This document discusses .NET garbage collection and provides examples to demonstrate how it works. It explains how the garbage collector manages memory on the managed heap, including generations and optimizations. It also demonstrates potential memory leaks and how to avoid them through proper cleanup of managed and unmanaged resources. Sample code is provided to show how to optimize performance by using the 'using' statement to dispose of objects automatically.

1. Deep Dumpster DivingA close look at .Net garbage collectionRonn BlackOctober 2009

2. Why should I care?

3. Demo 1 (Word Count)using System;usingSystem.Collections.Generic;usingSystem.Diagnostics;using System.IO;publicclassMyClass{ publicstaticvoidRunSnippet() { while(true) { Stopwatch watch = new Stopwatch();watch.Start();StreamReadersr = newStreamReader(@"C:\Users\Ronn\Documents\My Code Snippets\Garbage Collection\catcher.txt"); string text = sr.ReadToEnd();intwordCount = text.Split().Length;Console.WriteLine("{0} Words", wordCount);watch.Stop();Console.WriteLine(watch.ElapsedMilliseconds + " Milliseconds"); } }

5. using System;usingSystem.Collections.Generic;usingSystem.Threading;usingSystem.Runtime.CompilerServices;publicclassMyClass{ static Byte[] bytes; publicstaticvoidRunSnippet() { Timer tmr = new Timer(M, null, 0, 1000);Thread.Sleep(20); for(int i = 0; i < 1000; i++) bytes = new Byte[2000];Console.ReadLine(); } staticvoid M(object state) {Console.WriteLine("M - " + DateTime.Now); }Demo 2

6. Unmanaged Memory Management

7. Hi AddressUnused AreaUnused AreaArgs & VariablesStackStack PointerHeapReservedLow Address

12. NextObjPtr

13. NextObjPtr

14. RootsNextObjPtr

15. NextObjPtrRoots

16. Finalizers=~MyClass(){ //Do work here…}MyClass.Finalize(){ //Do work here…}

17. RootsFinalization QueueIIHFGEFCEFreachable QueueDCBA

18. RootsFinalization QueueI (x)I (x)H (x)FG (x)E (x)FCE (x)Freachable QueueDCB (x)A

19. RootsFinalization QueueFI (x)CFFreachable QueueE (x)DCI (x)AE (x)

20. OptimizationsGenerationsNewly created objects tend to have short lives.The older an object is, the longer it will survive. Groups objects by age and collects younger objects more frequently than older objects.All objects added to heap are in generation 0.When an object survives the first garbage collection it is promoted to generation 1.When garbage collection is triggered survivors from generation 1 are promoted to generation 2 and generation 0 survivors are promoted to gen 1.As objects "mature", they are moved to the next older generation until they reach gen 2.

21. using System;usingSystem.Collections.Generic;usingSystem.Threading;usingSystem.Runtime.CompilerServices;publicclassMyClass{ static Byte[] bytes; publicstaticvoidRunSnippet() { Timer tmr = new Timer(M, null, 0, 1000);Thread.Sleep(20); for(int i = 0; i < 1000; i++) bytes = new Byte[2000];Console.ReadLine(); } staticvoid M(object state) {Console.WriteLine("M - " + DateTime.Now); }Demo 3 – WTF??

22. Demo 4 (CLR Profile Word Count)using System;usingSystem.Collections.Generic;usingSystem.Diagnostics;using System.IO;publicclassMyClass{ publicstaticvoidRunSnippet() { while(true) { Stopwatch watch = new Stopwatch();watch.Start();StreamReadersr = newStreamReader(@"C:\Users\Ronn\Documents\My Code Snippets\Garbage Collection\catcher.txt"); string text = sr.ReadToEnd();intwordCount = text.Split().Length;Console.WriteLine("{0} Words", wordCount);watch.Stop();Console.WriteLine(watch.ElapsedMilliseconds + " Milliseconds"); } }

29. IDisposablepublic class MyClass : IDisposable{public void Dispose() { Dispose(true);GC.SuppressFinalize(this); }protected virtual void Dispose(bool disposing) {if (!disposed) {if (disposing) {// Dispose managed resources. Ex: Components.Dispose(); }// Release ONLY unmanaged resources. Ex: CloseHandle(handle); } disposed = true; }protected volatile bool disposed = false; ~MyClass() { Dispose(false); }}[ComVisible(true)]public interface IDisposable{ void Dispose();}

30. Usingusing System;using System.Collections.Generic;using System.Diagnostics;

31. Usingusing System;using System.Collections.Generic;using System.Diagnostics;using (MyClass c = new MyClass()){//Do Some Work}

32. Demo 5 - optimizeusing System;using System.Collections.Generic;using System.Diagnostics;using System.IO;public class MyClass{ public static void RunSnippet() { while(true) { Stopwatch watch = new Stopwatch();watch.Start(); using(StreamReadersr = new StreamReader(@"C:…Garbage Collection\catcher.txt")) { string line = "";intwordCount = 0; while((line = sr.ReadLine()) != null) {wordCount += line.Split().Length; }Console.WriteLine("{0} Words", wordCount); }watch.Stop();Console.WriteLine(watch.ElapsedMilliseconds + " Milliseconds"); } }

34. TotalRelocatedFinal Gen 0 Gen 1 Large Object Heap6,578,038 96,608 5,057,272 1,400,580 12 3,535,4645,473,972 101,501 1,441,201 2,097,172 103,992 9,328======== ======== ======== ========= ======== =========== -1,104,066 +4,893 -3,617,071 +696,592 +103,980 -3,526,136

35. Types of Memory LeaksManaged leaks – persistent object holds a reference to an object expected to be garbage collected.Unmanaged leaks - using unmanaged resources, dll’s or COM objects that leak memory.

39. Demo 7 - Leaky program?

45. public partial class ChildForm : Form { public ChildForm() {InitializeComponent(); } private void ChildForm_Load(object sender, EventArgs e) {Program.Skin.PropertyChanged += new PropertyChangedEventHandler(Skin_PropertyChanged); } void Skin_PropertyChanged(object sender, PropertyChangedEventArgs e) {this.BackColor = Program.Skin.BackgroundColor; this.label1.ForeColor = Program.Skin.ForegroundColor; } }

46. public partial class ChildForm : Form { public ChildForm() {InitializeComponent(); } private void ChildForm_Load(object sender, EventArgs e) {Program.Skin.PropertyChanged += new PropertyChangedEventHandler(Skin_PropertyChanged); } void Skin_PropertyChanged(object sender, PropertyChangedEventArgs e) {this.BackColor = Program.Skin.BackgroundColor; this.label1.ForeColor = Program.Skin.ForegroundColor; } protected override void OnClosing(CancelEventArgs e) {base.OnClosing(e);Program.Skin.PropertyChanged -= Skin_PropertyChanged; } }

47. Contact & Reference MaterialRonn Black rblack@btsoft.orghttp://msdn.microsoft.com/en-us/library/ms973837.aspx (Garbage Collector Basics and Performance Hints)http://www.microsoft.com/downloads/details.aspx?FamilyID=a362781c-3870-43be-8926-862b40aa0cd0&DisplayLang=enCLR Profiler for .Net 2.0http://www.openasthra.com/multithreading/heap-overview/ Heap Overviewhttp://74.125.155.132/search?q=cache:44hDjSztDf4J:doc.bughunter.net/buffer-overflow/advanced-malloc-exploits.html+malloc+overview&cd=21&hl=en&ct=clnk&gl=us Advanced Malloc exploitshttp://msdn.microsoft.com/en-us/magazine/cc534993.aspxhttp://www.microsoft.com/downloads/details.aspx?FamilyId=A362781C-3870-43BE-8926-862B40AA0CD0&displaylang=en CLR Profiler