Sha256: 206e0a027e2cd0c74a3b07ca83be810b9dffe90851f6f0e5d5935664006c2dae
Contents?: true
Size: 1.98 KB
Versions: 41
Compression:
Stored size: 1.98 KB
Contents
require 'riak/client'
require 'riak/util/translation'
require 'thread'
module Riak
# 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.
class Stamp
attr_reader :client
CLIENT_ID_MASK = (1 << 10) - 1
SEQUENCE_MASK = (1 << 12) - 1
TIMESTAMP_MASK = (1 << 41) - 1
SEQUENCE_SHIFT = 10
TIMESTAMP_SHIFT = 22
# @param [Client] client a {Riak::Client} which will be used for
# the "worker ID" component of the stamp.
# @see Client#stamp
def initialize(client)
@client = client
@mutex = Mutex.new
@timestamp = time_gen
@sequence = 0
end
# Generates a k-sorted unique ID for use as a key or other
# disambiguation purposes.
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
private
def client_id
case id = @client.client_id
when Integer
id & CLIENT_ID_MASK
else
id.hash & CLIENT_ID_MASK
end
end
def time_gen
(Time.now.to_f * 1000).floor & TIMESTAMP_MASK
end
def wait_for_next_ms(start)
now = time_gen
now = time_gen while now <= start
now
end
end
# Raised when calling {Stamp#next} and NTP or some other external
# event has moved the system clock backwards.
class BackwardsClockError < StandardError
include Util::Translation
def initialize(delay)
super t('backwards_clock', :delay => delay)
end
end
end
Version data entries
41 entries across 31 versions & 4 rubygems