RuntimeHelpers.PrepareConstrainedRegions Method


Designates a body of code as a constrained execution region (CER).

 static void PrepareConstrainedRegions();
public static void PrepareConstrainedRegions ();
static member PrepareConstrainedRegions : unit -> unit
Public Shared Sub PrepareConstrainedRegions ()


The following example shows how to reliably set handles by 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.

struct MyStruct
    public IntPtr m_outputHandle;

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

    public MySafeHandle AllocateHandle()
        // Allocate SafeHandle first to avoid failure later.
        MySafeHandle sh = new MySafeHandle();

        try { }
            MyStruct myStruct = new MyStruct();
            NativeAllocateHandle(ref myStruct);

        return sh;

<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()

            Dim myStruct As New MyStruct()
        End Try

        Return sh

    End Function


Compilers use this method to mark catch, finally, and fault blocks as constrained execution regions (CERs). Code that is marked as a constrained region must only call 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 that are 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.


requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.

Applies to