How to use thread in Xamarin.Forms and How to Lock ?

For the UWP develop it can use 'Windows.System.Threading.ThreadPool.RunAsync' to create a thread, but it doesn't work on Xamarin.Forms.
I need a thread to do the network receive loop, so I also need the Lock, but I don't know how to use the Lock in Xamarin.Forms too.

I hope some one give me a demo code.