Copy objects -> copy gets slower

MHermann

Hi all,
I have following situation:

QtObject {
    id: blub
    property var obj: ({}) 
}

This property is changed regularly.
The new value is received by a signal and then copied.
But it gets slower with each copy.
For example, the first copy takes 180ms, after a few times it takes 600ms.

I tried different ways to copy it:

1) blub.obj = newValue
2) blub.obj = JSON.parse(JSON.stringify(newValue))
3) blub.obj = Object.assign({}, newValue);

What am I doing wrong?
How can I prevent it from slowing down with every copy?

SGaist

Hi,

Which version of Qt ?
On which OS ?
What is newValue ?

Can you provide a minimal compilable example that shows this issue ?

MHermann

Hi,

I am using Qt5.12.7.
I am developing the app on Linux and then it gets cross-compiled to run Raspbian.
newValue is a big json-object.

At the moment I don't have a minimal example.

Has anyone ever had the problem that copying values becomes slower over time?

JonB

@MHermann
Others will know more than I. Just some thoughts.

Just how big is "big"? MBs? GBs?
I can imagine/guess that after the initial setting of the property it will destroy its current value before replacing it with a new one. That could add (quite?) some time to copies after the first time?
Is this specifically a JSON issue? If you create a property which is, say, a huge string do you see the same slow down over time?
Are you able to test with the last Qt 5.15 instead of your 5.12?

MHermann

Thanks for your answer.
In meanwhile I was able to solve this problem.
I think it was related to the singleton.
The QtObject blub was in a singleton-qml-module.
Now I moved this QtObject to the main-qml-module.
Now the copy is much faster and it does not get slower.