multithreading - C# Return value from function invoked in thread

Question

I have a calculating thread function which invokes message function from other thread using Invoke and I want that calculating thread to get value(of valuetype, like integer) from that message function. How can I do this?

The problem is that I still get old value of x variable after Invoke(...) and I expect value of 15

delegate void mes_del(object param);

void MyThreadFunc()
{
...
int x = 5;
object [] parms = new object []{x};
Invoke(new mes_del(MessageFunc), (object)parms);
...
}

void MessageFunc(object result)
{
   int res = 15;
   (result as object[])[0] = res;
}

I tried some approaches like using object[], object as parameters with no success. I though boxing/unboxing operations should occur in such a case but they don't. Should I use auxiliary type like it is done in .NET event mode and create mediator object like class holder { public int x; }

Answer 1

int x = 5;
object [] parms = new object []{x};

What the above code does is declare a local variable, assign it the value 5, then construct an object[] array containing one element which is a copy of that local variable.

You then pass this array into your Invoke call.

I think what you'll find is that after Invoke is called, parms[0] is 15. But this does not affect x, which would actually have to be passed as a ref parameter for any method to be able to modify its local value.

---

What I've seen done before is something like this:

class Box<T>
{
    public T Value { get; set; }
}

Then you could do:

void MyThreadFunc()
{
    var x = new Box<int> { Value = 5 };

    // By the way, there's really no reason to define your own
    // mes_del delegate type.
    Invoke(new Action<Box<int>>(MessageFunc), x);
}

void MessageFunc(Box<int> arg)
{
    arg.Value = 15;
}