java: combined multithreaded / singlethreaded task queue

Question

I like the ExecutorService series of classes/interfaces. I don't have to worry about threads; I take in an ExecutorService instance and use it to schedule tasks, and if I want to use an 8-thread or 16-thread pool, well, great, I don't have to worry about that at all, it just happens depending on how the ExecutorService is setup. Hurray!

But what do I do if some of my tasks need to be executed in serial order? Ideally I would ask the ExecutorService to let me schedule these tasks on a single thread, but there doesn't seem to be any means of doing so.

edit: The tasks are not known ahead of time, they are an unlimited series of tasks that are erratically generated by events of various kinds (think random / unknown arrival process: e.g. clicks of a Geiger counter, or keystroke events).

Answer 1

You could write an implementation of Runnable that takes some tasks and executes them serially.

Something like:

public class SerialRunner implements Runnable {
    private List<Runnable> tasks;

    public SerialRunner(List<Runnable> tasks) {
        this.tasks = tasks;
    }

    public void run() {
        for (Runnable task: tasks) {
            task.run();
        }
    }
}