GC.Collect Method (Int32) (System)

Switch View :

Classic

Lightweight

ScriptFree

Site Feedback

.NET Framework Class Library

GC.Collect Method (Int32)

Forces garbage collection from generation zero through a specified generation.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

Syntax

Visual Basic (Declaration)

Public Shared Sub Collect ( _
	generation As Integer _
)

Visual Basic (Usage)

Dim generation As Integer

GC.Collect(generation)

public static void Collect (
	int generation
)

C++

public:
static void Collect (
	int generation
)

public static void Collect (
	int generation
)

JScript

public static function Collect (
	generation : int
)

Parameters

generation: The number of the oldest generation on which garbage collection can be performed.

Exceptions

Exception type	Condition
ArgumentOutOfRangeException	generation is less than 0.

Remarks

Use this method to attempt to reclaim memory that is inaccessible. However, use of this method does not guarantee that all inaccessible memory in the specified generation is reclaimed.

If object aging is implemented, the garbage collector does not collect objects with a generation number higher than the specified generation. If object aging is not implemented, the garbage collector considers all objects during the garbage collection.

Use the MaxGeneration property to determine the maximum valid value of generation.

To have the garbage collector consider all objects regardless of their generation, use the version of this method that takes no arguments.

Performance Considerations

A garbage collection operation for generations 0 and 1 is relatively fast and requires few system resources. In contrast, a garbage collection operation for generation 2 is a lengthy activity that pauses the application process while the garbage collector examines every object on the heap. The garbage collection mechanism is very efficient because it observes the way memory is being allocated in the system, and tunes its behavior accordingly. Attempting to force a garbage collection operation by calling the Collect or WaitForPendingFinalizers method interferes with the garbage collection algorithm and usually worsens your application's memory usage.

Call the Collect method only when you know your application is finished using a significant amount of memory that is allocated only once. For example, call the Collect method when your application has finished using a large cache, or when a large dialog is closed and you know, or it is unlikely, that the dialog will be reopened.

Example

Visual Basic

Imports System

Namespace GCCollectInt_Example
    Class MyGCCollectClass
        Private maxGarbage As Long = 10000

        Public Shared Sub Main()
            Dim myGCCol As New MyGCCollectClass

            'Determine the maximum number of generations the system
            'garbage collector currently supports.
            Console.WriteLine("The highest generation is {0}", GC.MaxGeneration)

            myGCCol.MakeSomeGarbage()

            'Determine which generation myGCCol object is stored in.
            Console.WriteLine("Generation: {0}", GC.GetGeneration(myGCCol))

            'Determine the best available approximation of the number 
            'of bytes currently allocated in managed memory.
            Console.WriteLine("Total Memory: {0}", GC.GetTotalMemory(False))

            'Perform a collection of generation 0 only.
            GC.Collect(0)

            'Determine which generation myGCCol object is stored in.
            Console.WriteLine("Generation: {0}", GC.GetGeneration(myGCCol))

            Console.WriteLine("Total Memory: {0}", GC.GetTotalMemory(False))

            'Perform a collection of all generations up to and including 2.
            GC.Collect(2)

            'Determine which generation myGCCol object is stored in.
            Console.WriteLine("Generation: {0}", GC.GetGeneration(myGCCol))
            Console.WriteLine("Total Memory: {0}", GC.GetTotalMemory(False))
            Console.Read()

        End Sub


        Sub MakeSomeGarbage()
            Dim vt As Version

            Dim i As Integer
            For i = 0 To maxGarbage - 1
                'Create objects and release them to fill up memory
                'with unused objects.
                vt = New Version
            Next i
        End Sub
    End Class
End Namespace

using System;

namespace GCCollectIntExample
{
    class MyGCCollectClass
    {
        private const long maxGarbage = 1000;
      
        static void Main()
        {
            MyGCCollectClass myGCCol = new MyGCCollectClass();

            // Determine the maximum number of generations the system
	    // garbage collector currently supports.
            Console.WriteLine("The highest generation is {0}", GC.MaxGeneration);
            
            myGCCol.MakeSomeGarbage();

            // Determine which generation myGCCol object is stored in.
            Console.WriteLine("Generation: {0}", GC.GetGeneration(myGCCol));
            
            // Determine the best available approximation of the number 
	    // of bytes currently allocated in managed memory.
            Console.WriteLine("Total Memory: {0}", GC.GetTotalMemory(false));
            
            // Perform a collection of generation 0 only.
            GC.Collect(0);
            
            // Determine which generation myGCCol object is stored in.
            Console.WriteLine("Generation: {0}", GC.GetGeneration(myGCCol));
            
            Console.WriteLine("Total Memory: {0}", GC.GetTotalMemory(false));
            
            // Perform a collection of all generations up to and including 2.
            GC.Collect(2);
            
            // Determine which generation myGCCol object is stored in.
            Console.WriteLine("Generation: {0}", GC.GetGeneration(myGCCol));
            Console.WriteLine("Total Memory: {0}", GC.GetTotalMemory(false));
            Console.Read();
        }

        void MakeSomeGarbage()
        {
            Version vt;

            for(int i = 0; i < maxGarbage; i++)
            {
                // Create objects and release them to fill up memory
		// with unused objects.
                vt = new Version();
            }
        }
    }
}

C++

using namespace System;
const long maxGarbage = 1000;
ref class MyGCCollectClass
{
public:
   void MakeSomeGarbage()
   {
      Version^ vt;
      for ( int i = 0; i < maxGarbage; i++ )
      {
         
         // Create objects and release them to fill up memory
         // with unused objects.
         vt = gcnew Version;

      }
   }

};

int main()
{
   MyGCCollectClass^ myGCCol = gcnew MyGCCollectClass;
   
   // Determine the maximum number of generations the system
   // garbage collector currently supports.
   Console::WriteLine( "The highest generation is {0}", GC::MaxGeneration );
   myGCCol->MakeSomeGarbage();
   
   // Determine which generation myGCCol object is stored in.
   Console::WriteLine( "Generation: {0}", GC::GetGeneration( myGCCol ) );
   
   // Determine the best available approximation of the number
   // of bytes currently allocated in managed memory.
   Console::WriteLine( "Total Memory: {0}", GC::GetTotalMemory( false ) );
   
   // Perform a collection of generation 0 only.
   GC::Collect( 0 );
   
   // Determine which generation myGCCol object is stored in.
   Console::WriteLine( "Generation: {0}", GC::GetGeneration( myGCCol ) );
   Console::WriteLine( "Total Memory: {0}", GC::GetTotalMemory( false ) );
   
   // Perform a collection of all generations up to and including 2.
   GC::Collect( 2 );
   
   // Determine which generation myGCCol object is stored in.
   Console::WriteLine( "Generation: {0}", GC::GetGeneration( myGCCol ) );
   Console::WriteLine( "Total Memory: {0}", GC::GetTotalMemory( false ) );
}

package GCCollectIntExample; 

import System.* ;

class MyGCCollectClass
{
    private static final long maxGarbage = 1000;

    public static void main(String[] args)
    {
        MyGCCollectClass myGCCol = new MyGCCollectClass();

        // Determine the maximum number of generations the system
        // garbage collector currently supports.
        Console.WriteLine("The highest generation is {0}", 
            System.Convert.ToString(GC.get_MaxGeneration()));
        myGCCol.MakeSomeGarbage();

        // Determine which generation myGCCol object is stored in.
        Console.WriteLine("Generation: {0}", 
            System.Convert.ToString(GC.GetGeneration(myGCCol)));

        // Determine the best available approximation of the number 
        // of bytes currently allocated in managed memory.
        Console.WriteLine("Total Memory: {0}", 
            System.Convert.ToString(GC.GetTotalMemory(false)));

        // Perform a collection of generation 0 only.
        GC.Collect(0);

        // Determine which generation myGCCol object is stored in.
        Console.WriteLine("Generation: {0}", 
            System.Convert.ToString(GC.GetGeneration(myGCCol)));
        Console.WriteLine("Total Memory: {0}", 
            System.Convert.ToString(GC.GetTotalMemory(false)));

        // Perform a collection of all generations up to and including 2.
        GC.Collect(2);

        // Determine which generation myGCCol object is stored in.
        Console.WriteLine("Generation: {0}", 
            System.Convert.ToString(GC.GetGeneration(myGCCol)));
        Console.WriteLine("Total Memory: {0}", 
            System.Convert.ToString(GC.GetTotalMemory(false)));
        Console.Read();
    } //main

    void MakeSomeGarbage()
    {
        Version vt;

        for (int i = 0; i < maxGarbage; i++) {
            // Create objects and release them to fill up memory
            // with unused objects.
            vt = new Version();
        }
    } //MakeSomeGarbage
} //MyGCCollectClass

Platforms

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

Version Information

.NET Framework

Supported in: 2.0, 1.1, 1.0

Reference

GC Class
GC Members
System Namespace