Class: Redis::Lock

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

Defined Under Namespace

Classes: Error, LostLock, NotLocked, Recovered, Script, Timeout

Constant Summary collapse

VERSION = 
'1.3.1'
NAMESPACE = 
'redis:lock'

Class Attribute Summary collapse

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(key, options = {}) ⇒ Lock

Returns a new instance of Lock.



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# File 'lib/redis-lock.rb', line 48

def initialize(key, options={})
  @options = options

  @key = key
  @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
  @token      = @options[:token]
end

Class Attribute Details

.expire ⇒ Object

Returns the value of attribute expire.



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

def expire
  @expire
end

.key_group ⇒ Object

Returns the value of attribute key_group.



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

def key_group
  @key_group
end

.redis ⇒ Object

Returns the value of attribute redis.



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

def redis
  @redis
end

.sleep ⇒ Object

Returns the value of attribute sleep.



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

def sleep
  @sleep
end

.timeout ⇒ Object

Returns the value of attribute timeout.



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

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 8

def key
  @key
end

#recovery_data ⇒ Object (readonly)

Returns the value of attribute recovery_data.



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# File 'lib/redis-lock.rb', line 9

def recovery_data
  @recovery_data
end

Class Method Details

.all(options = {}) ⇒ Object 



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# File 'lib/redis-lock.rb', line 28

def all(options={})
  redis = options[:redis] || self.redis
  raise "redis cannot be nil" if redis.nil?

  redis.zrangebyscore(key_group_key(options), 0, "+inf").to_a.map do |key_token|
    key, token = key_token.scan(/(.*):(.*)$/).first
    self.new(key, options.merge(:token => token))
  end
end

.expired(options = {}) ⇒ Object 



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

def expired(options={})
  redis = options[:redis] || self.redis
  raise "redis cannot be nil" if redis.nil?

  redis.zrangebyscore(key_group_key(options), 0, Time.now.to_i).to_a.map do |key_token|
    key, token = key_token.scan(/(.*):(.*)$/).first
    self.new(key, options.merge(:token => token))
  end
end

.key_group_key(options) ⇒ Object 



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# File 'lib/redis-lock.rb', line 38

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

Instance Method Details

#==(other) ⇒ Object 



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# File 'lib/redis-lock.rb', line 214

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

#extend ⇒ Object

Raises:



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# File 'lib/redis-lock.rb', line 171

def extend
  raise Redis::Lock::LostLock.new(self) unless try_extend
end

#lock(options = {}) ⇒ Object

Raises:



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# File 'lib/redis-lock.rb', line 76

def lock(options={})
  locked   = false
  start_at = now

  while now - start_at < @timeout
    break if locked = try_lock(options)
    sleep @sleep.to_f
  end

  raise Timeout.new(self)   unless locked
  raise Recovered.new(self) if locked == :recovered
end

#namespaced_key ⇒ Object 



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# File 'lib/redis-lock.rb', line 222

def namespaced_key
  NAMESPACE + ':' + @key
end

#now ⇒ Object 



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# File 'lib/redis-lock.rb', line 210

def now
  Time.now
end

#synchronize ⇒ Object 



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# File 'lib/redis-lock.rb', line 63

def synchronize
  begin
    lock
  rescue Recovered
  end

  begin
    yield
  ensure
    unlock
  end
end

#to_s ⇒ Object 



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# File 'lib/redis-lock.rb', line 218

def to_s
  @key
end

#try_extend ⇒ Object

Raises:



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# File 'lib/redis-lock.rb', line 175

def try_extend
  raise NotLocked.new('extend', self) unless @token

  @@extend_script ||= Script.new <<-LUA
      local key = KEYS[1]
      local key_group = KEYS[2]
      local bare_key = ARGV[1]
      local expires_at = tonumber(ARGV[2])
      local token = ARGV[3]
      local token_key = 'redis:lock:token'

      if redis.call('hget', key, 'token') == token then
        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('zrem', key_group, bare_key .. ':' .. token)
        redis.call('zadd', key_group, expires_at, bare_key .. ':' .. next_token)

        return { next_token, redis.call('hget', key, 'recovery_data') }
      else
        return false
      end
  LUA
  result = @@extend_script.eval(@redis, :keys => [namespaced_key, @key_group_key], :argv => [@key, now.to_i + @expire, @token])

  if result
    @token, @recovery_data = result
    true
  else
    false
  end
end

#try_lock(options = {}) ⇒ Object 



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# File 'lib/redis-lock.rb', line 89

def try_lock(options={})
  raise "recovery_data must be a string" if options[:recovery_data] && !options[:recovery_data].is_a?(String)

  # 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 bare_key = ARGV[1]
      local now = tonumber(ARGV[2])
      local expires_at = tonumber(ARGV[3])
      local recovery_data = ARGV[4]
      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, nil}
      end

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

      redis.call('hset', key, 'expires_at', expires_at)
      redis.call('zadd', key_group, expires_at, bare_key .. ':' .. next_token)

      local return_value = nil
      if prev_expires_at then
        redis.call('zrem', key_group, bare_key .. ':' .. redis.call('hget', key, 'token'))
        return_value =  {'recovered', next_token, redis.call('hget', key, 'recovery_data')}
      else
        redis.call('hset', key, 'recovery_data', recovery_data)
        return_value =  {'acquired', next_token, nil}
      end

      redis.call('hset', key, 'token', next_token)
      return return_value
  LUA
  result, token, recovery_data = @@lock_script.eval(@redis,
                                                    :keys => [namespaced_key, @key_group_key],
                                                    :argv => [@key, now.to_i, now.to_i + @expire, options[:recovery_data]])

  case result
  when 'locked'
    false
  when 'acquired'
    @token = token
    true
  when 'recovered'
    @token = token
    @recovery_data = recovery_data
    :recovered
  end
end

#try_unlock ⇒ Object

Raises:



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# File 'lib/redis-lock.rb', line 146

def try_unlock
  raise NotLocked.new('unlock', self) unless @token

  # 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 bare_key = ARGV[1]
      local token = ARGV[2]

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

#unlock ⇒ Object

Raises:



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# File 'lib/redis-lock.rb', line 142

def unlock
  raise Redis::Lock::LostLock.new(self) unless try_unlock
end