C# Error: Cannot use ref or out parameter 'stringval' inside an anonymous method, lambda expression, or query expression

Hi

i want to pass parameter in a function using ref  ,  

but this function needs to be called from thread...

when i try to build using ref as parameter,it says

Cannot use ref or out parameter 'stringval' inside an anonymous method, lambda expression, or query expression

how to pass it as ref , or any alternative