GC.GetGeneration Method

Definition

Namespace:

System

Assemblies:

netstandard.dll, System.Runtime.dll

Returns the current generation number of an object.

Overloads

GetGeneration(Object)	Returns the current generation number of the specified object.
GetGeneration(WeakReference)	Returns the current generation number of the target of a specified weak reference.

GetGeneration(Object)

Source:

GC.cs

Returns the current generation number of the specified object.

C#

public static int GetGeneration(object obj);

Parameters

obj

Object

The object that generation information is retrieved for.

Returns

Int32

The current generation number of obj, or Int32.MaxValue.

Examples

The following example demonstrates how to use the GetGeneration method to determine the age of an object. The example then performs garbage collections to clean up memory and compare the pre and post collection memory totals in the console.

C#

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();
            }
        }
    }
}

Remarks

Use this method to determine the age of an object, and then use that information with the Collect method to force the garbage collector to collect objects in the same generation. For example, use this method when you have a set of objects that are created as a group and that become inaccessible at the same time.

Starting in .NET 8, this method might return MaxValue for objects allocated on non-GC heaps. For more information, see GC.GetGeneration might return Int32.MaxValue.

See also

• MaxGeneration

GetGeneration(WeakReference)

Source:

GC.CoreCLR.cs

Returns the current generation number of the target of a specified weak reference.

C#

public static int GetGeneration(WeakReference wo);

Parameters

wo

WeakReference

A WeakReference that refers to the target object whose generation number is to be determined.

Returns

Int32

The current generation number of the target of wo, or MaxValue.

Exceptions

ArgumentException

Garbage collection has already been performed on wo.

ArgumentNullException

The target of the weak reference has already been garbage collected.

Examples

The following example demonstrates the use of the GetGeneration method to determine the age of a weak reference object.

C#

using System;

namespace GCGetGenerationWeakExample
{
    public class MyGCCollectClass
    {
        private const long maxGarbage = 1000;

        static void Main()
        {
            // Create a strong reference to an object.
            MyGCCollectClass myGCCol = new MyGCCollectClass();

            // Put some objects in memory.
            myGCCol.MakeSomeGarbage();

            // Get the generation of managed memory where myGCCol is stored.
            Console.WriteLine("The object is in generation: {0}", GC.GetGeneration(myGCCol));
                        
            // Perform a full garbage collection.
            // Because there is a strong reference to myGCCol, it will
            // not be garbage collected.
            GC.Collect();
            
            // Get the generation of managed memory where myGCCol is stored.
            Console.WriteLine("The object is in generation: {0}", GC.GetGeneration(myGCCol));
            
            // Create a WeakReference to myGCCol.
            WeakReference wkref = new WeakReference(myGCCol);
            // Remove the strong reference to myGCCol.
            myGCCol = null;

            // Get the generation of managed memory where wkref is stored.
            Console.WriteLine("The WeakReference to the object is in generation: {0}", GC.GetGeneration(wkref));
            
            // Perform another full garbage collection.
            // A WeakReference will not survive a garbage collection.
            GC.Collect();
        
            // Try to get the generation of managed memory where wkref is stored.
            // Because it has been collected, an exception will be thrown.
            try
            {
                Console.WriteLine("The WeakReference to the object is in generation: {0}", GC.GetGeneration(wkref));
                Console.Read();
            }
            catch(Exception e)
            {
                Console.WriteLine("The WeakReference to the object has been garbage collected: '{0}'", e);
                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();
            }
        }
    }
}

Remarks

Starting in .NET 8, this method might return MaxValue for objects allocated on non-GC heaps. For more information, see GC.GetGeneration might return Int32.MaxValue.

See also

• MaxGeneration