CODEWITHSUNDEEP
c#wpfmemory-managementmemory-leaksrendertargetbitmap
Olivia Trewin
Olivia Trewin

Reputation: 217

Memory leak in RenderTargetBitmap

I'm using a RenderTargetBitmap to render a set of controls in order to generate a PDF. The following code segment is the relevant section:

public Drawing.Image RenderPageBitmap()
{
    RenderTargetBitmap bit = null;
    Drawing.Bitmap bmp = null;
    try
    {
        bit = new RenderTargetBitmap(ImageSource.PixelWidth, ImageSource.PixelHeight, 96, 96, PixelFormats.Pbgra32);

        var viewBox = GetPageXaml(); //This method loads some prebuilt XAML from an embedded resource, setting the DataContext as needed.
        var siz = new Size(bit.PixelWidth, bit.PixelHeight);
        viewBox.Measure(siz);
        viewBox.Arrange(new Rect(siz));
        viewBox.UpdateLayout();

        var draw = new DrawingVisual();
        using (var graph = draw.RenderOpen())
            graph.DrawRectangle(new BitmapCacheBrush(viewBox), null, new Rect(siz));

        bit.Render(draw);
        bit.Freeze();

        bmp = new Drawing.Bitmap(bit.PixelWidth, bit.PixelHeight, Imaging.PixelFormat.Format32bppPArgb);

        var data = bmp.LockBits(new Drawing.Rectangle(Drawing.Point.Empty, bmp.Size), ImageLockMode.WriteOnly, Imaging.PixelFormat.Format32bppPArgb);
        {
            bit.CopyPixels(Int32Rect.Empty, data.Scan0, data.Height * data.Stride, data.Stride);
        }
        bmp.UnlockBits(data);

        return bmp;
    }
    catch (Exception)
    {
        bmp?.Dispose();
        throw;
    }
    finally
    {
        bit?.Clear();

        GC.Collect();
        GC.WaitForPendingFinalizers();
        GC.Collect();
    }
}

Even following other answers on StackOverflow and other forums (like clearing the bitmap and performing a garbage collection) doesn't seem to solve the issue. Each loop of this code can leak ~100MB of memory, which means I quickly hit the ~2GB limit of 32-bit processes.

The leak seems to occur on the RenderTargetBitmap.Render method exclusively, even the DrawingContext.DrawRectangle call doesn't noticeably increase memory usage.

Is there anything I can do to solve this problem?

Here's a snapshot of the memory usage as viewed through JetBrains' dotMemory. Clearly, the .Net heap is correctly cleared, but the unmanaged memory continues to grow.

Memory snapshot

Upvotes: 0

Views: 2140

Answers (3)

geraphl
geraphl

Reputation: 315

There seems to be a problem in WPF where the image source is kept in memory even after garbage collection has run.

I found this entry and it worked for me https://github.com/dotnet/wpf/issues/2397

So the solution is to call

viewBox.Content.Source = null;
viewBox.Content.UpdateLayout();

(I don't know where the image content might be in your code) after

bit.Freeze();

Upvotes: 0

user9429616
user9429616

Reputation: 9

Remove bit.Freeze();. Garbage collection does not collect frozen objects.

Upvotes: 0

CharithJ
CharithJ

Reputation: 47510

You return the Bitmap to somewhere. Make sure you Dispose the Bitmap instance once you are done with it. What you are doing in the finally is useless when there is memory leak. If there are references GC wouldn't collect it.

Each loop of this code can leak ~100MB of memory, which means I quickly hit the ~2GB limit of 32-bit processes.

Are you assuming there is a memory leak? May be there is no memory leak. I would get a good memory profiling tool and test this.

I have used ANTS Memory profiler and I find it good (it comes with 14 days trial). Just execute your logic a few times and see the Instance List if anything is growing. If so, look at the Retention graph to see what holds onto it. That will tell you what exactly happening. Root causes for memory leaks are quite difficult to guess sometimes, fortunately there are good tools for that.

Upvotes: 0

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