I would like to add that: Calling GC.Collect() (+ WaitForPendingFinalizers()) is one part of the story. As rightly mentioned by others, GC.COllect() is non-deterministic collection and is left to the discretion of the GC itself (CLR). Even if you add a call to WaitForPendingFinalizers, it may not be deterministic. Take the code from this msdn link and run the code with the object loop iteration as 1 or 2. You will find what non-deterministic means (set a break point in the object's destructor). Precisely, the destructor is not called when there were just 1 (or 2) lingering objects by Wait..().[Citation reqd.]
If your code is dealing with unmanaged resources (ex: external file handles), you must implement destructors (or finalizers).
Here is an interesting example:
Note: If you have already tried the above example from MSDN, the following code is going to clear the air.
class Program
{
static void Main(string[] args)
{
SomePublisher publisher = new SomePublisher();
for (int i = 0; i < 10; i++)
{
SomeSubscriber subscriber = new SomeSubscriber(publisher);
subscriber = null;
}
GC.Collect();
GC.WaitForPendingFinalizers();
Console.WriteLine(SomeSubscriber.Count.ToString());
Console.ReadLine();
}
}
public class SomePublisher
{
public event EventHandler SomeEvent;
}
public class SomeSubscriber
{
public static int Count;
public SomeSubscriber(SomePublisher publisher)
{
publisher.SomeEvent += new EventHandler(publisher_SomeEvent);
}
~SomeSubscriber()
{
SomeSubscriber.Count++;
}
private void publisher_SomeEvent(object sender, EventArgs e)
{
// TODO: something
string stub = "";
}
}
I suggest, first analyze what the output could be and then run and then read the reason below:
{The destructor is only implicitly called once the program ends. } In order to deterministically clean the object, one must implement IDisposable and make an explicit call to Dispose(). That's the essence! :)