The document discusses .NET memory management and garbage collection. It begins by explaining the difference between the stack and heap, with value types stored on the stack and reference types stored on the heap. It then demonstrates how objects are allocated on the heap and referenced from the stack. The document also discusses the garbage collector and generations, and provides examples of how strings are stored. It concludes by covering unmanaged resources and the IDisposable pattern.

1. Everything* you
need to know about
.NET Memory
Ben Emmett – NDC London – 4th December 2014
*Most stuff

2. Some of what I’m
about to say is a lie

3. public void CaffeineCheck(int coffeesConsumed)
{
int coffeesRequired = 3;
CaffeineAlert alert = new CaffeineAlert();
if (coffeesConsumed < coffeesRequired)
{
alert.Announce("Send help.");
}
}

4. The Stack
CaffeineCheck (int coffeesRequired)
int coffeesRequired
int coffeesConsumed
.....
[Return address]
Alert()
CaffeineCheck()
ParentMethod()
For each thread

5. eg:
byte
int
char
Pointers
eg:
strings
classes
objects
arrays
Stack Heap

6. public void CaffeineCheck(int coffeesConsumed)
{
int coffeesRequired = 3;
CaffeineAlert alert = new CaffeineAlert();
if (coffeesConsumed < coffeesRequired)
{
CaffeineCheck(int coffeesRequired)
int coffeesRequired
int coffeesConsumed
CaffeineAlert alert
[Return address]
Stack
CaffeineAlert
alert
alert.Announce("Send help.");
}
}

7. string
Email
string
Name
Contact
list
string
Email
string
Name
Contact
list
CaffeineAlert
alert
public class CaffeineAlert
{
private List<Contact> Recipients;
CaffeineCheck(int coffeesRequired)
int coffeesRequired
int coffeesConsumed
CaffeineAlert alert
[Return address]
Stack
}
public class Contact
{
private string Name;
private string Email;
}
List<Contact>
Recipients

8. public class CaffeineAlert
{
private List<Contact> Recipients;
CaffeineCheck(int coffeesRequired)
int coffeesRequired
int coffeesConsumed
CaffeineAlert alert
[Return address]
}
public class Contact
{
private string Name;
private string Email;
}
WRONG
Stack Heap

9. public class CaffeineAlert
{
private List<Contact> Recipients;
CaffeineCheck(int coffeesRequired)
int coffeesRequired
int coffeesConsumed
CaffeineAlert alert
[Return address]
}
public class Contact
{
private string Name;
private string Email;
}
WRONG
Stack Heap

10. public class CaffeineAlert
{
private List<Contact> Recipients;
CaffeineCheck(int coffeesRequired)
int coffeesRequired
int coffeesConsumed
CaffeineAlert alert
[Return address]
}
public class Contact
{
private string Name;
private string Email;
}
WRONG
Stack Heap

11. public class CaffeineAlert
{
private List<Contact> Recipients;
CaffeineCheck(int coffeesRequired)
int coffeesRequired
int coffeesConsumed
CaffeineAlert alert
[Return address]
}
public class Contact
{
private string Name;
private string Email;
}
WRONG
Stack Heap

12. string
Email
string
Name
Contact
list
string
Email
string
Name
Contact
list
CaffeineAlert
alert
public class CaffeineAlert
{
private List<Contact> Recipients;
CaffeineCheck(int coffeesRequired)
int coffeesRequired
int coffeesConsumed
CaffeineAlert alert
[Return address]
Stack
}
public class Contact
{
private string Name;
private string Email;
}
List<Contact>
Recipients

13. CaffeineAlert
alert
List<Contact>
Recipients
String Name String Email String Name String Email

14. Object
reference
Stack

15. Object
reference
Stack

16. Object
reference
Stack

17. Object
reference
Stack

25. Small Object Heap (SOH)
The Heap
Gen 2
Gen 1
Gen 0
Large Object Heap (LOH)

26. Address
1100k
1000k
900k
800k
700k
600k
500k
400k
300k
200k
100k
0

27. Address
1100k
1000k
900k
800k
700k
600k
500k
400k
300k
200k
100k
0

28. public void NaughtyStringMessage(string name)
{
string
name
string message = "Hello ";
message += name;
Console.WriteLine(message);
NaughtyStringMessage(string name)
ref string name
[Return address]
Stack Heap
}
1
2
3
4
5
6
"Ted"

29. public void NaughtyStringMessage(string name)
{
string
name
string message = "Hello ";
message += name;
Console.WriteLine(message);
"Hello"
Stack Heap
}
string
message
1
2
3
4
5
6
"Ted"
NaughtyStringMessage(string name)
ref string message
ref string name
[Return address]

30. public void NaughtyStringMessage(string name)
{
string
name
string message = "Hello ";
message += name;
Console.WriteLine(message);
"Hello Ted"
"Hello"
Stack Heap
}
string
message
1
2
3
4
5
6
string
message
"Ted"
NaughtyStringMessage(string name)
ref string message
ref string name
[Return address]

31. public static event EventHandler UserLoggedOut;
Main form
MainForm.UserLoggedOut += HideFormData;
Child form

32. MainForm
EventHandler
UserLoggedOut
ChildForm
SecretDataWindow
Loads Of Other Junk

33. public class UnmanagedClass
{
~UnmanagedClass()
{
//Clear up the unmanaged resources
}
}

34. public class UnmanagedClass : IDisposable
{
public void Dispose()
{
//Clear up the unmanaged resources
GC.SuppressFinalize(this);
}
~UnmanagedClass()
{
this.Dispose();
}
} Not a complete IDisposable implementation

36. 2013
Most awesome 

39. Questions?
ben.emmett@red-gate.com @bcemmett slideshare.net/benemmett