Start with these simple classes...
Let's say I have a simple set of classes like this:
class Bus
{
Driver busDriver = new Driver();
}
class Driver
{
Shoe[] shoes = { new Shoe(), new Shoe() };
}
class Shoe
{
Shoelace lace = new Shoelace();
}
class Shoelace
{
bool tied = false;
}
A Bus has a Driver, the Driver has two Shoes, each Shoe has a Shoelace. All very silly.
Add an IDisposable object to Shoelace
Later I decide that some operation on the Shoelace could be multi-threaded, so I add an EventWaitHandle for the threads to communicate with. So Shoelace now looks like this:
class Shoelace
{
private AutoResetEvent waitHandle = new AutoResetEvent(false);
bool tied = false;
// ... other stuff ..
}
Implement IDisposable on Shoelace
Buit now FxCop will complain: "Implement IDisposable on 'Shoelace' because it creates members of the following IDisposable types: 'EventWaitHandle'."
Okay, I implement IDisposable on Shoelace and my neat little class becomes this horrible mess:
class Shoelace : IDisposable
{
private AutoResetEvent waitHandle = new AutoResetEvent(false);
bool tied = false;
private bool disposed = false;
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
~Shoelace()
{
Dispose(false);
}
protected virtual void Dispose(bool disposing)
{
if (!this.disposed)
{
if (disposing)
{
if (waitHandle != null)
{
waitHandle.Close();
waitHandle = null;
}
}
// No unmanaged resources to release otherwise they'd go here.
}
disposed = true;
}
}
Or (as pointed out by commenters) since Shoelace itself has no unmanaged resources, I might use the simpler dispose implementation without needing the Dispose(bool) and Destructor:
class Shoelace : IDisposable
{
private AutoResetEvent waitHandle = new AutoResetEvent(false);
bool tied = false;
public void Dispose()
{
if (waitHandle != null)
{
waitHandle.Close();
waitHandle = null;
}
GC.SuppressFinalize(this);
}
}
Watch in horror as IDisposable spreads
Right that's that fixed. But now FxCop will complain that Shoe creates a Shoelace, so Shoe must be IDisposable too.
And Driver creates Shoe so Driver must be IDisposable.
and Bus creates Driver so Bus must be IDisposable and so on.
Suddenly my small change to Shoelace is causing me a lot of work and my boss is wondering why I need to checkout Bus to make a change to Shoelace.
The Question
How do you prevent this spread of IDisposable, but still ensure that your unmanaged objects are properly disposed?
