Question

I work on a simulation system, where at each timestep, I have to simulate many models. I used a FixedThreadPool to speed up the calculation:

ExecutorService executor = Executors.newFixedThreadPool(nThread);
for (Model m : models) {
  executor.execute( m.simulationTask() );
}
executor.shutdown();
while ( ! executor.awaitTermination(10, TimeUnit.MINUTES) ) { 
  System.out.println("wait"); 
}

Now, the executor can’t be used to execute() new Tasks after calling shutdown(). Is there a way to reset the executor, so I can reuse the existing executor (and its threads) at the next simulation step?

Answer 1

You can reuse the executor service if you restructure your code somewhat.

Collection<Callable<Integer>> tasks = new ArrayList<Callable<Integer>>(16);
for (Model m : models) {
  tasks.add(m.simulationTask());
}

ExecutorService executor = Executors.newFixedThreadPool(nThread);
try {
  executor.invokeAll(tasks);
} catch(InterruptedException ie) {
  // Handle this
}

Basically you collect all your tasks, execute them, and await execution before proceeding. Of course, you could also alternatively just use a new Executor Service for each of your time steps, but at least you have options.

Caveats: I didn’t compile the code so there might be errors. I also assumed an Integer parameter type for convenience.