Class: Continuity::RedisBackend

Inherits:
Object
  • Object
show all
Defined in:
lib/continuity/redis_backend.rb

Constant Summary collapse

LOCK_KEY = 
"continuity_lock"
LAST_SCHED_KEY = 
"continuity_scheduled_up_to"

Instance Method Summary collapse

Constructor Details

#initialize(redis, frequency = 10, lock_timeout = 30) ⇒ RedisBackend

Returns a new instance of RedisBackend.



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# File 'lib/continuity/redis_backend.rb', line 6

def initialize(redis, frequency = 10, lock_timeout = 30)
  @redis        = redis
  @lock_timeout = lock_timeout
  @frequency    = frequency
end

Instance Method Details

#lock_for_scheduling(now) ⇒ Object 



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# File 'lib/continuity/redis_backend.rb', line 12

def lock_for_scheduling(now)
  scheduled_up_to = @redis.get(LAST_SCHED_KEY).to_i

  # bootstrap
  if scheduled_up_to == 0
    lock(now) do

      # double check that someone else has bootstrapped
      # since we fetched the key
      scheduled_up_to = @redis.get(LAST_SCHED_KEY).to_i
      if scheduled_up_to == 0
        yield now - 1
        @redis.set(LAST_SCHED_KEY, now)

        return now
      else
        return scheduled_up_to
      end
    end

  end

  # this is tricky, we only want to attempt a lock
  # if there is a possibility we can schedule things.
  # BUT, once we attain a lock we need to make sure 
  # someone else hasn't already scheduled that period
  if (now - scheduled_up_to) >= @frequency
    lock(now) do
      scheduled_up_to = @redis.get(LAST_SCHED_KEY).to_i
      if (now - scheduled_up_to) >= @frequency
        # good we should still schedule
        yield scheduled_up_to
        @redis.set(LAST_SCHED_KEY, now)
        scheduled_up_to = now
      end
    end
  end

  scheduled_up_to
end