minimal example

delegate void asyncPayload();

async void callAsync(asyncPayload func)
{
    SourceFunc callback = callAsync.callback;
    ThreadFunc<void*> run = () => {
        func();
        Idle.add((owned) callback);
        return null;
    };

    new GLib.Thread<void*>("callAsync", run);
    yield;
}

void testFunc(int arg1, string arg2)
{
    stdout.printf("arg1: %i\n", arg1);
    stdout.printf("arg2: %s\n", arg2);
}

void main()
{
    int testInt = 5;
    string testString = "test-string";

    asyncPayload pl = () => {
        testFunc(testInt, testString);
    };
    callAsync.begin(pl, (obj, res) => { callAsync.end(res); });

    var loop = new MainLoop(null, false);
    loop.run();
}