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问题:

I have some C# code in an ASP.Net application that does this:

Bitmap bmp = new Bitmap(1184, 1900);

And occasionally it throws an exception "Parameter is not valid". Now i've been googling around and apparently GDI+ is infamous for throwing random exceptions, and lots of people have had this problem, but nobody has a solution to it! I've checked the system and it has plenty of both RAM and swap space. Now in the past if i do an 'iisreset' then the problem goes away, but it comes back in a few days. But i'm not convinced i've caused a memory leak, because as i say above there is plenty of ram+swap free.

Anyone have any solutions?

回答1:

Stop using GDI+ and start using the WPF Imaging classes (.NET 3.0). These are a major cleanup of the GDI+ classes and tuned for performance. Additionally, it sets up a "bitmap chain" that allows you to easily perform multiple actions on the bitmap in an efficient manner.

Find more by reading about BitmapSource

Here's an example of starting with a blank bitmap just waiting to receive some pixels:

using System.Windows.Media.Imaging;
class Program {
    public static void Main(string[] args) {
        var bmp = new WriteableBitmap(1184, 1900, 96.0, 96.0, PixelFormat.Bgr32, null);
    }
}

回答2:

For anyone who's interested, the solution i'm going to use is the Mono.Cairo libraries from the mono C# distribution instead of using system.drawing. If i simply drag the mono.cairo.dll, libcairo-2.dll, libpng13.dll and zlib1.dll files from the windows version of mono into the same folder as my executable, then i can develop in windows using visual studio 2005 and it all works nicely.

Update - i've done the above, and stress tested the application and it all seems to run smoothly now, and uses up to 200mb less ram to boot. Very happy.

回答3:

Everything I've seen to date in my context is related to memory leaks / handle leaks. I recommend you get a fresh pair of eyes to investigate your code.

What actually happens is that the image is disposed at a random point in the future, even if you've created it on the previous line of code. This may be because of a memory/handle leak (cleaning some out of my code appears to improve but not completely resolve this problem).

Because this error happens after the application has been in use for a while, sometimes using lots of memory, sometimes not, I feel the garbage collector doesn't obey the rules because of some special tweaks related to services and that is why Microsoft washes their hands of this problem.

http://blog.lavablast.com/post/2007/11/The-Mysterious-Parameter-Is-Not-Valid-Exception.aspx

回答4:

You not only need enough memory, it needs to be contiguous. Over time memory becomes fragmented and it becomes harder to find big blocks. There aren't a lot of good solutions to this, aside from building up images from smaller bitmaps.

new Bitmap(x, y) pretty much just needs to allocate memory -- assuming that your program isn't corrupted in some way (is there any unsafe code that could corrupt the heap), then I would start with this allocation failing. Needing a contiguous block is how a seemingly small allocation could fail. Fragmentation of the heap is something that is usually solved with a custom allocator -- I don't think this is a good idea in IIS (or possible).

To see what error you get on out of memory, try just allocation a gigantic Bitmap as a test -- see what error it throws.

One strategy I've seen is to pre-allocate some large blocks of memory (in your case Bitmaps) and treat them as a pool (get and return them to the pool). If you only need them for a short period of time, you might be able to get away with just keeping a few in memory and sharing them.

回答5:

I just got a reply from microsoft support. Apparently if you look here:

http://msdn.microsoft.com/en-us/library/system.drawing.aspx

You can see it says "Classes within the System.Drawing namespace are not supported for use within a Windows or ASP.NET service. Attempting to use these classes from within one of these application types may produce unexpected problems, such as diminished service performance and run-time exceptions." So they're basically washing their hands of the issue. It appears that they're admitting that this section of the .Net framework is unreliable. I'm a bit disappointed.

Next up - can anyone recommend a similar library to open a gif file, superimpose some text, and save it again?