returning a variable from a worker thread

I have a worker thread, which returns a value (a System.Xml.XmlD ocument
object) to the main WinForm thread. I tried the below, but I'm not sure if
it's done correctly.

public class Form1: System.Windows. Forms.Form
{
// ...
System.Xml.XmlD ocument _xmldoc;
// ...
void Func1()
{
Thread workerthread = new Thread( new ThreadStart( Func2 ));
workerthread.St art();
}
void Func2()
{
SomeLib lib = new SomeLib(); // instantiate an object
_xmldoc = lib.LengthyOper ation(); // Can I assign a return value from a
thread operation to a private data member like this without any
synchronization ?
}