Use atomic timestamp for sensitive tests.

[enozcan]

As discussed in #126, millisecond resolution may fall short when updates are frequent. This behavior can be tolerable in deployments since the cache will restore itself after a cache miss. However in test environment this makes some tests inconsistent. This will not be the case anymore when the new factory is used.

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[pivovarit]

Looks good. However, we should revisit the idea of using SimpleTimestamper.next() instead of our home-grown Clock.currentTimeMillis() in production for the local region cache.

This is what was here before recent changes.

SimpleTimestamper was introduced at some point as a part of Hibernate SPI:

/**
 * Generates increasing identifiers (in a single VM only). Not valid across multiple VMs.  Identifiers are not
 * necessarily strictly increasing, but usually are.
 * <p/>
 * Core while loop implemented by Alex Snaps - EHCache project - under ASL 2.0
 *
 * @author Hibernate team
 * @author Alex Snaps
 */
public final class SimpleTimestamper {
    private static final int BIN_DIGITS = 12;
    private static final AtomicLong VALUE = new AtomicLong();

    public static final short ONE_MS = 1 << BIN_DIGITS;

    public static long next() {
        while (true) {
            long base = System.currentTimeMillis() << BIN_DIGITS;
            long maxValue = base + ONE_MS - 1;

            for (long current = VALUE.get(), update = Math.max(base, current + 1); update < maxValue;
                 current = VALUE.get(), update = Math.max(base, current + 1)) {
                if (VALUE.compareAndSet(current, update)) {
                    return update;
                }
            }
        }
    }
    // ...
}

[pivovarit]

For the curious ones out there. A simple "benchmark " showing how drastic the difference can be:

        System.out.println(Stream.generate(() -> System.currentTimeMillis())
          .limit(1000)
          .distinct()
          .count()); // 3

        System.out.println(Stream.generate(() -> Clock.currentTimeMillis())
          .limit(1000)
          .distinct()
          .count()); // 4

        System.out.println(Stream.generate(() -> SimpleTimestamper.next())
          .limit(1000)
          .distinct()
          .count()); // 1000