CriticalFinalizerObject Class

Definition

Namespace:

System.Runtime.ConstrainedExecution

Assembly:

System.Runtime.dll

Source:

CriticalFinalizerObject.cs

Ensures that all finalization code in derived classes is marked as critical.

public ref class CriticalFinalizerObject abstract

public abstract class CriticalFinalizerObject

type CriticalFinalizerObject = class

Public MustInherit Class CriticalFinalizerObject

Inheritance

Object

CriticalFinalizerObject

Derived

System.IO.Enumeration.FileSystemEnumerator<TResult>

System.Runtime.InteropServices.CriticalHandle

System.Runtime.InteropServices.SafeHandle

System.Runtime.MemoryFailPoint

System.Threading.ReaderWriterLock

System.Threading.Thread

Examples

The following code example shows the use of the SafeFileHandle class to provide critical finalization for the standard input and output streams. The SafeFileHandle, derived from the SafeHandle class, is passed to the file stream in the FileStream constructor.

using System;
using System.Runtime.InteropServices;
using System.IO;
using Microsoft.Win32.SafeHandles;

namespace CriticalFinalizer
{
    class Program
    {
        const int STD_INPUT_HANDLE   = -10;
        const int STD_OUTPUT_HANDLE = -11;
        const int STD_ERROR_HANDLE  =  -12;
        [DllImport("Kernel32.dll", CharSet = System.Runtime.InteropServices.CharSet.Auto)]
        public static extern IntPtr GetStdHandle(int type);

        static void Main(string[] args)
        {
            FileStream fsIn = null;
            FileStream fsOut = null;
            try
            {
                SafeFileHandle sfhIn = new SafeFileHandle(GetStdHandle(STD_INPUT_HANDLE), false);
                fsIn = new FileStream(sfhIn, FileAccess.Read);
                byte[] input = new byte[] {0};
                fsIn.Read(input,0,1);
                SafeFileHandle sfhOut = new SafeFileHandle(GetStdHandle(STD_OUTPUT_HANDLE), false);
                fsOut = new FileStream(sfhOut, FileAccess.Write);
                fsOut.Write(input,0,1);
                SafeFileHandle sf = fsOut.SafeFileHandle;
            }
            finally
            {
                if (fsIn != null)
                {
                    fsIn.Close();
                    fsIn = null;
                }
                if (fsOut != null)
                {
                    fsOut.Close();
                    fsOut = null;
                }
            }
        }
    }
}

Imports System.Runtime.InteropServices
Imports System.IO
Imports Microsoft.Win32.SafeHandles

Public Module Example
   Const STD_INPUT_HANDLE As Integer  = -10
   Const STD_OUTPUT_HANDLE As Integer = -11
   Const STD_ERROR_HANDLE As Integer  = -12

   Public Declare Auto Function GetStdHandle Lib "Kernel32" (type As Integer) As IntPtr

   Public Sub Main()
      Dim fsIn As FileStream = Nothing
      Dim fsOut As FileStream = Nothing

      Try
         Dim sfhIn As New SafeFileHandle(GetStdHandle(STD_INPUT_HANDLE), False)
         fsIn = new FileStream(sfhIn, FileAccess.Read)
         Dim input() As Byte = { 0 }
         fsIn.Read(input, 0, 1)
         Dim sfhOut As New SafeFileHandle(GetStdHandle(STD_OUTPUT_HANDLE), False)
         fsOut = New FileStream(sfhOut, FileAccess.Write)
         fsOut.Write(input, 0, 1)
         Dim sf As SafeFileHandle = fsOut.SafeFileHandle
      Finally
         If fsIn IsNot Nothing Then
            fsIn.Close()
            fsIn = Nothing
         End If
         If fsOut IsNot Nothing Then 
            fsOut.Close()
            fsOut = Nothing
         End If
      End Try
   End Sub
End Module

Remarks

Classes deriving from the CriticalFinalizerObject class are implicitly treated as a constrained execution region (CER). This requires code in the finalizer to only call code with a strong reliability contract. For more information about CERs, see the System.Runtime.ConstrainedExecution namespace.

In classes derived from the CriticalFinalizerObject class, the common language runtime (CLR) guarantees that all critical finalization code will be given the opportunity to execute, provided the finalizer follows the rules for a CER, even in situations where the CLR forcibly unloads an application domain or aborts a thread. If a finalizer violates the rules for a CER, it might not successfully execute. In addition, the CLR establishes a weak ordering among normal and critical finalizers: for objects reclaimed by garbage collection at the same time, all the noncritical finalizers are called before any of the critical finalizers. For example, a class such as FileStream, which holds data in the SafeHandle class that is derived from CriticalFinalizerObject, can run a standard finalizer to flush out existing buffered data.

In most cases, you do not need to write classes that derive from the CriticalFinalizerObject class. The .NET Framework class library provides two classes, SafeHandle and CriticalHandle, that provide critical finalization functionality for handle resources. Furthermore, the .NET Framework provides a set of prewritten classes derived from the SafeHandle class, and this set is located in the Microsoft.Win32.SafeHandles namespace. These classes are designed to provide common functionality for supporting file and operating system handles.

Constructors

CriticalFinalizerObject()

Initializes a new instance of the CriticalFinalizerObject class.

Methods

Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
Finalize()	Releases all the resources used by the CriticalFinalizerObject class.
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetType()	Gets the Type of the current instance. (Inherited from Object)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
ToString()	Returns a string that represents the current object. (Inherited from Object)

See also

• SafeHandle
• CriticalHandle
• Microsoft.Win32.SafeHandles
• Constrained Execution Regions
• Reliability Best Practices