Export (0) Print
Expand All

GC.SuppressFinalize Method

Requests that the common language runtime not call the finalizer for the specified object.

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

'Declaration
Public Shared Sub SuppressFinalize ( _
	obj As Object _
)

Parameters

obj
Type: System.Object

The object whose finalizer must not be executed.

ExceptionCondition
ArgumentNullException

obj is Nothing.

This method sets a bit in the object header of obj, which the runtime checks when calling finalizers. A finalizer, which is represented by the Object.Finalize method, is used to release unmanaged resources before an object is garbage-collected. If obj does not have a finalizer, the call to the SuppressFinalize method has no effect.

Objects that implement the IDisposable interface can call this method from the object's IDisposable.Dispose implementation to prevent the garbage collector from calling Object.Finalize on an object that does not require it. Typically, this is done to prevent the finalizer from releasing unmanaged resources that have already been freed by the IDisposable.Dispose implementation.

The following example demonstrates how to use the SuppressFinalize method in a resource class to prevent a redundant garbage collection from being called. The example uses the dispose pattern to free both managed resources (that is, objects that implement IDisposable) and unmanaged resources.

Imports System.ComponentModel
Imports System.Runtime.InteropServices

Public Class ConsoleMonitor
   Private Const STD_INPUT_HANDLE As Integer = -10
   Private Const STD_OUTPUT_HANDLE As Integer = -11
   Private Const STD_ERROR_HANDLE As Integer = -12

   Private Declare Function GetStdHandle Lib "kernel32" _
                            (nStdHandle As Integer) As IntPtr

   Private Declare Function WriteConsole Lib "kernel32" _
                            Alias "WriteConsoleA" _
                            (hConsoleOutput As IntPtr, lpBuffer As String,
                            nNumberOfCharsToWrite As UInteger, 
                            ByRef lpNumberOfCharsWritten As UInteger,
                            lpReserved As IntPtr) As Boolean  

   Private Declare Function CloseHandle Lib "kernel32" _ 
                           (handle As IntPtr) As Boolean 

   Private disposed As Boolean = False 
   Private handle As IntPtr
   Private component As Component

   Public Sub New()
      handle = GetStdHandle(STD_OUTPUT_HANDLE)
      If handle = IntPtr.Zero Then 
         Throw New InvalidOperationException("A console handle is not available.")
      End If

      component = new Component()

      Dim output As String = "The ConsoleMonitor class constructor." + vbCrLf
      Dim written As UInteger = 0
      WriteConsole(handle, output, CUInt(output.Length), written, IntPtr.Zero)
   End Sub 

   Protected Overrides Sub Finalize()
      If handle <> IntPtr.Zero Then 
         Dim output As String = "The ConsoleMonitor finalizer." + vbCrLf
         Dim written As UInteger = 0
         WriteConsole(handle, output, CUInt(output.Length), written, IntPtr.Zero)
      Else     
         Console.Error.WriteLine("Object finalization.")
      End If 
      ' Call Dispose with disposing = false.
      Dispose(false)
   End Sub 

   Public Sub Write()
      Dim output As String = "The Write method." + vbCrLf
      Dim written As UInteger = 0
      WriteConsole(handle, output, CUInt(output.Length), written, IntPtr.Zero)
   End Sub 

   Public Sub Dispose()
      Dim output As String =  "The Dispose method." + vbCrLf
      Dim written As UInteger = 0
      WriteConsole(handle, output, CUInt(output.Length), written, IntPtr.Zero)

      Dispose(True)
      GC.SuppressFinalize(Me) 
   End Sub 

   Private Sub Dispose(disposing As Boolean)
      Dim output As String =  String.Format("The Dispose({0}) method.{1}", 
                                            disposing, vbCrLf)
      Dim written As UInteger = 0
      WriteConsole(handle, output, CUInt(output.Length), written, IntPtr.Zero)

      ' Execute if resources have not already been disposed. 
      If Not disposed Then 
         ' If the call is from Dispose, free managed resources. 
         If disposing Then
            Console.Error.WriteLine("Disposing of managed resources.")
            If component IsNot Nothing Then component.Dispose()
         End If 
         ' Free unmanaged resources.
         output = "Disposing of unmanaged resources."
         WriteConsole(handle, output, CUInt(output.Length), written, IntPtr.Zero)

         If handle <> IntPtr.Zero Then 
            If Not CloseHandle(handle) Then
               Console.Error.WriteLine("Handle cannot be closed.")
            End If     
         End If    
      End If
      disposed = True 
   End Sub 
End Class 

Module Example
   Public Sub Main()
      Console.WriteLine("ConsoleMonitor instance....")
      Dim monitor As New ConsoleMonitor
      monitor.Write()
      monitor.Dispose()
   End Sub 
End Module 
' If the monitor.Dispose method is not called, the example displays the following output: 
'       ConsoleMonitor instance.... 
'       The ConsoleMonitor class constructor. 
'       The Write method. 
'       The ConsoleMonitor finalizer. 
'       The Dispose(False) method. 
'       Disposing of unmanaged resources. 
'        
' If the monitor.Dispose method is called, the example displays the following output: 
'       ConsoleMonitor instance.... 
'       The ConsoleMonitor class constructor. 
'       The Write method. 
'       The Dispose method. 
'       The Dispose(True) method. 
'       Disposing of managed resources. 
'       Disposing of unmanaged resources.

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

Was this page helpful?
(1500 characters remaining)
Thank you for your feedback
Show:
© 2014 Microsoft