Java 8 Streams - Timeout?

Question

I want to loop over a huge array and do a complicated set of instructions that takes a long time. However, if more than 30 seconds have passed, I want it to give up.

ex.

final long start = System.currentTimeMillis();
myDataStructure.stream()
    .while(() -> System.currentTimeMillis() <= start + 30000)
    .forEach(e ->
    {
      ...
    });

I want to avoid just saying return inside the forEach call if a certain condition is met.

Answer 1

I would create a custom pool for that, something like:

ForkJoinPool forkJoinPool = new ForkJoinPool(1);
    try {
        forkJoinPool.submit(() ->
        IntStream.range(1, 1_000_000).filter(x -> x > 2).boxed().collect(Collectors.toList()))
                .get(30, TimeUnit.MILLISECONDS);
    } catch (TimeoutException e) {
        // job not done in your interval
    }

Answer 2

If iterating the stream or array in this case is cheap compared to actually executing the operation than just use a predicate and filter whether time is over or not.

final long end = System.nanoTime() + TimeUnit.SECONDS.toNanos(30L);
myDataStructure.stream()
    .filter(e -> System.nanoTime() <= end)
    .forEach(e ->
    {
      ...
    });

Question is if you need to know which elements have been processed or not. With the above you have to inspect whether a side effect took place for a specific element afterwards.