Boxes (heap-allocates) the given value and returns an Arc to the object.
Boxes a closure and returns an Arc reference. Slower than just a box, but can derive traits like Clone.
Boxes a closure and returns a reference.
Boxes (heap-allocates) the given value and returns an Rc to the object.
Starts a new thread and runs the passed closure with the passed arguments in it, returning the new thread's hook.