Friday, May 1, 2009

Disposing COM objects

The Tridion solutions at my current assignment are working great, but now and then the CM website freezes. After investigating the issue with Tridion customer support, there is a suspicion the Tridion COM objects freeze under memory load.
This load is generated because our custom solutions do not release the COM objects they use. So now the codebase should be recoded with this cleanup operation.

When you don't cleanup this code, the cleanup will be initiated by the .NET Garbage Collector (GC). But the GC isn't working continually, but will only be called under memory pressure.
Because COM objects aren't run under as managed code, the GC doesn't know how much memory is used by them. Therefore, waiting until the GC will cleanup your code can take a long time, especially because COM objects are small objects on the managed memory.

The pattern to use for cleaning up unmanaged resources is the IDisposable interface. So with this pattern, we can release a COM object after you're done with it by calling the Marshal.ReleaseComObject method.

Because the Tridion Object Model (TOM) has a lot of objects, I'm creating a managed wrapper assembly, where on each object I can implement the IDisposable interface. Besides the interface, I need some more plumbing, so the first class to create is an abstract DisposableBase class:

public abstract class DisposableBase : IDisposable
{
private bool disposed = false;

protected void checkNotDisposed()
{
if (this.disposed)
{
string message = "Object of type " + base.GetType().Name + " cannot be accessed because it was disposed.";
throw new ObjectDisposedException(base.GetType().Name, message);
}
}

public void Dispose()
{
if (!this.disposed)
{
this.Dispose(true);
}
GC.SuppressFinalize(this);
}

protected virtual void Dispose(bool disposing)
{
if (!this.disposed)
{
this.DisposeMembers();
}
this.disposed = true;
}

protected abstract void DisposeMembers();

public static void ReleaseComObject(object interopObject)
{
if (interopObject != null)
{
Marshal.ReleaseComObject(interopObject);
}
interopObject = null;
}
}



So I can use this base class in each wrapper class for TOM classes, like the Component class:

public class Component : DisposableBase
{
private Tridion.ContentManager.Interop.TDS.Component comComponent;

public Component(Tridion.ContentManager.Interop.TDS.Component component)
{
comComponent = component;
}

~Component()
{
Dispose(false);
}

protected override void DisposeMembers()
{
DisposableBase.ReleaseComObject(comComponent);
}

public void CheckIn(bool permanentLock)
{
checkNotDisposed();
comComponent.CheckIn(permanentLock);
}

_Component Members
}


So now it's perfectly safe to use the TOM to check in a component with the following code:

using (Component component = tdse.GetObject("tcm:8-123", EnumOpenMode.OpenModeView))
{
component.CheckIn(true);
}

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