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GC.SuppressFinalize Method

Requests that the system not call the finalizer method for the specified object.

[Visual Basic]
Public Shared Sub SuppressFinalize( _
   ByVal obj As Object _
)
[C#]
public static void SuppressFinalize(
 object obj
);
[C++]
public: static void SuppressFinalize(
 Object* obj
);
[JScript]
public static function SuppressFinalize(
   obj : Object
);

Parameters

obj
The object for which a finalizer must not be called.

Exceptions

Exception Type Condition
ArgumentNullException obj is a null reference (Nothing in Visual Basic).

Remarks

The method removes obj from the set of objects that require finalization. The obj parameter is required to be the caller of this method.

Objects that implement the IDisposable interface can call this method from the IDisposable.Dispose method to prevent the garbage collector from calling Object.Finalize on an object that does not require it.

Example

[Visual Basic] 
Imports System
Imports System.ComponentModel

' The following example demonstrates how to use the 
' GC.SuppressFinalize method in a resource class to prevent
' the clean-up code for the object from being called twice.
Public Class DisposeExample

   ' A class that implements IDisposable.
   ' By implementing IDisposable, you are announcing that 
   ' instances of this type allocate scarce resources.
   Public Class MyResource
      Implements IDisposable
      ' Pointer to an external unmanaged resource.
      Private handle As IntPtr
      ' Other managed resource this class uses.
      Private component As Component
      ' Track whether Dispose has been called.
      Private disposed As Boolean = False


      ' The class constructor initializes the handle and component.
      Public Sub New(ByVal handle As IntPtr)
         Me.handle = handle
      End Sub


      ' Implement IDisposable.
      ' Do not make this method virtual.
      ' A derived class should not be able to override this method.
      Public Overloads Sub Dispose() Implements IDisposable.Dispose
         Dispose(True)
         ' This object will be cleaned up by the Dispose method.
         ' Therefore, you should call GC.SupressFinalize to
         ' take this object off the finalization queue 
         ' and prevent finalization code for this object
         ' from executing a second time.
         GC.SuppressFinalize(Me)
      End Sub

      ' Dispose(bool disposing) executes in two distinct scenarios.
      ' If disposing equals true, the method has been called directly
      ' or indirectly by a user's code. Managed and unmanaged resources
      ' can be disposed.
      ' If disposing equals false, the method has been called by the 
      ' runtime from inside the finalizer and you should not reference 
      ' other objects. Only unmanaged resources can be disposed.
      Private Overloads Sub Dispose(ByVal disposing As Boolean)
         ' Check to see if Dispose has already been called.
         If Not Me.disposed Then
            ' If disposing equals true, dispose all managed 
            ' and unmanaged resources.
            If disposing Then
               ' Dispose managed resources.
               component.Dispose()
            End If

            ' Call the appropriate methods to clean up 
            ' unmanaged resources here.
            ' If disposing is false, 
            ' only the following code is executed.
            CloseHandle(handle)
            handle = IntPtr.Zero
         End If
         disposed = True
      End Sub

      ' Use interop to call the method necessary  
      ' to clean up the unmanaged resource.
      <System.Runtime.InteropServices.DllImport("Kernel32")> _
      Private Shared Function CloseHandle(ByVal handle As IntPtr) As [Boolean]
      End Function

      ' This finalizer will run only if the Dispose method 
      ' does not get called.
      ' It gives your base class the opportunity to finalize.
      ' Do not provide finalize methods in types derived from this class.
      Protected Overrides Sub Finalize()
         ' Do not re-create Dispose clean-up code here.
         ' Calling Dispose(false) is optimal in terms of
         ' readability and maintainability.
         Dispose(False)
         MyBase.Finalize()
      End Sub
   End Class

Public Shared Sub Main()
   ' Insert code here to create
   ' and use a MyResource object.
End Sub
End Class

[C#] 
using System;
using System.ComponentModel;

// The following example demonstrates how to use the 
// GC.SuppressFinalize method in a resource class to prevent
// the clean-up code for the object from being called twice.

public class DisposeExample
{
    // A class that implements IDisposable.
    // By implementing IDisposable, you are announcing that 
    // instances of this type allocate scarce resources.
    public class MyResource: IDisposable
    {
        // Pointer to an external unmanaged resource.
        private IntPtr handle;
        // Other managed resource this class uses.
        private Component component = new Component();
        // Track whether Dispose has been called.
        private bool disposed = false;

        // The class constructor.
        public MyResource(IntPtr handle)
        {
            this.handle = handle;
        }

        // Implement IDisposable.
        // Do not make this method virtual.
        // A derived class should not be able to override this method.
        public void Dispose()
        {
            Dispose(true);
            // This object will be cleaned up by the Dispose method.
            // Therefore, you should call GC.SupressFinalize to
            // take this object off the finalization queue 
            // and prevent finalization code for this object
            // from executing a second time.
            GC.SuppressFinalize(this);
        }

        // Dispose(bool disposing) executes in two distinct scenarios.
        // If disposing equals true, the method has been called directly
        // or indirectly by a user's code. Managed and unmanaged resources
        // can be disposed.
        // If disposing equals false, the method has been called by the 
        // runtime from inside the finalizer and you should not reference 
        // other objects. Only unmanaged resources can be disposed.
        private void Dispose(bool disposing)
        {
            // Check to see if Dispose has already been called.
            if(!this.disposed)
            {
                // If disposing equals true, dispose all managed 
                // and unmanaged resources.
                if(disposing)
                {
                    // Dispose managed resources.
                    component.Dispose();
                }
         
                // Call the appropriate methods to clean up 
                // unmanaged resources here.
                // If disposing is false, 
                // only the following code is executed.
                CloseHandle(handle);
                handle = IntPtr.Zero;            
            }
            disposed = true;         
        }

        // Use interop to call the method necessary  
        // to clean up the unmanaged resource.
        [System.Runtime.InteropServices.DllImport("Kernel32")]
        private extern static Boolean CloseHandle(IntPtr handle);

        // Use C# destructor syntax for finalization code.
        // This destructor will run only if the Dispose method 
        // does not get called.
        // It gives your base class the opportunity to finalize.
        // Do not provide destructors in types derived from this class.
        ~MyResource()      
        {
            // Do not re-create Dispose clean-up code here.
            // Calling Dispose(false) is optimal in terms of
            // readability and maintainability.
            Dispose(false);
        }
    }

    public static void Main()
    {
        // Insert code here to create
        // and use a MyResource object.
    }
}

[C++] 
#using <mscorlib.dll>
#using <System.dll>

using namespace System;
using namespace System::ComponentModel;

// The following example demonstrates how to use the
// GC::SuppressFinalize method in a resource class to prevent
// the clean up code for the object from being called twice.

// A class that implements IDisposable.
// By implementing IDisposable, you are announcing that
// instances of this type allocate scarce resources.
public __gc class MyResource : public IDisposable {
   // Pointer to an external unmanaged resource.
private:
   IntPtr handle;
   // Other managed resource this class uses.
   Component*  component;
   // Track whether Dispose has been called.
   bool  disposed;

public:
   // The class constructor.
   MyResource(IntPtr handle) {
      this->handle = handle;
      disposed = false;
   }

   // Implement IDisposable.
   // Do not make this method virtual.
   // A derived class should not be able to  this method.
   void Dispose() {
      Dispose(true);
      // This object will be cleaned up by the Dispose method.
      // Therefore, you should call GC::SupressFinalize to
      // take this object off the finalization queue
      // and prevent finalization code for this object
      // from executing a second time.
      GC::SuppressFinalize(this);
   }

private:
   // Dispose(bool disposing) executes in two distinct scenarios.
   // If disposing equals true, the method has been called directly
   // or indirectly by a user's code. Managed and unmanaged resources
   // can be disposed.
   // If disposing equals false, the method has been called by the
   // runtime from inside the finalizer and you should not reference
   // other objects. Only unmanaged resources can be disposed.
   void Dispose(bool disposing) {
      // Check to see if Dispose has already been called.
      if (!this->disposed) {
         // If disposing equals true, dispose all managed
         // and unmanaged resources.
         if (disposing) {
            // Dispose managed resources.
            component->Dispose();
         }

         // Call the appropriate methods to clean up
         // unmanaged resources here.
         // If disposing is false,
         // only the following code is executed.
         CloseHandle(handle);
         handle = IntPtr::Zero;
      }
      disposed = true;
   }

   // Use interop to call the method necessary
   // to clean up the unmanaged resource.
   [System::Runtime::InteropServices::DllImport(S"Kernel32")]
   static Boolean CloseHandle(IntPtr handle);

   // Use C# destructor syntax for finalization code.
   // This destructor will run only if the Dispose method
   // does not get called.
   // It gives your base class the opportunity to finalize.
   // Do not provide destructors in types derived from this class.
   ~MyResource() {
      // Do not re-create Dispose clean-up code here.
      // Calling Dispose(false) is optimal in terms of
      // readability and maintainability.
      Dispose(false);
   }
};

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework, Common Language Infrastructure (CLI) Standard

See Also

GC Class | GC Members | System Namespace | ReRegisterForFinalize

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