Question

I have some IronPython code in a C# class that has the following two lines in a function:

void test(MyType request){
    compiledCode.DefaultScope.SetVarialbe("target", request);
    compiledCode.Execute();
}

I was writing some code to stress-test this/performance test it. The request object that I’m passing in is a List<MyType> with one million MyType‘s. So I iterate over this list:

foreach(MyType thing in myThings){
    test(thing);
}

And that works fine – runs in about 6 seconds. When I run

for(int x = 0; x < 1000; x++){
    foreach(MyType thing in myThings){
        test(thing);
    }
}

On the 19th iteration of the loop I get an OutOfMemoryException.

I tried doing Python.CreateEngine(AppDomain.CurrentDomain) instead, which didn’t seem to have any effect, and I tried

...
compiledCode.Execute();
compiledCode.DefaultScope.RemoveVariable("target");

Hoping that somehow IronPython was keeping the reference around. That roughly doubled the amount of time it took, but it still blew up at the same point.

Why is my code causing a memory leak, and how do I fix it?

Answer 1

So, it turns out I wasn’t thinking at all.

The target object object contains a StringBuilder that I’m adding lines to. About 10 lines per iteration, so apparently I can hold about 190 million lines of text in a StringBuilder before I run out of memory 😉