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 ()
public static void PrepareConstrainedRegions ()
public static function PrepareConstrainedRegions ()
Not applicable.

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)]
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;
    }


Windows 98, Windows Server 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 Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0

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