Like with running asadmin commands, there are two methods available for running
Callable objects, both also named run.
The two methods also work in a similar way to the two asadmin run methods:
run(Callable<T> callable)-
runs the specified Callable on all instances in a runtime’s cluster.
run(Collection<InstanceDescriptor>-
members, Callable<T> callable)` runs the Callable on a subset of the instances in a runtime’s cluster.
Both methods return a Map object with a key/value type of
<InstanceDescriptor, Future<T>>, where the type variable T is Serializable.