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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)

public void 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.

using System;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;
using System.Runtime.ConstrainedExecution;
using System.Security.Permissions;

namespace SafeHandleExample
{

    sealed class MySafeHandle : SafeHandle
    {
        // Called by P/Invoke when returning SafeHandles
        public MySafeHandle()
            : base(IntPtr.Zero, true)
        {
        }

        
        // If & only if you need to support user-supplied handles
        internal MySafeHandle(IntPtr preexistingHandle, bool ownsHandle)
            : base(IntPtr.Zero, ownsHandle)
        {
            SetHandle(preexistingHandle);
        }

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

        public override bool IsInvalid
        {

            get { return IsClosed || handle == IntPtr.Zero; }
        }
   
        [DllImport("kernel32")]
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
        private static extern bool CloseHandle(IntPtr handle);

        protected override bool ReleaseHandle()
        {
            return CloseHandle(handle);
        }

        [DllImport("kernel32")]
        public static extern MySafeHandle CreateHandle(int someState);


    }


    public class Example
    {
        static void Main()
        {
		Run();

        }

        [SecurityPermission(SecurityAction.Demand, UnmanagedCode=true)]
        static void Run()
        {
            //Create an instance of MySafeHandle.
            MySafeHandle myHandle = new MySafeHandle();

            // ...Set the handle...
       

            bool mustRelease = false;
            RuntimeHelpers.PrepareConstrainedRegions();
            try
            {
                myHandle.DangerousAddRef(ref mustRelease);
                IntPtr handleCopy = myHandle.DangerousGetHandle();
                // ... perform operations with handleCopy ...
            }
            finally
            {
                if (mustRelease)
                    myHandle.DangerousRelease();
            }

        }
    }

    
}

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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