Unexpected area to collect garbage in .NET



The .NET framework provides an intelligent garbage collector that saves us a trouble of manual memory management. And in 95% of cases you can forget about memory and related issues. But the remaining 5% have some specific aspects connected to unmanaged resources, too big objects, etc. And it’s better to know how the garbage is collected. Otherwise, you can get surprises.

Do you think GC is able to collect an object till its last method is complete? It appears it is. But it is necessary to run an application in release mode without debugging. In this case JIT compiler will perform optimizations that will make this situation possible. Of course, JIT compiler does it when the remaining method body doesn’t contain references to the object or its fields. It should seem a very harmless optimization. But it can lead to the problems if you work with the unmanaged resources: object compilation can be executed before the operation over the unmanaged resource is finished. And most likely it will result in the application crash.

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Unobviousness in use of C# closures



C# gives us an ability to use closures. This is a powerful tool that allows anonymous methods and lambda-functions to capture unbound variables in their lexical scope. And many programmers in .NET world like using closures very much, but only few of them understand how they really work. Let’s start with a simple sample:

public void Run()
{
  int e = 1;
  Foo(x => x + e);
}

Nothing complicated happens here: we just captured a local variable e in its lambda that is passed to some Foo method. Let’s see how the compiler will expand such construction.*

public void Run()
{
  DisplayClass c = new DisplayClass();
  c.e = 1;  
  Foo(c.Action);
}
private sealed class DisplayClass
{
  public int e;
  public int Action(int x)
  {
    return x + e;
  }
}

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Wrapping C# class for use in COM



Let us have a C# class that makes something useful, for example:

public class Calculator
{
    public int Sum(int a, int b)
    {
        return a + b;
    }
}

Let’s create a COM interface for this class to make it possible to use its functionality in other areas. At the end we will see how this class is used in Delphi environment.

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