The PrepareConstrainedRegions method marks catch, finally, and fault blocks as constrained execution regions (CERs). Code that is marked as a constrained region must call only other code with strong reliability contracts. It should not allocate or make virtual calls to unprepared or unreliable methods unless it is prepared to handle failures.

Note that no intermediate language opcodes, except NOP, are allowed between a call to the PrepareConstrainedRegions method and the try block. For more information about CERs, see the classes in the System.Runtime.ConstrainedExecution namespace.

CERs marked using the PrepareConstrainedRegions method do not work perfectly when a StackOverflowException is generated from the try block. For more information see the ExecuteCodeWithGuaranteedCleanup method.

The PrepareConstrainedRegions method calls the ProbeForSufficientStack method.

The following code example shows how to reliably set handles using the PrepareConstrainedRegions method. To reliably set a handle to a specified pre-existing handle, you must ensure that the allocation of the native handle and the subsequent recording of that handle within a SafeHandle object is atomic. Any failure between these operations (such as a thread abort or out of memory exception) will result in the native handle being leaked. You can use the PrepareConstrainedRegions method to make sure that the handle is not leaked.

<StructLayout(LayoutKind.Sequential)> _
Structure MyStruct
    Public m_outputHandle As IntPtr
End Structure 'MyStruct


NotInheritable Class MySafeHandle
    Inherits SafeHandle

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

    End Sub


    Public Function AllocateHandle() As MySafeHandle
        ' Allocate SafeHandle first to avoid failure later.
        Dim sh As New MySafeHandle()

        RuntimeHelpers.PrepareConstrainedRegions()
        Try
        Finally
            Dim myStruct As New MyStruct()
            NativeAllocateHandle(myStruct)
            sh.SetHandle(myStruct.m_outputHandle)
        End Try

        Return sh

    End Function

• SecurityPermission 

  for permission to call unmanaged code. Associated enumeration: UnmanagedCode Security action: LinkDemand

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

.NET Framework

Reference