Memory not released when multiple Image is loaded continuously

[Axel Spoerl]

That doesn’t clear the cache.
If no caching is needed/wanted, set the cache property to false.

[AdarshKale]

@Axel-Spoerl Hello,
I have already tried setting the cache to false. still, I could see that the memory kept increasing.
Is there any way to stop caching the pixmaps?

[Axel Spoerl]

Let’s ask the question the other way round: why is it a problem? What’s bad about caching pixmaps and images? And why don’t you just read the related documentation?

[gfxx]

why not use opencv for load image and only after qimage or qml code .... on opencv you can "free" or "clear" at every cicle ..... any how you are sure after usage you clear qimage? maybe, if a loop, there are something of wrong. After load qimage you can show and in row after clear ..... so no buffer ..... better is you declare the same qimage name at every cicle ..... as void var and not a global one for example.

[AdarshKale]

@Axel-Spoerl
To provide you with the background of the problem: This is for an infotainment project
I am developing the animation for a Wheel rotation, based on the wheel angle,

As and when the wheel angle changes, I need to show the axle movement in terms of animation from the old angle to the new angle,
To achieve this, for a smoother animation, we have decided to show a sequence of images with a Timer (We have around 50 images from extreme left to extreme right).

When the angle changes from 10 degrees to 20 degrees, we show the sequence of images every 100ms from 10 to 20 (some 10 images).

Here Image component is used in QML.

property int wheelValue:0

Image
        {
            id:itm_wheel
            source: "Wheel_0"+wheelValue+".png"
            cache: false // even tried enabling the cache.
        }

// wheelValue is updated via Timer 
 Timer
    {
        id: wheelTimer
        repeat: true
        running: false
        interval: 100
        onTriggered:
        {
                // Some logic to monitor the wheel angle and update the wheelValue
                wheelValue+=1
                wheelTimer.restart() // until the actual wheel angle is met.
               
                // Stop the timer when the actual wheel value is met.
                  wheelTimer.stop()
           }
    }

We have only 512 MB of memory available,
Each asset .png used for this animation is some 10kb.

When we keep the animation for some 30 minutes with random updates in wheel angle, we see the accumulation of memory which is never getting freed.

Hence we need some way to implement this without accumulating memory.
Thanks

[Axel Spoerl]

Let's maybe take one step back.

a) Memory leak
There is no memory leak.

b) Use case
Are we really sure, that all pixmaps / images are really used only once?
Which operating system is used? How about e.g. the XCB backing store? What happens, if a displayed image is covered / uncovered by other screen assets? Do you really wanna re-render in that case?
Why is caching a problem at all?
Do we not have enough memory?

Edit:
Sorry, our messages have crossed.
If you want to show a total of 50 different images and have smooth movements, 512MB of RAM is probably too little.
I'd try it out on a host with sufficient RAM and see what's the minimum required memory.
Maybe reducing the images in size and number helps.

[AdarshKale]

@Axel-Spoerl said in Memory not released when multiple Image is loaded continuously:

b) Use case
Are we really sure, that all pixmaps / images are really used only once?

we may come across the same image again during the same angle received.

Which operating system is used?

QNX

How about e.g. the XCB backing store? What happens, if a displayed image is covered / uncovered by other screen assets? Do you really wanna re-render in that case?

We are handing the visibleChanged property from QML to stop the animation if it is not on that screen.
Directly we render the exact Image for the current position then when this screen is rendered.

Why is caching a problem at all?
Do we not have enough memory?

We don't have enough memory.

Edit:
If you want to show a total of 50 different images and have smooth movements, 512MB of RAM is probably too little.
Maybe reducing the images in size and number helps.

Reducing the images would not solve the issue, but it postpones it.

[AdarshKale]

Need a clean way to not accumulate the memory on every reload of the QML Image

[Axel Spoerl]

One step back again: What's the problem? The cache should resize, if the application runs out of memory. Does your application crash?

[AdarshKale]

@Axel-Spoerl said in Memory not released when multiple Image is loaded continuously:
**The cache should resize

I don't see the cache getting resized.
if I run the top command and perform a script to continuously run the angle change,
I get the memory utilized increased - leading to low memory, once the memory reaches below 15MB or so, the System Hangs, and after few seconds application crashes.

Even if we come out of that screen during the update, the memory utilisation stops and is never freed.

[Axel Spoerl]

Which Qt version are you using?

[AdarshKale]

@Axel-Spoerl said in Memory not released when multiple Image is loaded continuously:

Which Qt version are you using?

5.15

[Axel Spoerl]

That explains a lot. Outdated version. There is a memory leak in the quick pixmap cache, and it won't be fixed.
Upgrade to Qt 6.7.

[AdarshKale]

However, we cannot upgrade to newer Qt versions at this stage of the project.
Is there any other way possible?

There should be some workaround to clear the accumulated memory.?

[Axel Spoerl]

Qt 5.15 is an outdated Qt version. Given the simplicity of the project, cannot sound more like don't want to.
There is no other way possible and a workaround for 5.15 will not be implemented.

[AdarshKale]

There are a few deprecated APIs used and many syntax changes if we upgrade to the latest 6.x version which is risky at this stage.
hence we are finding an alternative way.

Any possibility of calling garbage collection periodically?
Will this accumulated memory get freed with garbage collection?

[JonB]

@AdarshKale said in Memory not released when multiple Image is loaded continuously:

Any possibility of calling garbage collection periodically?
Will this accumulated memory get freed with garbage collection?

No. No.

If you read referenced QTBUG you would see how involved the code is, and that it has been integrated into Qt6.x.

[Axel Spoerl]

@AdarshKale

There are a few deprecated APIs used and many syntax changes if we upgrade to the latest 6.x version which is risky at this stage.

How complex and risky can an opensource wheel rotation app be, when it has to fit into 500MB of RAM including OS and Qt?

hence we are finding an alternative way.

No matter how often you ask: Upgrade to Qt6 is the only option.

[GrecKo]

@Axel-Spoerl said in Memory not released when multiple Image is loaded continuously:

Qt 5.15 is an outdated Qt version. Given the simplicity of the project, cannot sound more like don't want to.

You've got to chill. Qt 5.15 is still a supported LTS version. Doing a major version upgrade of a big depency like Qt is not a small meaningless task. It's very understandable that this can't been done in an advanced stage of a project.

@AdarshKale as it seems there is no easy fix for your issue in Qt 5, a workaround would be to not use Image. What do you mean by wheel rotation? Is that changing the angle or rotating between multiple images? The formzr could be done by animating the rotation property.
Alternatively if you do need to have multiple images, you could try implementing a custom QQuickPaintedItem and painting your images there, bypassing the QtQuick cache.

[jeremy_k]

Has precreating all of the required Image instances been tried?

I haven't delved into the pixmap cache bug, but the description suggests that it is loading (and unloading) that causes the leak, rather than repeat references to loaded data. Rather than changing the source of a single Image, just set the current image.visible to false, and the next to true.

Another alternative is to attempt to structure the animation as a transformation of a single Image.