Module: Resque::Plugins::Locked

Included in:
RetryOnLock
Defined in:
lib/resque/plugins/locked.rb

Overview

If you want only one instance of your job running at a time, extend this module.

For example:

class UpdateNetworkGraph

extend Resque::Plugins::Locked
def self.perform(repo_id)
  heavy_lifting
end

end

While other UpdateNetworkGraph jobs will be placed on the queue, the Locked class will check Redis to see if any others are executing with the same arguments before beginning. If another is executing the job will be aborted.

If you want to define the key yourself you can override the ‘lock` class method in your subclass, e.g.

class UpdateNetworkGraph

extend Resque::Plugins::Locked
# Run only one at a time, regardless of repo_id.
def self.lock(repo_id)
  "network-graph"
end

def self.perform(repo_id)
  heavy_lifting
end

end

The above modification will ensure only one job of class UpdateNetworkGraph is running at a time, regardless of the repo_id. Normally a job is locked using a combination of its class name and arguments.

Instance Method Summary collapse

Instance Method Details

#around_perform_lock(*args) ⇒ Object

Locking algorithm: code.google.com/p/redis/wiki/SetnxCommand



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# File 'lib/resque/plugins/locked.rb', line 63

def around_perform_lock(*args)
  now = Time.now.to_i
  lock_key = "locked:#{lock(*args)}"
  lock_for = now + lock_time + 1
  lock_acquired = false
  # Acquire the lock.
  if Resque.redis.setnx(lock_key, lock_for)
    lock_acquired = true
  else
    # If we can't acquire the lock, see if it has expired.
    locked_until = Resque.redis.get(lock_key)
    if locked_until
      if locked_until.to_i < now
        locked_until = Resque.redis.getset(lock_key, lock_for)
        if locked_until.nil? or locked_until.to_i < now
          lock_acquired = true
        end
      end
    else
      lock_acquired = true
    end
  end
  if lock_acquired
    begin
      yield
    ensure
      Resque.redis.del(lock_key)
    end
  else
    on_lock(*args) if respond_to?(:on_lock)
  end
end

#lock(*args) ⇒ Object

Override in your subclass to control the lock key. It is passed the same arguments as ‘perform`, that is, your job’s payload.



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# File 'lib/resque/plugins/locked.rb', line 51

def lock(*args)
  "#{name}-#{args.to_s}"
end

#lock_time ⇒ Object

Override in your subclass to control how long the lock exists. Under normal circumstances, the lock will be removed when the job ends. If this doesn’t happen, the lock will be removed after this many seconds.



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# File 'lib/resque/plugins/locked.rb', line 58

def lock_time
  60
end

#locked?(*args) ⇒ Boolean

Convenience method to determine if a lock exists for this job, not used internally.

Returns:

  • (Boolean) 


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# File 'lib/resque/plugins/locked.rb', line 45

def locked?(*args)
  Resque.redis.exists "locked:#{lock(*args)}"
end