexLocker>
#include <QTime>


MyThread::MyThread() {
	m_view = new QQuickView();
	engine = new QQmlApplicationEngine();
	window = NULL;
}

void MyThread::run() {

	qDebug() << "thread() " << currentThread();

	m_view->setSource(QUrl(QStringLiteral("qrc:/test/loadingView.qml")));
	m_view->show();

	exec();
}

void MyThread::setWindow(QQuickWindow* ptr) {
	if (ptr)
		window = ptr;
	else {
		window = new QQuickWindow();
	}
}

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mythread.h

#ifndef MYTHREAD_H
#define MYTHREAD_H
 
#include <QThread>
#include <QMutex>
#include <QQuickView>
#include <QQmlApplicationEngine>
 
class MyThread : public QThread {
 
	Q_OBJECT
public:
	MyThread();
 
public slots:
	void run();
	void setWindow(QQuickWindow* ptr);
 
private:
 
	QQmlApplicationEngine *engine;
	QQuickWindow *window;
	QQuickView *m_view;
	QObject *topLevel;
 
};
 
#endif // MYTHREAD_H

#ifndef MYTHREAD_H
#define MYTHREAD_H

#include <QThread>
#include <QMutex>
#include <QQuickView>
#include <QQmlApplicationEngine>

class MyThread : public QThread {

	Q_OBJECT
public:
	MyThread();

public slots:
	void run();
	void setWindow(QQuickWindow* ptr);

private:

	QQmlApplicationEngine *engine;
	QQuickWindow *window;
	QQuickView *m_view;
	QObject *topLevel;

};

#endif // MYTHREAD_H

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qml file:

import QtQuick 2.0
import QtQuick.Window 2.2
 
Window {
	property var value: 0
	property string colGreyVeryLight:		"#cccccc"
	property string colGreyLight:			"#999999"
	property string colGrey:				"#444444"
	property string colGreyDark:			"#262a2b"
	property var timerIntervalTime: 250
 
	id: screen
	width: 800
	height: 480
	color: "black"
	objectName: "list"
 
	MouseArea {
		id: mouseArea
		width: 480
		height: 360
		anchors.rightMargin: 0
		anchors.bottomMargin: -497
		anchors.leftMargin: 8
		anchors.topMargin: 497
		anchors.fill: parent
	}
 
	Text {
		id: loadingText
		x: 300
		y: 67
		width: 180
		height: 30
		color: "#ffffff"
		text: qsTr("Loading...")
		font.bold: true
		verticalAlignment: Text.AlignVCenter
		horizontalAlignment: Text.AlignHCenter
		font.pointSize: 14
		font.pixelSize: 14
	}
 
	Timer {
		interval: timerIntervalTime; running: true; repeat: true
		onTriggered: (value == 4) ? value = 0 : value++
	}
 
	Rectangle {
		id: rect1
		x: 65
		y: 192
		width: 50
		height: 50
		color: (value == 0) ? colGreyVeryLight : ((value == 1) ? colGreyLight : (value == 2) ? colGrey : colGreyDark)
	}
 
	Rectangle {
		id: rect2
		x: 203
		y: 192
		width: 50
		height: 50
		color: (value == 1) ? colGreyVeryLight : ((value == 2) ? colGreyLight : (value == 3) ? colGrey : colGreyDark)
	}
 
	Rectangle {
		id: rect3
		x: 354
		y: 192
		width: 50
		height: 50
		color: (value == 2) ? colGreyVeryLight : ((value == 3) ? colGreyLight : (value == 4) ? colGrey : colGreyDark)
	}
 
	Rectangle {
		id: rect4
		x: 511
		y: 192
		width: 50
		height: 50
		color: (value == 3 ) ? colGreyVeryLight : ((value == 4) ? colGreyLight : colGreyDark)
	}
 
	Rectangle {
		id: rect5
		x: 674
		y: 192
		width: 50
		height: 50
		color: (value == 4 ) ? colGreyVeryLight : colGreyDark
	}
 
}

import QtQuick 2.0
import QtQuick.Window 2.2

Window {
	property var value: 0
	property string colGreyVeryLight:		"#cccccc"
	property string colGreyLight:			"#999999"
	property string colGrey:				"#444444"
	property string colGreyDark:			"#262a2b"
	property var timerIntervalTime: 250

	id: screen
	width: 800
	height: 480
	color: "black"
	objectName: "list"

	MouseArea {
		id: mouseArea
		width: 480
		height: 360
		anchors.rightMargin: 0
		anchors.bottomMargin: -497
		anchors.leftMargin: 8
		anchors.topMargin: 497
		anchors.fill: parent
	}

	Text {
		id: loadingText
		x: 300
		y: 67
		width: 180
		height: 30
		color: "#ffffff"
		text: qsTr("Loading...")
		font.bold: true
		verticalAlignment: Text.AlignVCenter
		horizontalAlignment: Text.AlignHCenter
		font.pointSize: 14
		font.pixelSize: 14
	}

	Timer {
		interval: timerIntervalTime; running: true; repeat: true
		onTriggered: (value == 4) ? value = 0 : value++
	}

	Rectangle {
		id: rect1
		x: 65
		y: 192
		width: 50
		height: 50
		color: (value == 0) ? colGreyVeryLight : ((value == 1) ? colGreyLight : (value == 2) ? colGrey : colGreyDark)
	}

	Rectangle {
		id: rect2
		x: 203
		y: 192
		width: 50
		height: 50
		color: (value == 1) ? colGreyVeryLight : ((value == 2) ? colGreyLight : (value == 3) ? colGrey : colGreyDark)
	}

	Rectangle {
		id: rect3
		x: 354
		y: 192
		width: 50
		height: 50
		color: (value == 2) ? colGreyVeryLight : ((value == 3) ? colGreyLight : (value == 4) ? colGrey : colGreyDark)
	}

	Rectangle {
		id: rect4
		x: 511
		y: 192
		width: 50
		height: 50
		color: (value == 3 ) ? colGreyVeryLight : ((value == 4) ? colGreyLight : colGreyDark)
	}

	Rectangle {
		id: rect5
		x: 674
		y: 192
		width: 50
		height: 50
		color: (value == 4 ) ? colGreyVeryLight : colGreyDark
	}

}

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[anda_skoa]

GUI, like QtQuick or QtWidgets, can only be used by the thread running the QApplication, i.e. usually that's the main thread.

That's ok in your code, as the QQuickView is generated by the main thread, but then you try to call the view's methods from the secondary thread.

If you want the secondary thread to trigger these functions, connect signals to these slots and emit them from the secondary thread.
The connect() mechanism will then take care of calling the slots in the thread of the receiver object, which here is the main thread and this safe.

Cheers,
_

[binaural]

Hi,

thanks for hint. I did update code accordingly and it start working:

MyThread::MyThread() {
	m_view = new QQuickView();
	connect(this, SIGNAL(show()), m_view, SLOT(show()));
	connect(this, SIGNAL(qmlSetSource(QUrl)), m_view, SLOT(setSource(QUrl)));
}
 
void MyThread::run() {
 
	qDebug() << "thread() " << currentThread();
	emit qmlSetSource(QUrl(QStringLiteral("qrc:/test/loadingView.qml")));
	emit show();
	exec();
 
}

MyThread::MyThread() {
	m_view = new QQuickView();
	connect(this, SIGNAL(show()), m_view, SLOT(show()));
	connect(this, SIGNAL(qmlSetSource(QUrl)), m_view, SLOT(setSource(QUrl)));
}

void MyThread::run() {

	qDebug() << "thread() " << currentThread();
	emit qmlSetSource(QUrl(QStringLiteral("qrc:/test/loadingView.qml")));
	emit show();
	exec();

}

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class MyThread : public QThread {
 
	Q_OBJECT
public:
	MyThread();
 
public slots:
	void run();
 
private:
 
	QQuickView *m_view;
 
signals:
	void show();
	void qmlSetSource(QUrl url);
 
};

class MyThread : public QThread {

	Q_OBJECT
public:
	MyThread();

public slots:
	void run();

private:

	QQuickView *m_view;

signals:
	void show();
	void qmlSetSource(QUrl url);

};

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One thing which remain is warning printed in console when run example:

13:26:30.192 WARNING: QObject::setParent: Cannot set parent, new parent is in a different thread
13:26:30.416 WARNING: Updates can only be scheduled from GUI thread or from QQuickItem::updatePaintNode()

Thanks

[anda_skoa]

Might be caused by some other code that you haven't posted yet.

The first one for example could be caused by creating an instance of a QObject derived class in run() and passing "this" as the parent.

Cheers,
_

[binaural]

Attaching full source (qml remains unchanged):

main.cpp

#include <iostream>
#include <QGuiApplication>
#include <QQuickView>
#include "mythread.h"
#include <qdebug.h>
 
using namespace std;
 
int main(int argc, char ** argv)
{
	QGuiApplication app(argc, argv);
	qDebug() << "app.thread() " << QGuiApplication::instance()->thread();
 
	MyThread thread;
	thread.start();
 
	return app.exec();
}

#include <iostream>
#include <QGuiApplication>
#include <QQuickView>
#include "mythread.h"
#include <qdebug.h>

using namespace std;

int main(int argc, char ** argv)
{
	QGuiApplication app(argc, argv);
	qDebug() << "app.thread() " << QGuiApplication::instance()->thread();

	MyThread thread;
	thread.start();

	return app.exec();
}

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mytheread.cpp

#include "mythread.h"
#include <QDebug>
#include <QString>
#include <QMutexLocker>
#include <QTime>
 
 
MyThread::MyThread() {
	m_view = new QQuickView();
	connect(this, SIGNAL(show()), m_view, SLOT(show()));
	connect(this, SIGNAL(qmlSetSource(QUrl)), m_view, SLOT(setSource(QUrl)));
}
 
void MyThread::run() {
 
	qDebug() << "thread() " << currentThread();
	emit qmlSetSource(QUrl(QStringLiteral("qrc:/test/loadingView.qml")));
	emit show();
	exec();
 
}

#include "mythread.h"
#include <QDebug>
#include <QString>
#include <QMutexLocker>
#include <QTime>


MyThread::MyThread() {
	m_view = new QQuickView();
	connect(this, SIGNAL(show()), m_view, SLOT(show()));
	connect(this, SIGNAL(qmlSetSource(QUrl)), m_view, SLOT(setSource(QUrl)));
}

void MyThread::run() {

	qDebug() << "thread() " << currentThread();
	emit qmlSetSource(QUrl(QStringLiteral("qrc:/test/loadingView.qml")));
	emit show();
	exec();

}

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mythread.h

#ifndef MYTHREAD_H
#define MYTHREAD_H
 
#include <QThread>
#include <QMutex>
#include <QQuickView>
#include <QQmlApplicationEngine>
 
class MyThread : public QThread {
 
	Q_OBJECT
public:
	MyThread();
 
public slots:
	void run();
 
private:
 
	QQuickView *m_view;
 
signals:
	void show();
	void qmlSetSource(QUrl url);
 
};
 
#endif // MYTHREAD_H

#ifndef MYTHREAD_H
#define MYTHREAD_H

#include <QThread>
#include <QMutex>
#include <QQuickView>
#include <QQmlApplicationEngine>

class MyThread : public QThread {

	Q_OBJECT
public:
	MyThread();

public slots:
	void run();

private:

	QQuickView *m_view;

signals:
	void show();
	void qmlSetSource(QUrl url);

};

#endif // MYTHREAD_H

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[anda_skoa]

Works for me.

I copied the QML content from the thread start and modified it to use a Rectangle as the top level element as QQuickView expects an Item.
I also change the URL to the local file.

Cheers,
_