How to find out if all executorservice threads have finished

Hi,
There is a function process which does the following
        for(i = 0;i<100;i++){
        executorservice.submit(task);
        }
       once all the threads have finished there tasks i want to update a table.. How do i know if all the threads have finished the tasks...As the process function will comeout once the threads have finished the task. so probably i need to put a listener somewhere.

Thanks

Thanks