Garbage collection in .net (basic level)

GARBAGE COLLECTION IN .NET
(BASIC LEVEL)
Larry Nung

AGENDA
Function
Feature
Managed Heap
Small Object Heap (SOH)
Large Object Heap (LOH)
Collection With Finalization Queue
Collection Timing
Strong reference & Week reference
GC Mode
Reference
Q & A 3

FUNCTION
 Automatic memory management
 Responsible for reclaiming the memory of no longer used objects.
5

FEATURE
 Allow us to develop an application without having
worry to free memory.
 Allocates memory for objects efficiently on the
managed heap.
 Reclaims the memory for no longer used objects
and keeps the free memory for future allocations.
 Provides memory safety by making sure that an
object cannot use the content of another object.
7

MANAGED HEAP
 A series of allocated memory segments (approx
16Mb in size each) to store and manage objects
9

GENERATIONS
 Generation 0
 The youngest generation and contains short-lived
objects.
 About 256 KB
 Generation 1
 Contains short-lived objects and serves as a buffer
between short-lived objects and long-lived objects.
 About 2MB
 Generation 2.
 Contains long-lived objects.
 About 10MB
11

PROMOTIONS
 Objects that are not reclaimed in a garbage
collection are known as survivors, and are
promoted to the next generation.
12

LARGE OBJECT HEAP (LOH)
 Feature
 Never compacts
14

COLLECTION WITH FINALIZATION
QUEUE
16

COLLECTION WITH FINALIZATION QUEUE
17

18

19

20

COLLECTION TIMING
 Low physical memory.
 The memory allocated on the managed heap
surpasses an acceptable threshold.
 Invoke System.GC.Collect.
22

STRONG REFERENCE & WEEK
REFERENCE
23

STRONG REFERENCE & WEEK REFERENCE
 Week reference
 A reference that does not protect the referenced object
from collection by a garbage collector.
24

STRONG REFERENCE & WEEK REFERENCE
using System;
public class Program {
public static void Main() {
var person1 = new Person("Larry");
var person2 = new WeakReference(null);
person2.Target = new Person("Jack");
GC.Collect();
var jack = person2.Target as Person;
Console.WriteLine(person1.Name);
Console.WriteLine(jack == null ? "(null)" : jack.Name);
}
}
public class Person {
public string Name { get; private set; }
public Person(string name) {
this.Name = name;
}
}
25
person1
person2
Larry
Heap
Jack
Strong Reference
Week Reference
person1 Larry
Heap
Strong Reference
GC

GC MODE
 Workstation GC
 Default GC mode.
 Server GC
 Available only on multiprocessor computers.
 Creates a separate managed heap and thread for each
processor and performs collections in parallel.
 ASP.NET and SQL Server enable.
27

REFERENCE
 Garbage Collection
 https://msdn.microsoft.com/en-
us/library/0xy59wtx(v=vs.110).aspx
 .NET 的自動記憶體管理
 https://msdn.microsoft.com/zh-
tw/library/dd229208.aspx?f=255&MSPPError=-
2147217396
 .Net Garbage Collection in depth
 http://www.dotnet-
tricks.com/Tutorial/netframework/0L3P131012-.Net-
Garbage-Collection-in-depth.html
29

REFERENCE
 Understanding .NET Garbage Collection
 http://www.telerik.com/blogs/understanding-net-
garbage-collection
30

Garbage collection in .net (basic level)

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