The document discusses .NET garbage collection and provides demonstrations of how it works. It begins with an introduction on why understanding garbage collection is important. It then demonstrates garbage collection concepts like generations and finalization through code examples. The document discusses optimizations the CLR performs as well as patterns that can impact memory usage, such as circular references, singletons, and caching objects. It concludes with best practices for memory management and references for further reading.

1. Ronn BlackOctober 2010Deep Dumpster DivingA close look at .Net garbage collection

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

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

24. 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"); } }

31. 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();}

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

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

34. 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"); } }

36. 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

37. Design patterns and Memory

38. Design patterns and MemoryCircular References.FormControlControlControlControl+Controls+Parent+Parent+Parent+Parent

39. Design patterns and Memorypublic class Preferences {public Preferences instance;public static Preferences GetPrefs() {if (instance == null)instance = new Preferences(); return instance; }public event PrefsChanged;}

40. Design patterns and MemoryRooted objects (Singletons).FormControlControlControlControlPreferences+Controls+Parent+Parent+Parent+Parent$GetPrefs+PrefsChanged

41. Design patterns and MemoryLists, Hashtables, Dictionaries, etc.ControlControlControlTList<T>+Parent+Parent+Parent…

42. Design patterns and Memorypublic class Foo{public static void DoSomething() { List<Bar> bars;...//Do Somethingbar.Clear(); }}

43. Design patterns and Memorypublic class Foo{ static Dictionary<string, Bar> _bars;public static Foo() {//Initialize the Lookup table _bars = new Dictionary<string, Bar>(); _bars.Add(“EndUp”, new Bar());... }}

44. Take AwaysDon’t keep objects around unless you know you will be using them again.Save these techniques for objects that are expensive to create and are frequently used.Carefully consider use of type initializers and statics. Consider caching patterns so memory can be reclaimed if needed.If you are using observable patterns be sure you unsubscribe properly

45. 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=en (CLR Profiler for .Net 2.0)http://www.openasthra.com/multithreading/heap-overview/ (Heap Overview)http://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.aspx (Large Object Heap Uncovered)http://msdn.microsoft.com/en-us/library/aa970850.aspx (Weak Event Patterns)