Class SnowflakeIdGenerator

  • All Implemented Interfaces:
    IdGenerator

    public final class SnowflakeIdGenerator
    extends AbstractSnowflakeIdGeneratorPaddingRhs
    implements IdGenerator
    Generate unique identifiers based on the Twitter Snowflake algorithm.

    This implementation is lock-less resulting in greater throughput plus less contention and latency jitter.

    Note: ntpd, or alternative clock source, should be setup correctly to ensure the clock does not go backwards.

    • Field Detail

      • UNUSED_BITS

        public static final int UNUSED_BITS
        High order 2's compliment bit which is unused.
        See Also:
        Constant Field Values
      • MAX_NODE_ID_AND_SEQUENCE_BITS

        public static final int MAX_NODE_ID_AND_SEQUENCE_BITS
        Total number of bits used to represent the distributed node and the sequence within a millisecond.
        See Also:
        Constant Field Values
      • NODE_ID_BITS_DEFAULT

        public static final int NODE_ID_BITS_DEFAULT
        Default number of bits used to represent the distributed node or application which is 10 bits allowing for 1024 nodes (0-1023).
        See Also:
        Constant Field Values
      • SEQUENCE_BITS_DEFAULT

        public static final int SEQUENCE_BITS_DEFAULT
        Default number of bits used to represent the sequence within a millisecond which is 12 bits supporting 4,096,000 ids per-second per-node.
        See Also:
        Constant Field Values
      • nodeIdAndSequenceBits

        private final int nodeIdAndSequenceBits
      • sequenceBits

        private final int sequenceBits
      • maxNodeId

        private final long maxNodeId
      • maxSequence

        private final long maxSequence
      • nodeBits

        private final long nodeBits
      • timestampOffsetMs

        private final long timestampOffsetMs
    • Constructor Detail

      • SnowflakeIdGenerator

        public SnowflakeIdGenerator​(int nodeIdBits,
                                    int sequenceBits,
                                    long nodeId,
                                    long timestampOffsetMs,
                                    EpochClock clock)
        Construct a new Snowflake id generator for a given node with a provided offset and EpochClock.
        Parameters:
        nodeIdBits - number of bits used to represent the distributed node or application.
        sequenceBits - number of bits used to represent the sequence within a millisecond.
        nodeId - for the node generating ids.
        timestampOffsetMs - to adjust the base offset from 1 Jan 1970 UTC to extend the 69-year range.
        clock - to provide timestamps.
    • Method Detail

      • nodeId

        public long nodeId()
        Node identity which scopes the id generation. This is limited to maxNodeId().
        Returns:
        the node identity which scopes the id generation.
      • timestampOffsetMs

        public long timestampOffsetMs()
        Offset in milliseconds from Epoch of 1 Jan 1970 UTC which is subtracted to give 69 years of ids.

        To offset from 1 Jan 2015 UTC then 1420070400000 can be used.

        Returns:
        offset in milliseconds from Epoch of 1 Jan 1970 UTC which is subtracted to give 69 years of ids.
      • maxNodeId

        public long maxNodeId()
        The max node identity value possible given the configured number of node ID bits.
        Returns:
        max node identity value.
      • maxSequence

        public long maxSequence()
        The max sequence value possible given the configured number of sequence bits.
        Returns:
        max sequence value.
      • nextId

        public long nextId()
        Generate the next id in sequence. If maxSequence() is reached within the same millisecond then this implementation will busy spin until the next millisecond using Thread.onSpinWait() and checking for Thread.isInterrupted().
        Specified by:
        nextId in interface IdGenerator
        Returns:
        the next unique id for this node.
      • extractTimestamp

        long extractTimestamp​(long id)
      • extractNodeId

        long extractNodeId​(long id)
      • extractSequence

        long extractSequence​(long id)