FixedAddressValueTypeAttribute Class
 
System_CAPS_noteNote

The .NET API Reference documentation has a new home. Visit the .NET API Browser on docs.microsoft.com to see the new experience.

Fixes the address of a static value type field throughout its lifetime. This class cannot be inherited.

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

SystemObject
   SystemAttribute
    System.Runtime.CompilerServicesFixedAddressValueTypeAttribute

[SerializableAttribute]
[AttributeUsageAttribute(AttributeTargets.Field)]
public sealed class FixedAddressValueTypeAttribute : Attribute
[SerializableAttribute]
[AttributeUsageAttribute(AttributeTargets::Field)]
public ref class FixedAddressValueTypeAttribute sealed : Attribute
[<Sealed>]
[<SerializableAttribute>]
[<AttributeUsageAttribute(AttributeTargets.Field)>]
type FixedAddressValueTypeAttribute = 
    class
        inherit Attribute
    end
<SerializableAttribute>
<AttributeUsageAttribute(AttributeTargets.Field)>
Public NotInheritable Class FixedAddressValueTypeAttribute
	Inherits Attribute
NameDescription
System_CAPS_pubmethod FixedAddressValueTypeAttribute

Initializes a new instance of the FixedAddressValueTypeAttribute class.

NameDescription
System_CAPS_pubproperty

When implemented in a derived class, gets a unique identifier for this Attribute.(Inherited from Attribute.)

NameDescription
System_CAPS_pubmethod Equals

This API supports the product infrastructure and is not intended to be used directly from your code. Returns a value that indicates whether this instance is equal to a specified object.(Inherited from Attribute.)

System_CAPS_pubmethod GetHashCode

Returns the hash code for this instance.(Inherited from Attribute.)

System_CAPS_pubmethod GetType

Gets the Type of the current instance.(Inherited from Object.)

System_CAPS_pubmethod IsDefaultAttribute

When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class.(Inherited from Attribute.)

System_CAPS_pubmethod Match

When overridden in a derived class, returns a value that indicates whether this instance equals a specified object.(Inherited from Attribute.)

System_CAPS_pubmethod ToString

Returns a string that represents the current object.(Inherited from Object.)

NameDescription
System_CAPS_pubinterface System_CAPS_privmethod _AttributeGetIDsOfNames

Maps a set of names to a corresponding set of dispatch identifiers.(Inherited from Attribute.)

System_CAPS_pubinterface System_CAPS_privmethod _AttributeGetTypeInfo

Retrieves the type information for an object, which can be used to get the type information for an interface.(Inherited from Attribute.)

System_CAPS_pubinterface System_CAPS_privmethod _AttributeGetTypeInfoCount

Retrieves the number of type information interfaces that an object provides (either 0 or 1).(Inherited from Attribute.)

System_CAPS_pubinterface System_CAPS_privmethod _AttributeInvoke

Provides access to properties and methods exposed by an object.(Inherited from Attribute.)

Use the FixedAddressValueTypeAttribute attribute to mark static value types as pinned upon creation.

This attribute is used by the Microsoft Visual C++ compiler.

Static value type fields are created as boxed objects. This means that their address can change as garbage collection is performed. When you apply this attribute to a static value type, its address remains constant during its lifetime.

The following example illustrates the use of the FixedAddressValueTypeAttribute attribute to pin a static field in memory. It defines an Age structure and initializes two classes that have static fields of type Age. The second class applies FixedAddressValueTypeAttribute to pin the field's address. A number of memory allocations are made before and after these two objects are instantiated and the garbage collector is invoked. The output from the example shows that although the address of the first Age field has changed after garbage collection, the address of the field to which FixedAddressValueTypeAttribute is applied has not.

using System;
using System.Runtime.CompilerServices;

public struct Age {
   public int years;
   public int months;
}

public class FreeClass
{
   public static Age FreeAge;

   public static unsafe IntPtr AddressOfFreeAge()
   { 
      fixed (Age* pointer = &FreeAge) 
      { return (IntPtr) pointer; } 
   }
}

public class FixedClass
{
   [FixedAddressValueType]
   public static Age FixedAge;

   public static unsafe IntPtr AddressOfFixedAge()
   { 
      fixed (Age* pointer = &FixedAge) 
      { return (IntPtr) pointer; } 
   }   
}

public class Example
{
   public static void Main()
   {
      AllocateMemory();

      // Get addresses of static Age fields.
      IntPtr freePtr1 = FreeClass.AddressOfFreeAge();
      AllocateMemory();

      IntPtr fixedPtr1 = FixedClass.AddressOfFixedAge();
      AllocateMemory();

      // Garbage collection.
      GC.Collect();
      GC.WaitForPendingFinalizers();

      // Get addresses of static Age fields after garbage collection.
      IntPtr freePtr2 = FreeClass.AddressOfFreeAge();
      IntPtr fixedPtr2 = FixedClass.AddressOfFixedAge();

      // Display addresses before and after garbage collection
      Console.WriteLine("Normal static: {0} -> {1}", freePtr1, freePtr2);
      Console.WriteLine("Pinned static:  {0} -> {1}", fixedPtr1, fixedPtr2);  
   }

   // Allocate memory for 100,000 objects.
   static public void AllocateMemory()
   {
      for (int ctr = 0; ctr <= 100000; ctr++)
      {
         object o = new object();      
      }
   }
}
// The example displays output similar to the following:
//       Normal static: 19932420 -> 19863704
//       Pinned static:  19985508 -> 19985508
.NET Framework
Available since 2.0
Silverlight
Available since 2.0

Any public static ( Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Return to top