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RuntimeHelpers.PrepareConstrainedRegions Method

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

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

public static void 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)]
    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();

            RuntimeHelpers.PrepareConstrainedRegions();
            try { }
            finally
            {
                MyStruct myStruct = new MyStruct();
                NativeAllocateHandle(ref myStruct);
                sh.SetHandle(myStruct.m_outputHandle);
            }

            return sh;
        }

.NET Framework

Supported in: 4.5.2, 4.5.1, 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.

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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