How is the context of WorkerScript defined?

[tube42]

I am trying to move some computation-intensive code to a worker thread, as recommended by Nokia documents. The basic outline of the code is something like this:

// Test.qml
import QtQuick 1.0
import com.meego 1.0

Page {
	id: page
	// ...

	WorkerScript {
		id: worker
		source: "Worker.js"
		onMessage: ...
	}

	DataModel {id : dataModel }

	function startWorker() {
		var msg = { page : page, test : 123, dataModel : dataModel };
		worker.sendMessage(msg);
        }
    }
}
//

With the javascript part like this

// in Worker.js
WorkerScript.onMessage = function(message) {	
	var obj = Qt.createQmlObject("QML code here", message.page, "myObject42");
	WorkerScript.sendMessage({ result: obj});
}
//

I have two problems with this code: first of all, the message from QML to JS is altered for some reason I dont understand. This is what I have in the calling QML:
DEBUG: page Test_QMLTYPE_44(0x1fbc4f68)
DEBUG: test 123
DEBUG: dataModel QDeclarativeListModel(0x1fbb8ac8)

And this is what the receiving JS code sees:
DEBUG: page null
DEBUG: test 123
DEBUG: dataModel QDeclarativeListModelWorkerAgent(name = "")

Notice that page is now NULL.


Second, the Qt component is not available in the JS code, resulting in this error:
TypeError: Result of expression 'Qt.createQmlObject' [undefined] is not a function
(no, this is not due to "page" being null, the result is the same of I use dataModel as parent)


Can anyone please tell me why this is happening?

[tube42]

I should probably add that I can get the app to coredump on N950 by adding Qt.createQmlObject to the message. That is:

var msg = { page : page, test : 123, dataModel : dataModel, oh_crap:  Qt.createQmlObject };
worker.sendMessage(msg);

[gnuton]

Hi here the answers to your questions:
1. page is not object you can pass to the worker script; the integer is copied and the dataModel variable is actually referring to your model trough a "proxy" object (QDeclarativeListModel).
So definitely it works as expected.
2. You cannot create any QObject in worker script.

[tube42]

Thank you gnuton,

I actually suspected this, but could not find any documentation confirming that. I hope the QML team understands that these limitations make WorkerScript useless for certain not-so-uncommon tasks.

[gnuton]

Hi tube,
I believe those are a kind of technical limitations. BTW in case you cannot really achieve something in a different way using a worker script you can still subclass QAbstractListModel and perform operations in different a thread using C++.
From my experience I suggest you to avoid using QAbstractTableModel with QML views since those display only the first row of your table.