Your question details are ambiguous - your example suggests that two threads can be handed the same Pair
but you say otherwise in the description.
As the more difficult to achieve, I will offer an Iterable<Pair<Q,E>>
that will deliver Pair
s one per thread until the supplier cycles - then it will repeat.
public interface Supplier<T> {
public int size();
public T get(int index);
}
public interface PairSupplier<Q, E> extends Supplier<Pair<Q, E>> {
}
public class IterableSupplier<T> implements Iterable<T> {
// The common supplier to use across all threads.
final Supplier<T> supplier;
// The atomic counter.
final AtomicInteger i = new AtomicInteger();
public IterableSupplier(Supplier<T> supplier) {
this.supplier = supplier;
}
@Override
public Iterator<T> iterator() {
/**
* You may create a NEW iterator for each thread while they all share supplier
* and Will therefore distribute each Pair between different threads.
*
* You may also share the same iterator across multiple threads.
*
* No two threads will get the same pair twice unless the sequence cycles.
*/
return new ThreadSafeIterator();
}
private class ThreadSafeIterator implements Iterator<T> {
@Override
public boolean hasNext() {
/**
* Always true.
*/
return true;
}
private int pickNext() {
// Just grab one atomically.
int pick = i.incrementAndGet();
// Reset to zero if it has exceeded - but no spin, let "just someone" manage it.
int actual = pick % supplier.size();
if (pick != actual) {
// So long as someone has a success before we overflow int we're good.
i.compareAndSet(pick, actual);
}
return actual;
}
@Override
public T next() {
return supplier.get(pickNext());
}
@Override
public void remove() {
throw new UnsupportedOperationException("Remove not supported.");
}
}
}
NB: I have adjusted the code a little to accommodate both scenarios. You can take an Iterator
per thread or share a single Iterator
across threads.