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PrepareConstrainedRegions Method

RuntimeHelpers.PrepareConstrainedRegions Method

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

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

'Declaration
Public Shared Sub PrepareConstrainedRegions

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.

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.

<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

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

  • SecurityCriticalAttribute 

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

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