Module: Resque::Plugins::Lock

Defined in:
lib/resque/plugins/lock.rb

Overview

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

For example:

require ‘resque/plugins/lock’

class UpdateNetworkGraph

extend Resque::Plugins::Lock

def self.perform(repo_id)
  heavy_lifting
end

end

No other UpdateNetworkGraph jobs will be placed on the queue, the QueueLock class will check Redis to see if any others are queued with the same arguments before queueing. If another is queued the enqueue 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::Lock

# 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 



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# File 'lib/resque/plugins/lock.rb', line 78

def around_perform_lock(*args)
  begin
    yield
  ensure
    # Always clear the lock when we're done, even if there is an
    # error.
    Resque.redis.del(lock(*args))
  end
end

#before_enqueue_lock(*args) ⇒ Object

See the documentation for SETNX redis.io/commands/setnx for an explanation of this deadlock free locking pattern



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# File 'lib/resque/plugins/lock.rb', line 61

def before_enqueue_lock(*args)
  key = lock(*args)
  now = Time.now.to_i
  timeout = now + lock_timeout + 1

  # return true if we successfully acquired the lock
  return true if Resque.redis.setnx(key, timeout)

  # see if the existing timeout is still valid and return false if it is
  # (we cannot acquire the lock during the timeout period)
  return false if now <= Resque.redis.get(key).to_i

  # otherwise set the timeout and ensure that no other worker has
  # acquired the lock
  now > Resque.redis.getset(key, timeout).to_i
end

#lock(*args) ⇒ Object

Override in your job 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/lock.rb', line 55

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

#lock_timeout ⇒ Object

Override in your job to control the lock experiation time. This is the time in seconds that the lock should be considered valid. The default is one hour (3600 seconds).



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# File 'lib/resque/plugins/lock.rb', line 48

def lock_timeout
  3600
end