System.Threading.AsyncFlowControl.Undo C# (CSharp) Method

        public void Undo()
        {
            if (_thread == null)
            {
                throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_CannotUseAFCMultiple"));
            }  
            if (_thread != Thread.CurrentThread)
            {
                throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_CannotUseAFCOtherThread"));
            }
            if (useEC) 
            {
                if (Thread.CurrentThread.ExecutionContext != _ec)
                {
                    throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_AsyncFlowCtrlCtxMismatch"));
                }      
                ExecutionContext.RestoreFlow();
            }
            else
            {
                if (Thread.CurrentThread.ExecutionContext.SecurityContext != _sc)
                {
                    throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_AsyncFlowCtrlCtxMismatch"));
                }      
                SecurityContext.RestoreFlow();
            }
            _thread = null;
        }