Bitmap ArgumentException after returning in using statement

Question

So I am currently working on an image resizer which works/worked pretty fine but with the exception that it gave me an OutOfMemoryException when I was processing too many images at once crashing the program.

So in order to fix that I have wrapped the methods inside a using statement so the Bitmaps can be disposed correctly.

However I noticed that if I am returning my Bitmap inside the using statement I get this "ArgumentException was unhandled" message

Here my ImageResize method:

 public Bitmap ResizeImage(MemoryStream ms, Size size)
    {
        if (comboBox2.Text == "Pixel")
        {
            using (Bitmap img = new Bitmap(new Bitmap(ms, true), size.Width, size.Height))
            {
                var original = new Bitmap(ms, true);
                Graphics graphic = Graphics.FromImage(img);

                //IRRELEVANT CODE.....

                return img;
            }
        }
        else
        {
            return null;
        }

And here when i try to save my image outside the ImageResize method:

private void button1_Click(object sender, EventArgs e)
    {
    //IRRELEVANT CODE ...
    img = ResizeImage(memory, new Size(getX(), getY()));
    //IRRELEVANT CODE ...
    img.Save(outputFileName, codec, encoderParams); //<-Exception occurs here
    }

When I remove the using statement everything works perfectly fine again, however I have to use the using blocks to dispose the Bitmap and therefor to prevent the memory leak. Also when I save the image inside the using statement it works fine too, but that is not a solution in my case.

What am I doing wrong? To me it seems like the Bitmap is not returned correctly.

I appreciate any help and thanks in advance Ravand

Answer 1

Ok I finally fixed the problem with the memory leak, turned out that I was indeed releasing/disposing the images but it wasn't doing it quick enough which caused this outOufMemoryException when you were processing alot of very big images right after the other. I tried making everything multithreaded and always waiting for the WorkingSet to get smaller without success.

Turned out it was easier than I thhought, all I had to do is put this at the end of my resizing method:

GC.Collect();
GC.WaitForPendingFinalizers();
System.Threading.Thread.SpinWait(5000);

And this seems to do the magic for resizing big images with 10-20mb in size and with 10000x10000 for the resolution. Can somebody maybe explain why the SpinWait helps but not a normal thread sleep? Whenever I tried sleeping the thread it also seemed to sleep the releasing of the memory.

Answer 2

You put your using in the wrong place. After the end of the using block (which includes returning from it), the object controlled by the block is disposed. Accessing a disposed bitmap is an error.

Your using needs to be here instead:

private void button1_Click(object sender, EventArgs e)
{
    //IRRELEVANT CODE ...
    using(img = ResizeImage(memory, new Size(getX(), getY())))
    {
        //IRRELEVANT CODE ...
       img.Save(outputFileName, codec, encoderParams);
    }
}