Multithreading: invokeAll runs a batch and waits for every result

ExecutorService.invokeAll submits a whole collection of tasks and blocks until all of them complete, returning their Futures in the same order the tasks were given. That fixed ordering is what makes the collected results deterministic.

Code

ExecutorService pool = Executors.newFixedThreadPool(2);
List<Callable<Integer>> tasks = List.of(() -> 2 * 2, () -> 3 * 3, () -> 4 * 4);
List<Future<Integer>> futures = pool.invokeAll(tasks);
List<Integer> results = new ArrayList<>();
for (Future<Integer> f : futures) results.add(f.get());
pool.shutdown();
System.out.println("Results in submission order: " + results);

Output

Results in submission order: [4, 9, 16]