Jeffrey Richter: Receiving notifications when garbage collections occur

Jeffrey Richter here. While creating the 3rd Edition of my CLR via C# book, 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++) {
Byte[] b = new Byte[100];

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

Devon here. This post was originally published on Jeffrey’s blog, which you can find here. Also, Jeffrey’s new CLR via C# book will be available in mid-February, and its ISBN is 9780735627048. We’ll post much more about the book, including some original posts from Jeffrey (we hope), in the coming weeks.