Class: Redis::Lock

Inherits:
Object
  • Object
show all
Defined in:
lib/robust-redis-lock/version.rb,
lib/redis-lock.rb

Defined Under Namespace

Classes: Script

Constant Summary collapse

VERSION = 
'0.4.1'

Class Attribute Summary collapse

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(*args) ⇒ Lock

Returns a new instance of Lock.



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# File 'lib/redis-lock.rb', line 39

def initialize(*args)
  raise "invalid number of args: expected 1..3, got #{args.length}" if args.length < 1 || args.length > 3

  key = args.shift
  raise "key cannot be nil" if key.nil?

  if args.length == 2
    @data = args.shift
  end

  @options = args.shift || {}

  namespace_prefix = self.class.namespace_prefix(@options) unless key.start_with?(self.class.namespace_prefix(@options))
  @key = [namespace_prefix, key].compact.join(':')
  @key_group_key = self.class.key_group_key(@options)

  @redis    = @options[:redis] || self.class.redis
  raise "redis cannot be nil" if @redis.nil?

  @timeout    = @options[:timeout]    || self.class.timeout
  @expire     = @options[:expire]     || self.class.expire
  @sleep      = @options[:sleep]      || self.class.sleep
  @serializer = @options[:serializer] || self.class.serializer
end

Class Attribute Details

.expire ⇒ Object

Returns the value of attribute expire.



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# File 'lib/redis-lock.rb', line 13

def expire
  @expire
end

.key_group ⇒ Object

Returns the value of attribute key_group.



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# File 'lib/redis-lock.rb', line 15

def key_group
  @key_group
end

.namespace ⇒ Object

Returns the value of attribute namespace.



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# File 'lib/redis-lock.rb', line 14

def namespace
  @namespace
end

.redis ⇒ Object

Returns the value of attribute redis.



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# File 'lib/redis-lock.rb', line 10

def redis
  @redis
end

.serializer ⇒ Object

Returns the value of attribute serializer.



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# File 'lib/redis-lock.rb', line 16

def serializer
  @serializer
end

.sleep ⇒ Object

Returns the value of attribute sleep.



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# File 'lib/redis-lock.rb', line 12

def sleep
  @sleep
end

.timeout ⇒ Object

Returns the value of attribute timeout.



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# File 'lib/redis-lock.rb', line 11

def timeout
  @timeout
end

Instance Attribute Details

#key ⇒ Object (readonly)

Returns the value of attribute key.



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# File 'lib/redis-lock.rb', line 7

def key
  @key
end

Class Method Details

.expired(options = {}) ⇒ Object 



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# File 'lib/redis-lock.rb', line 18

def expired(options={})
  redis = options[:redis] || self.redis
  redis.zrangebyscore(key_group_key(options), 0, Time.now.to_i).to_a.map { |key| self.new(key, options) }
end

.key_group_key(options) ⇒ Object 



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# File 'lib/redis-lock.rb', line 23

def key_group_key(options)
  [namespace_prefix(options), (options[:key_group] || self.key_group), 'group'].join(':')
end

.namespace_prefix(options) ⇒ Object 



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# File 'lib/redis-lock.rb', line 27

def namespace_prefix(options)
  (options[:namespace] || self.namespace)
end

Instance Method Details

#==(other) ⇒ Object 



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# File 'lib/redis-lock.rb', line 166

def ==(other)
  self.key == other.key
end

#data ⇒ Object 



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# File 'lib/redis-lock.rb', line 79

def data
  @data ||= @serializer.load(@redis.hget(key, 'data'))
end

#extend ⇒ Object 



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# File 'lib/redis-lock.rb', line 144

def extend
  @@extend_script ||= Script.new <<-LUA
      local key = KEYS[1]
      local key_group = KEYS[2]
      local expires_at = tonumber(ARGV[1])
      local token = ARGV[2]

      if redis.call('hget', key, 'token') == token then
        redis.call('hset', key, 'expires_at', expires_at)
        redis.call('zadd', key_group, expires_at, key)
        return true
      else
        return false
      end
  LUA
  !!@@extend_script.eval(@redis, :keys => [@key, @key_group_key], :argv => [now.to_i + @expire, @token])
end

#lock ⇒ Object 



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# File 'lib/redis-lock.rb', line 64

def lock
  result = false
  start_at = now
  while now - start_at < @timeout
    break if result = try_lock
    sleep @sleep.to_f
  end

  yield if block_given? && result

  result
ensure
  unlock if block_given?
end

#now ⇒ Object 



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# File 'lib/redis-lock.rb', line 162

def now
  Time.now
end

#try_lock ⇒ Object 



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# File 'lib/redis-lock.rb', line 83

def try_lock
  # This script loading is not thread safe (touching a class variable), but
  # that's okay, because the race is harmless.
  @@lock_script ||= Script.new <<-LUA
      local key = KEYS[1]
      local key_group = KEYS[2]
      local now = tonumber(ARGV[1])
      local expires_at = tonumber(ARGV[2])
      local data = ARGV[3]
      local token_key = 'redis:lock:token'

      local prev_expires_at = tonumber(redis.call('hget', key, 'expires_at'))
      if prev_expires_at and prev_expires_at > now then
        return {'locked', nil}
      end

      local next_token = redis.call('incr', token_key)

      redis.call('hset', key, 'expires_at', expires_at)
      redis.call('hset', key, 'token', next_token)
      redis.call('hset', key, 'data', data)
      redis.call('zadd', key_group, expires_at, key)

      if prev_expires_at then
        return {'recovered', next_token}
      else
        return {'acquired', next_token}
      end
  LUA
  result, token = @@lock_script.eval(@redis, :keys => [@key, @key_group_key], :argv => [now.to_i, now.to_i + @expire, @serializer.dump(@data)])

  @token = token if token

  case result
  when 'locked'    then return false
  when 'recovered' then return :recovered
  when 'acquired'  then return true
  end
end

#unlock ⇒ Object 



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# File 'lib/redis-lock.rb', line 123

def unlock
  # Since it's possible that the operations in the critical section took a long time,
  # we can't just simply release the lock. The unlock method checks if @expire_at
  # remains the same, and do not release when the lock timestamp was overwritten.
  @@unlock_script ||= Script.new <<-LUA
      local key = KEYS[1]
      local key_group = KEYS[2]
      local token = ARGV[1]

      if redis.call('hget', key, 'token') == token then
        redis.call('del', key)
        redis.call('zrem', key_group, key)
        return true
      else
        return false
      end
  LUA
  result = @@unlock_script.eval(@redis, :keys => [@key, @key_group_key], :argv => [@token])
  !!result
end