GC.SuppressFinalize(Object) Method

public:
 static void SuppressFinalize(System::Object ^ obj);

public static void SuppressFinalize(object obj);

static member SuppressFinalize : obj -> unit

Public Shared Sub SuppressFinalize (obj As Object)

Parameters

Exceptions

Examples

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.

using System;
using System.ComponentModel;
using System.Runtime.InteropServices;

public class ConsoleMonitor : IDisposable
{
 const int STD_INPUT_HANDLE = -10;
 const int STD_OUTPUT_HANDLE = -11;
 const int STD_ERROR_HANDLE = -12;

 [DllImport("kernel32.dll", SetLastError = true)]
 static extern IntPtr GetStdHandle(int nStdHandle);

 [DllImport("kernel32.dll", SetLastError = true)]
 static extern bool WriteConsole(IntPtr hConsoleOutput, string lpBuffer,
 uint nNumberOfCharsToWrite, out uint lpNumberOfCharsWritten,
 IntPtr lpReserved);

 [DllImport("kernel32.dll", SetLastError = true)]
 static extern bool CloseHandle(IntPtr handle);

 private bool disposed = false;
 private IntPtr handle;
 private Component component;

 public ConsoleMonitor()
 {
 handle = GetStdHandle(STD_OUTPUT_HANDLE);
 if (handle == IntPtr.Zero)
 throw new InvalidOperationException("A console handle is not available.");

 component = new Component();

 string output = "The ConsoleMonitor class constructor.\n";
 uint written = 0;
 WriteConsole(handle, output, (uint) output.Length, out written, IntPtr.Zero);
 }

 // The finalizer represents Object.Finalize override.
 ~ConsoleMonitor()
 {
 if (handle != IntPtr.Zero) {
 string output = "The ConsoleMonitor finalizer.\n";
 uint written = 0;
 WriteConsole(handle, output, (uint) output.Length, out written, IntPtr.Zero);
 }
 else {
 Console.Error.WriteLine("Object finalization.");
 }
 Dispose(disposing: false);
 }

 public void Write()
 {
 string output = "The Write method.\n";
 uint written = 0;
 WriteConsole(handle, output, (uint) output.Length, out written, IntPtr.Zero);
 }

 public void Dispose()
 {
 string output = "The Dispose method.\n";
 uint written = 0;
 WriteConsole(handle, output, (uint) output.Length, out written, IntPtr.Zero);

 Dispose(disposing: true);
 GC.SuppressFinalize(this);
 }

 private void Dispose(bool disposing)
 {
 string output = String.Format("The Dispose({0}) method.\n", disposing);
 uint written = 0;
 WriteConsole(handle, output, (uint) output.Length, out written, IntPtr.Zero);

 // Execute if resources have not already been disposed.
 if (!disposed) {
 // If the call is from Dispose, free managed resources.
 if (disposing) {
 Console.Error.WriteLine("Disposing of managed resources.");
 if (component != null)
 component.Dispose();
 }
 // Free unmanaged resources.
 output = "Disposing of unmanaged resources.";
 WriteConsole(handle, output, (uint) output.Length, out written, IntPtr.Zero);

 if (handle != IntPtr.Zero) {
 if (!CloseHandle(handle))
 Console.Error.WriteLine("Handle cannot be closed.");
 }
 }
 disposed = true;
 }
}

public class Example
{
 public static void Main()
 {
 Console.WriteLine("ConsoleMonitor instance....");
 ConsoleMonitor monitor = new ConsoleMonitor();
 monitor.Write();
 monitor.Dispose();
 }
}
// 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.

open System
open System.ComponentModel
open System.Runtime.InteropServices

[<DllImport("kernel32.dll", SetLastError = true)>]
extern IntPtr GetStdHandle(int nStdHandle)

[<DllImport("kernel32.dll", SetLastError = true)>]
extern bool WriteConsole(IntPtr hConsoleOutput, string lpBuffer, uint nNumberOfCharsToWrite, uint& lpNumberOfCharsWritten, IntPtr lpReserved)

[<DllImport("kernel32.dll", SetLastError = true)>]
extern bool CloseHandle(IntPtr handle)

type ConsoleMonitor() =
 let STD_INPUT_HANDLE = -10
 let STD_OUTPUT_HANDLE = -11
 let STD_ERROR_HANDLE = -12

 let handle =
 let h = GetStdHandle STD_OUTPUT_HANDLE
 if h = IntPtr.Zero then
 raise (InvalidOperationException "A console handle is not available.")
 else
 h

 let comp = new Component()
 let output = "The ConsoleMonitor class constructor.\n"
 let mutable disposed = false
 let mutable written = 0u
 do
 WriteConsole(handle, output, uint output.Length, &written, IntPtr.Zero)
 |> ignore

 // The finalizer represents Object.Finalize override.
 override this.Finalize() =
 if handle <> IntPtr.Zero then
 let output = "The ConsoleMonitor finalizer.\n"
 let mutable written = 0u
 WriteConsole(handle, output, uint output.Length, &written, IntPtr.Zero)
 |> ignore
 else
 eprintfn "Object finalization."
 this.Dispose false

 member _.Write() =
 let output = "The Write method.\n"
 let mutable written = 0u

 WriteConsole(handle, output, uint output.Length, &written, IntPtr.Zero)
 |> ignore

 member _.Dispose(disposing: bool) =
 let output = $"The Dispose({disposing}) method.\n"
 let mutable written = 0u

 WriteConsole(handle, output, uint output.Length, &written, IntPtr.Zero)
 |> ignore

 // Execute if resources have not already been disposed.
 if not disposed then
 // If the call is from Dispose, free managed resources.
 if disposing then
 eprintfn "Disposing of managed resources."
 if comp <> null then comp.Dispose()
 // Free unmanaged resources.
 let output = "Disposing of unmanaged resources."

 WriteConsole(handle, output, uint output.Length, &written, IntPtr.Zero)
 |> ignore

 if handle <> IntPtr.Zero then
 if not (CloseHandle handle) then
 eprintfn "Handle cannot be closed."

 disposed <- true

 member this.Dispose() =
 let output = "The Dispose method.\n"
 let mutable written = 0u

 WriteConsole(handle, output, uint output.Length, &written, IntPtr.Zero)
 |> ignore

 this.Dispose true
 GC.SuppressFinalize this

 interface IDisposable with
 member this.Dispose() = this.Dispose()

printfn "ConsoleMonitor instance...."
let monitor = new ConsoleMonitor()
monitor.Write()
monitor.Dispose()

// 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.

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
 Dispose(disposing:=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(disposing:=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.

Remarks

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 or the GC has already signaled the finalizer thread to run the 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.

See also

• ReRegisterForFinalize(Object)
• Finalize()
• Dispose Pattern