Class: Riak::Stamp

Inherits:
Object show all
Defined in:
lib/riak/stamp.rb

Overview

Implements a client-side form of monotonically-increasing k-sorted unique identifiers. These are useful for key generation if your data is time-sequential and needs to be sorted by key, perhaps in Riak Search. Inspired by Twitter’s Snowflake project.

Constant Summary collapse

CLIENT_ID_MASK = 
(1 << 10) - 1
SEQUENCE_MASK = 
(1 << 12) - 1
TIMESTAMP_MASK = 
(1 << 41) - 1
SEQUENCE_SHIFT = 
10
TIMESTAMP_SHIFT = 
22

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(client) ⇒ Stamp

Returns a new instance of Stamp.

Parameters:

  • client (Client) —

    a Client which will be used for the “worker ID” component of the stamp.

See Also:



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# File 'lib/riak/stamp.rb', line 22

def initialize(client)
  @client = client
  @mutex = Mutex.new
  @timestamp = time_gen
  @sequence = 0
end

Instance Attribute Details

#client ⇒ Object (readonly)

Returns the value of attribute client.



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# File 'lib/riak/stamp.rb', line 11

def client
  @client
end

Instance Method Details

#next ⇒ Object

Generates a k-sorted unique ID for use as a key or other disambiguation purposes.



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# File 'lib/riak/stamp.rb', line 31

def next
  @mutex.synchronize do
    now = time_gen
    if @timestamp == now
      @sequence = (@sequence + 1) & SEQUENCE_MASK
      now = wait_for_next_ms(@timestamp) if @sequence == 0
    else
      @sequence = 0
    end

    raise BackwardsClockError.new(@timestamp - now) if now < @timestamp

    @timestamp = now
    @timestamp << TIMESTAMP_SHIFT | @sequence << SEQUENCE_SHIFT | client_id
  end
end