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SafeHandle.DangerousRelease Method

Note: This method is new in the .NET Framework version 2.0.

Manually decrements the reference counter on a SafeHandle instance.

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

'Declaration
Public Sub DangerousRelease
'Usage
Dim instance As SafeHandle

instance.DangerousRelease
public void DangerousRelease ()
public function DangerousRelease ()

The DangerousRelease method is the counterpart to DangerousAddRef. You should always match a call to the DangerousRelease method with a successful call to DangerousAddRef.

Caution noteCaution

This method is intended for advanced users and must always be used carefully. To avoid leaking handle resources, always call this method inside a constrained execution region (CER), where a thread abort cannot interrupt processing. In the same way that unmatched DangerousAddRef calls can cause resource leaks, unmatched DangerousRelease calls can cause invalid handle states to become visible to other threads. Do not expose DangerousAddRef or DangerousRelease calls to untrusted code.

The following code example demonstrates how to use the DangerousAddRef, DangerousGetHandle, and DangerousRelease with a custom class called the MySafeHandle class that implements the SafeHandle class.

Imports System
Imports System.Runtime.InteropServices
Imports System.Runtime.CompilerServices
Imports System.Runtime.ConstrainedExecution
Imports System.Security.Permissions




NotInheritable Class MySafeHandle
    Inherits SafeHandle

    ' Called by P/Invoke when returning SafeHandles
    Public Sub New()
        MyBase.New(IntPtr.Zero, True)

    End Sub



    ' If & only if you need to support user-supplied handles
    Friend Sub New(ByVal preexistingHandle As IntPtr, ByVal ownsHandle As Boolean)
        MyBase.New(IntPtr.Zero, ownsHandle)
        SetHandle(preexistingHandle)

    End Sub

    ' Do not provide a finalizer - SafeHandle's critical finalizer will
    ' call ReleaseHandle for you.

    Public Overrides ReadOnly Property IsInvalid() As Boolean

        Get
            Return IsClosed OrElse handle = IntPtr.Zero
        End Get
    End Property

    <DllImport("kernel32"), ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)> _
    Private Shared Function CloseHandle(ByVal handle As IntPtr) As Boolean

    End Function


    Protected Overrides Function ReleaseHandle() As Boolean

        Return CloseHandle(handle)

    End Function


    <DllImport("kernel32")> _
    Public Shared Function CreateHandle(ByVal someState As Integer) As MySafeHandle

    End Function
End Class





Public Class Example

    Shared Sub Main()

    	Run()

    End Sub

    <SecurityPermission(SecurityAction.Demand, UnmanagedCode:=true)> _
    shared Sub Run()

        'Create an instance of MySafeHandle.
        Dim myHandle As New MySafeHandle()

        ' ...Set the handle...

        Dim mustRelease As Boolean = False
        RuntimeHelpers.PrepareConstrainedRegions()
        Try
            myHandle.DangerousAddRef(mustRelease)
            Dim handleCopy As IntPtr = myHandle.DangerousGetHandle()
            ' ... perform operations with handleCopy ...
        Finally
            If mustRelease Then
                myHandle.DangerousRelease()
            End If
        End Try    	
  
    End Sub
End Class


Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0

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