Simplest way to run three methods in parallel in C#

Solution 1:

See the TPL documentation. They list this sample:

Parallel.Invoke(() => DoSomeWork(), () => DoSomeOtherWork());

So in your case this should just work:

Parallel.Invoke(
    () => results.LeftFront.CalcAi(),
    () => results.RightFront.CalcAi(),
    () => results.RearSuspension.CalcAi(geom, 
                                        vehDef.Geometry.LTa.TaStiffness, 
                                        vehDef.Geometry.RTa.TaStiffness));

EDIT: The call returns after all actions have finished executing. Invoke() is does not guarantee that they will indeed run in parallel, nor does it guarantee the order in which the actions execute.

Solution 2:

You can do this with tasks too (nicer if you later need Cancellation or something like results)

var task1 = Task.Factory.StartNew(() => results.LeftFront.CalcAi());
var task2 = Task.Factory.StartNew(() => results.RightFront.CalcAi());
var task3 = Task.Factory.StartNew(() =>results.RearSuspension.CalcAi(geom, 
                              vehDef.Geometry.LTa.TaStiffness, 
                              vehDef.Geometry.RTa.TaStiffness));

Task.WaitAll(task1, task2, task3);