QtWebkit multithreading

[ananya]

I am working on a project to render text as images using QT-Jambi.

The webkit renders the HTML and generates the image.
While running the code with a single thread there are no issue
but when I run the program using multiple threads(5-6) with each thread making multiple calls the getImage() the code crashes

for each thread I am passing a new QWebPage and using QWebPgae.moveToThread().

@    public void getImage(String str, int width, String fname,
   boolean istransparent) {

  
  QSize qSize = new QSize(width,height);


  page.setViewportSize(qSize);
  str = applyStyle(str);

  page.mainFrame().setHtml(str);
  String imageName = fname + "_" + width + "x"
    + page.mainFrame().contentsSize().height() + ".png";

  System.out.println("Creating Full Image : " + imageName);
  page.setViewportSize(page.mainFrame().contentsSize());

  
  QImage qImage = new QImage(page.mainFrame().contentsSize(),
    QImage.Format.Format_ARGB32);
  

  QPainter painter = new QPainter(qImage);

  page.mainFrame().render(painter);
  if (istransparent)
   makeTransparent(qImage);

  qImage.save(imageName);
  painter.end();

  
  qImage.dispose();
    
 }


@

@

An unexpected error has been detected by Java Runtime Environment:

SIGSEGV (0xb) at pc=0x03534417, pid=6123, tid=1902168976

Java VM: OpenJDK Server VM (1.6.0-b09 mixed mode linux-x86)

Problematic frame:

C [libQtWebKit.so.4+0x567417]

If you would like to submit a bug report, please visit:

http://icedtea.classpath.org/bugzilla

The crash happened outside the Java Virtual Machine in native code.

See problematic frame for where to report the bug.

@

@"COMPLETE CORE DUMP AT":http://freetexthost.com/1dtmb03qup
@

[andre]

Please don't double-post. I have deleted the duplicate of this posting that you put in General and Desktop.

[dangelog]

QtWebkit classes are GUI classes and as such they are meant to be used from the main thread only.

[ananya]

I am passing a new instance of QWebPage to each thread
MyClass contains imageGenerator()

@.....in main()...
QWepPage page = new QWebPage();
MyClass m = new MyClass();
QThread thread = new QThread(m)

page.moveToThread(thread);

thread.start();
.....
@

[goetz]

[quote author="ananya" date="1314020743"]I am passing a new instance of QWebPage to each thread
[/quote]

I just can emphasize what peppe wrote:

[quote author="peppe" date="1314019276"]QtWebkit classes are GUI classes and as such they are meant to be used from the main thread only.[/quote]

So, you must not move the web page to another thread.

[ananya]

Is there any work around for this then? while still keeping it multi threaded?

p.s.
i've found that the part of code that is causing the crash is
@page.mainFrame().setHtml(str);@

[goetz]

[quote author="ananya" date="1314022398"]Is there any work around for this then? while still keeping it multi threaded?[/quote]

Sure, if you don't mind what you are trying to achieve, we can give advice.

[ananya]

I am trying to make an application to convert text to image ...one requirement is that i should be able to run multiple threads since i plan to integrate this with a web server

[dangelog]

It's not possible with Qt. Can't you just run multiple processes?

[goetz]

All you can do is running multiple threads that collect the data (HTML pages) and send that to the QWebPage instances in the main thread.

[ananya]

[quote author="Volker" date="1314056869"]All you can do is running multiple threads that collect the data (HTML pages) and send that to the QWebPage instances in the main thread.[/quote]

that wont really serve my purpose of generating images in parallel

[quote author="peppe" date="1314023870"]It's not possible with Qt. Can't you just run multiple processes?[/quote]

will try to run it as a process..and get back

[ananya]

[quote author="ananya" date="1314062413"]
[quote author="Volker" date="1314056869"]All you can do is running multiple threads that collect the data (HTML pages) and send that to the QWebPage instances in the main thread.[/quote]

that wont really serve my purpose of generating images in parallel

[quote author="peppe" date="1314023870"]It's not possible with Qt. Can't you just run multiple processes?[/quote]

will try to run it as a process..and get back
[/quote]

Suppose i use Callable instead of Runnable threads
Is it possible to initialize a new QApplication within each callable's call...when i'm trying this only the first callable runs..the others crash

[lgeyer]

You can only have one Q(Core)Application instance. You might delete the instance and create a new but ... there can be only one!

[anjna]

"You can only have one Q(Core)Application instance. You might delete the instance and create a new but … there can be only one!"

How to do this? please help