Receiving notifications when garbage collections occur

While creating the 3rd Edition of my CLR via C# book (http://www.amazon.com/CLR-via-C-Third-Pro-Developer/dp/0735627045/ref=dp_ob_title_bk), I came up with a cool little class that will raise an event after a collection of Generation 0 or Generation 2 occurs. Here is the code for the class:

public static class GCNotification {
private static Action<Int32> s_gcDone = null; // The event’s field
public static event Action<Int32> GCDone {
add {
// If there were no registered delegates before, start reporting notifications now
if (s_gcDone == null) { new GenObject(0); new GenObject(2); }
s_gcDone += value;
}
remove { s_gcDone -= value; }
}
private sealed class GenObject {
private Int32 m_generation;
public GenObject(Int32 generation) { m_generation = generation; }
~GenObject() { // This is the Finalize method
// If this object is in the generation we want (or higher),
// notify the delegates that a GC just completed
if (GC.GetGeneration(this) >= m_generation) {
Action<Int32> temp = Interlocked.CompareExchange(ref s_gcDone, null, null);
if (temp != null) temp(m_generation);
}
         // Keep reporting notifications if there is at least one delegate
// registered, the AppDomain isn’t unloading, and the process
// isn’t shutting down
if ((s_gcDone != null) &&
!AppDomain.CurrentDomain.IsFinalizingForUnload() &&
!Environment.HasShutdownStarted) {
// For Gen 0, create a new object; for Gen 2, resurrect the
// object & let the GC call Finalize again the next time Gen 2 is GC’d
if (m_generation == 0) new GenObject(0);
else GC.ReRegisterForFinalize(this);
} else { /* Let the objects go away */ }
}
}
}

And here is some code to see it in action:

 

public static void Main() {
GCNotification.GCDone += g => Console.Beep(g == 0 ? 800 : 8000, 200);
var l = new List<Object>();
// Construct a lot of 100-byte objects.
for (Int32 x = 0; x < 1000000; x++) {
Console.WriteLine(x);
Byte[] b = new Byte[100];
l.Add(b);
}
}

 

This gives you a very small taste of what you should expect to see in the next edition of my book. Hope you enjoy.