Class: RedisLocks::Mutex

Inherits:
Object
  • Object
show all
Defined in:
lib/redis_locks/mutex.rb

Constant Summary collapse

NAMESPACE = 
"mutex"

Instance Method Summary collapse

Constructor Details

#initialize(key, expires_in: 86400, redis: RedisLocks.redis) ⇒ Mutex

Returns a new instance of Mutex.

Raises:

  • (ArgumentError) 


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# File 'lib/redis_locks/mutex.rb', line 18

def initialize(key, expires_in: 86400, redis: RedisLocks.redis)
  @key = "#{NAMESPACE}:#{key}"
  @redis = Connections.ensure_pool(redis)
  @expires_in = expires_in.to_i

  raise ArgumentError.new("Invalid expires_in: #{expires_in}") unless expires_in > 0
end

Instance Method Details

#expired?(safety_margin: 0) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/redis_locks/mutex.rb', line 75

def expired?(safety_margin: 0)
  return true unless @expires_at

  Time.now.utc.to_i + safety_margin >= @expires_at
end

#lock(expires_at: nil, &block) ⇒ Object 



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# File 'lib/redis_locks/mutex.rb', line 26

def lock(expires_at: nil, &block)
  now = Time.now.utc.to_i
  locked = false

  if expires_at
    expires_at = expires_at.to_i
  else
    expires_at = now + @expires_in
  end

  @redis.with do |conn|
    if conn.setnx(@key, expires_at)
      conn.expire(@key, expires_at - now)
      @expires_at = expires_at
      locked = true
    else # it was locked
      if (old_value = conn.get(@key)).to_i <= now
        # lock has expired
        if conn.getset(@key, expires_at) == old_value
          @expires_at = expires_at
          locked = true
        end
      end
    end
  end

  return false unless locked

  return_or_yield(&block)
end

#lock!(expires_at: nil, &block) ⇒ Object

Raises:



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# File 'lib/redis_locks/mutex.rb', line 57

def lock!(expires_at: nil, &block)
  locked = lock(expires_at: expires_at)
  raise AlreadyLocked.new(@key) unless locked
  return_or_yield(&block)
end

#not_expired!(safety_margin: 0) ⇒ Object

Raises:



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# File 'lib/redis_locks/mutex.rb', line 81

def not_expired!(safety_margin: 0)
  raise MutexExpired.new(@key) if expired?(safety_margin: safety_margin)
end

#unlock ⇒ Object 



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# File 'lib/redis_locks/mutex.rb', line 63

def unlock
  return unless @expires_at

  # To prevent deleting a lock acquired from another process, only delete
  # the key if it's still valid, and will be for another 2 seconds
  if !expired?(safety_margin: 2)
    @redis.with { |conn| conn.del(@key) }
  end

  @expires_at = nil
end