Class: Redis::Lock

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

Defined Under Namespace

Classes: ErrorBase, LostLock, Recovered, Script, Timeout

Constant Summary collapse

VERSION = 
'1.0.0'
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 



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# File 'lib/redis-lock.rb', line 35

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
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

.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 { |key| self.new(key, options) }
end

.key_group_key(options) ⇒ Object 



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# File 'lib/redis-lock.rb', line 25

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 173

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

#extend ⇒ Object

Raises:



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

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 59

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

#now ⇒ Object 



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# File 'lib/redis-lock.rb', line 169

def now
  Time.now
end

#synchronize(&block) ⇒ Object 



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# File 'lib/redis-lock.rb', line 49

def synchronize(&block)
  lock
  begin
    block.call
  ensure
    try_unlock
  end
rescue Recovered
end

#to_s ⇒ Object 



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# File 'lib/redis-lock.rb', line 177

def to_s
  @key
end

#try_extend ⇒ Object 



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# File 'lib/redis-lock.rb', line 150

def try_extend
  @@extend_script ||= Script.new "      local key = KEYS[1]\n      local key_group = KEYS[2]\n      local bare_key = ARGV[1]\n      local expires_at = tonumber(ARGV[2])\n      local token = ARGV[3]\n\n      if redis.call('hget', key, 'token') == token then\n        redis.call('hset', key, 'expires_at', expires_at)\n        redis.call('zadd', key_group, expires_at, bare_key)\n        return true\n      else\n        return false\n      end\n  LUA\n  !!@@extend_script.eval(@redis, :keys => [NAMESPACE + @key, @key_group_key], :argv => [@key, now.to_i + @expire, @token])\nend\n"

#try_lock(options = {}) ⇒ Object 



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# File 'lib/redis-lock.rb', line 72

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 "      local key = KEYS[1]\n      local key_group = KEYS[2]\n      local bare_key = ARGV[1]\n      local now = tonumber(ARGV[2])\n      local expires_at = tonumber(ARGV[3])\n      local recovery_data = ARGV[4]\n      local token_key = 'redis:lock:token'\n\n      local prev_expires_at = tonumber(redis.call('hget', key, 'expires_at'))\n      if prev_expires_at and prev_expires_at > now then\n        return {'locked', nil, nil}\n      end\n\n      local next_token = redis.call('incr', token_key)\n\n      redis.call('hset', key, 'expires_at', expires_at)\n      redis.call('hset', key, 'token', next_token)\n      redis.call('zadd', key_group, expires_at, bare_key)\n\n      if prev_expires_at then\n        return {'recovered', next_token, redis.call('hget', key, 'recovery_data')}\n      else\n        redis.call('hset', key, 'recovery_data', recovery_data)\n        return {'acquired', next_token, nil}\n      end\n  LUA\n  result, token, recovery_data = @@lock_script.eval(@redis,\n                                                    :keys => [NAMESPACE + @key, @key_group_key],\n                                                    :argv => [@key, now.to_i, now.to_i + @expire, options[:recovery_data]])\n\n  case result\n  when 'locked'\n    false\n  when 'acquired'\n    @token = token\n    true\n  when 'recovered'\n    @token = token\n    @recovery_data = recovery_data\n    :recovered\n  end\nend\n"

#try_unlock ⇒ Object 



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# File 'lib/redis-lock.rb', line 125

def try_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 "      local key = KEYS[1]\n      local key_group = KEYS[2]\n      local bare_key = ARGV[1]\n      local token = ARGV[2]\n\n      if redis.call('hget', key, 'token') == token then\n        redis.call('del', key)\n        redis.call('zrem', key_group, bare_key)\n        return true\n      else\n        return false\n      end\n  LUA\n  !!@@unlock_script.eval(@redis, :keys => [NAMESPACE + @key, @key_group_key], :argv => [@key, @token])\nend\n"

#unlock ⇒ Object

Raises:



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# File 'lib/redis-lock.rb', line 121

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