Make Uuids have better random distribution

[dkropachev]

Before this commit Uuids used to initiate Random at point when it needs a random number.
Not only it is not efficient it also produced bad distribution which resulted in should_generate_unique_random_uuids_Random to fail, due to inability of Uuids::random generate unique vales.

I have tested it with:

  @Test
  public void should_generate_unique_random_uuids_Random() {
    for (int i = 0; i < 10000; i++) {
      System.out.println(i);
      Set<UUID> generated = serialGeneration(1_000_000, Uuids::random);
      assertThat(generated).hasSize(1_000_000);
    }
  }

Which was failing after 100 iterations before fix and never failed after.

[Bouncheck]

Instances of SplittableRandom are not thread-safe. They are designed to be split, not shared, across threads.

Docs do not reflect changes.

I think current master is good enough. I've seen this test fail only once so far in all those years.

[dkropachev]

Instances of SplittableRandom are not thread-safe. They are designed to be split, not shared, across threads.

Docs do not reflect changes.

I think current master is good enough. I've seen this test fail only once so far in all those years.

Thanks for pointing that out, I have moved it to use TrheadLocalRandom, please take a look