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GC.SuppressFinalize(Object) Method

  • Reference

Definition

Namespace:
System
Assembly:
System.Runtime.dll
Assembly:
mscorlib.dll
Assembly:
netstandard.dll
Source:
GC.CoreCLR.cs
Source:
GC.CoreCLR.cs
Source:
GC.CoreCLR.cs

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

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

obj
Object

The object whose finalizer must not be executed.

Exceptions

ArgumentNullException

obj is null.

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.

Applies to

See also