A Java implementation similar to Twitter's now deprecated Snowflake ID that is thread-safe. Note that this is only the library for generating the ids. It does not include a service that provides ids to calling backend services.

Note: This project does not include a backend service for id generation.

// Default generator
SnowflakeGenerator generator = SnowflakeGenerator.getDefault();

// Generator with custom configurations
SnowflakeGenerator generator = SnowflakeConfiguration.builder()
      .withTimestampBits(41)
      .withDatacenterBits(8)
      .withWorkerBits(2)
      .withSequenceBits(12)
      .build(),
    GeneratorConfiguration.builder()
      .withDataCenter(1L)
      .withWorker(6L)
      .withOverflowStrategy(OverflowStrategy.SPIN_WAIT)
      .build(),
    new DefaultTime(Clock.systemDefaultZone(), Instant.now()));

Java 9 or above is required.

<dependency>
  <groupId>io.github.spiderpig86</groupId>
  <artifactId>jayflake</artifactId>
  <version>0.1</version>
</dependency>

implementation 'io.github.spiderpig86:jayflake:0.1'

Below is a diagram depicting the structure of a default Snowflake id.

• The first bit is unused to make ordering easier across both signed and unsigned values.
• The next 41 bits are the timestamp, or the number of ticks since the epoch. By default, this can store a range of 69 years from the epoch where the tick duration is 1 millisecond.
• The next 4 bits store an id indicating the data center of which the machine lives in.
• The next 6 bits store an id of the worker generating the id.
• The last 12 bits store a count representing the sequence to handle any collisions.

+------------+---------------------+-----------+---------+----------------------+
| 1 Bit      | 41 Bit              | 4 Bit     | 6 Bit   | 12 Bit               |
| Unused     | Timestamp           | Data Ctr  | Worker  | Sequence Number      |
+------------+---------------------+-----------+---------+----------------------+

Based on the example above which shows id 21941452820491 in binary, we know the following:

• 5231250 ticks passed since the epoch.
• The data center is 0.
• The worker is 5.
• The sequence id is 11.

One of the strengths of this implementation is that you are not tied down to the default configuration. There are 3 main types of classes that determine the generator's behavior.

The structure of the Snowflake id's bits is controlled by the SnowflakeConfiguration, a centralized place that determines which bits are reserved for what functionality.

For example, if you think the data center bits are unnecessary and want to copy the original Snowflake id's format of a 41 bit timestamp, 10 bit worker id, and 12 bit sequence id, you can do the following:

SnowflakeGenerator generator =
    SnowflakeGenerator.create(
        SnowflakeConfiguration.builder()
        .withTimestampBits(41)
        .withDatacenterBits(0)
        .withWorkerBits(10)
        .withSequenceBits(12)
        .build(),
    GeneratorConfiguration.builder()
        .withDataCenter(0L)
        .withWorker(5L)
        .withOverflowStrategy(OverflowStrategy.SLEEP_WITH_JITTER)
        .build(),
    DefaultTime.getDefault(c));

The GeneratorConfiguration houses all the settings used while generating the ids themselves, such as the data center, worker id, and overflow strategy.

GeneratorConfiguration.builder()
    .withDataCenter(0L)
    .withWorker(5L)
    .withOverflowStrategy(OverflowStrategy.SLEEP_WITH_JITTER)
    .build()

These classes are the source of truth of the epoch (similar to the UNIX epoch) and the length of each tick. The DefaultTime class is provided out of the box which uses a tick duration of 1ms.

You can increase the duration of the tick to whatever duration you want to extend how much time the id can span. Keep in mind that this can increase the number of ids that are generated with the same timestamp which runs the risk of overflowing the sequence bits.

Below is an example Time class which uses 1s as the tick duration.

public class OneSecondTime extends Time {

  private final long tickDurationMs;

  public OneSecondTime(@Nonnull final Clock clock, @Nonnull final Instant epoch) {
    super(clock, epoch);
    this.tickDurationMs = 1000L;
  }

  @Override
  public long getTickDurationMs() {
    return tickDurationMs;
  }
}

Snowflake ids are no strangers to overflow situations, especially if the bits are configured improperly. Even if they are, with high enough QPS, we may run out of numbers. In the event this happens, you can set a specific OverflowStrategy for when values overflow.

• SLEEP - SnowflakeGenerator will sleep for a provided duration in milliseconds.
• SLEEP_WITH_JITTER - SnowflakeGenerator will sleep for a provided duration plus a random jitter in milliseconds.
• SPIN_WAIT - SnowflakeGenerator will provide a system hint to allow other threads to be scheduled and while two provided values are equal.
• THROW_EXCEPTION - SnowflakeGenerator will throw an exception when encountering an overflow.

Currently, this applies to the sequence bits. If the timestamp overflows, you have a much bigger problem on your hands.

This project is licensed under the MIT license. Please see the license for more details.