Class: Resque::Worker

Inherits:
Object
  • Object
show all
Extended by:
Helpers
Includes:
Helpers
Defined in:
lib/resque/worker.rb

Overview

A Resque Worker processes jobs. On platforms that support fork(2), the worker will fork off a child to process each job. This ensures a clean slate when beginning the next job and cuts down on gradual memory growth as well as low level failures.

It also ensures workers are always listening to signals from you, their master, and can react accordingly.

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Helpers

classify, constantize, decode, encode, redis

Constructor Details

#initialize(*queues) ⇒ Worker

Workers should be initialized with an array of string queue names. The order is important: a Worker will check the first queue given for a job. If none is found, it will check the second queue name given. If a job is found, it will be processed. Upon completion, the Worker will again check the first queue given, and so forth. In this way the queue list passed to a Worker on startup defines the priorities of queues.

If passed a single “*”, this Worker will operate on all queues in alphabetical order. Queues can be dynamically added or removed without needing to restart workers using this method.


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# File 'lib/resque/worker.rb', line 75

def initialize(*queues)
  @queues = queues
  validate_queues
end

Instance Attribute Details

#cant_forkObject

Boolean indicating whether this worker can or can not fork. Automatically set if a fork(2) fails.


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# File 'lib/resque/worker.rb', line 21

def cant_fork
  @cant_fork
end

#to_sObject Also known as: id

The string representation is the same as the id for this worker instance. Can be used with `Worker.find`.


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# File 'lib/resque/worker.rb', line 437

def to_s
  @to_s ||= "#{hostname}:#{Process.pid}:#{@queues.join(',')}"
end

#verboseObject

Whether the worker should log basic info to STDOUT


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# File 'lib/resque/worker.rb', line 14

def verbose
  @verbose
end

#very_verboseObject

Whether the worker should log lots of info to STDOUT


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# File 'lib/resque/worker.rb', line 17

def very_verbose
  @very_verbose
end

Class Method Details

.allObject

Returns an array of all worker objects.


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# File 'lib/resque/worker.rb', line 26

def self.all
  Array(redis.smembers(:workers)).map { |id| find(id) }
end

.attach(worker_id) ⇒ Object

Alias of `find`


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# File 'lib/resque/worker.rb', line 54

def self.attach(worker_id)
  find(worker_id)
end

.exists?(worker_id) ⇒ Boolean

Given a string worker id, return a boolean indicating whether the worker exists

Returns:

  • (Boolean)

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# File 'lib/resque/worker.rb', line 60

def self.exists?(worker_id)
  redis.sismember(:workers, worker_id)
end

.find(worker_id) ⇒ Object

Returns a single worker object. Accepts a string id.


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# File 'lib/resque/worker.rb', line 42

def self.find(worker_id)
  if exists? worker_id
    queues = worker_id.split(':')[-1].split(',')
    worker = new(*queues)
    worker.to_s = worker_id
    worker
  else
    nil
  end
end

.workingObject

Returns an array of all worker objects currently processing jobs.


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# File 'lib/resque/worker.rb', line 32

def self.working
  names = all
  return [] unless names.any?
  names.map! { |name| "worker:#{name}" }
  redis.mapped_mget(*names).keys.map do |key|
    find key.sub("worker:", '')
  end.compact
end

Instance Method Details

#==(other) ⇒ Object

Is this worker the same as another worker?


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# File 'lib/resque/worker.rb', line 427

def ==(other)
  to_s == other.to_s
end

#done_workingObject

Called when we are done working - clears our `working_on` state and tells Redis we processed a job.


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# File 'lib/resque/worker.rb', line 367

def done_working
  processed!
  redis.del("worker:#{self}")
end

#enable_gc_optimizationsObject

Enables GC Optimizations if you're running REE. www.rubyenterpriseedition.com/faq.html#adapt_apps_for_cow


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# File 'lib/resque/worker.rb', line 225

def enable_gc_optimizations
  if GC.respond_to?(:copy_on_write_friendly=)
    GC.copy_on_write_friendly = true
  end
end

#failedObject

How many failed jobs has this worker seen? Returns an int.


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# File 'lib/resque/worker.rb', line 384

def failed
  Stat["failed:#{self}"]
end

#failed!Object

Tells Redis we've failed a job.


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# File 'lib/resque/worker.rb', line 389

def failed!
  Stat << "failed"
  Stat << "failed:#{self}"
end

#forkObject

Not every platform supports fork. Here we do our magic to determine if yours does.


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# File 'lib/resque/worker.rb', line 192

def fork
  @cant_fork = true if $TESTING

  return if @cant_fork

  begin
    # IronRuby doesn't support `Kernel.fork` yet
    if Kernel.respond_to?(:fork)
      Kernel.fork
    else
      raise NotImplementedError
    end
  rescue NotImplementedError
    @cant_fork = true
    nil
  end
end

#hostnameObject

chomp'd hostname of this machine


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# File 'lib/resque/worker.rb', line 443

def hostname
  @hostname ||= `hostname`.chomp
end

#idle?Boolean

Boolean - true if idle, false if not

Returns:

  • (Boolean)

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# File 'lib/resque/worker.rb', line 416

def idle?
  state == :idle
end

#inspectObject


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# File 'lib/resque/worker.rb', line 431

def inspect
  "#<Worker #{to_s}>"
end

#jobObject Also known as: processing

Returns a hash explaining the Job we're currently processing, if any.


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# File 'lib/resque/worker.rb', line 405

def job
  decode(redis.get("worker:#{self}")) || {}
end

#kill_childObject

Kills the forked child immediately, without remorse. The job it is processing will not be completed.


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# File 'lib/resque/worker.rb', line 270

def kill_child
  if @child
    log! "Killing child at #{@child}"
    if system("ps -o pid,state -p #{@child}")
      Process.kill("KILL", @child) rescue nil
    else
      log! "Child #{@child} not found, restarting."
      shutdown
    end
  end
end

#log(message) ⇒ Object

Log a message to STDOUT if we are verbose or very_verbose.


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# File 'lib/resque/worker.rb', line 464

def log(message)
  if verbose
    puts "*** #{message}"
  elsif very_verbose
    time = Time.now.strftime('%I:%M:%S %Y-%m-%d')
    puts "** [#{time}] #$$: #{message}"
  end
end

#log!(message) ⇒ Object

Logs a very verbose message to STDOUT.


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# File 'lib/resque/worker.rb', line 474

def log!(message)
  log message if very_verbose
end

#pause_processingObject

Stop processing jobs after the current one has completed (if we're currently running one).


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# File 'lib/resque/worker.rb', line 284

def pause_processing
  log "USR2 received; pausing job processing"
  @paused = true
end

#perform(job) ⇒ Object

Processes a given job in the child.


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# File 'lib/resque/worker.rb', line 154

def perform(job)
  begin
    run_hook :after_fork, job
    job.perform
  rescue Object => e
    log "#{job.inspect} failed: #{e.inspect}"
    job.fail(e)
    failed!
  else
    log "done: #{job.inspect}"
  ensure
    yield job if block_given?
  end
end

#process(job = nil, &block) ⇒ Object

DEPRECATED. Processes a single job. If none is given, it will try to produce one. Usually run in the child.


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# File 'lib/resque/worker.rb', line 144

def process(job = nil, &block)
  return unless job ||= reserve

  working_on job
  perform(job, &block)
ensure
  done_working
end

#processedObject

How many jobs has this worker processed? Returns an int.


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# File 'lib/resque/worker.rb', line 373

def processed
  Stat["processed:#{self}"]
end

#processed!Object

Tell Redis we've processed a job.


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# File 'lib/resque/worker.rb', line 378

def processed!
  Stat << "processed"
  Stat << "processed:#{self}"
end

#procline(string) ⇒ Object

Given a string, sets the procline ($0) and logs. Procline is always in the format of:

resque-VERSION: STRING

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# File 'lib/resque/worker.rb', line 458

def procline(string)
  $0 = "resque-#{Resque::Version}: #{string}"
  log! $0
end

#prune_dead_workersObject

Looks for any workers which should be running on this server and, if they're not, removes them from Redis.

This is a form of garbage collection. If a server is killed by a hard shutdown, power failure, or something else beyond our control, the Resque workers will not die gracefully and therefore will leave stale state information in Redis.

By checking the current Redis state against the actual environment, we can determine if Redis is old and clean it up a bit.


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# File 'lib/resque/worker.rb', line 305

def prune_dead_workers
  all_workers = Worker.all
  known_workers = worker_pids unless all_workers.empty?
  all_workers.each do |worker|
    host, pid, queues = worker.id.split(':')
    next unless host == hostname
    next if known_workers.include?(pid)
    log! "Pruning dead worker: #{worker}"
    worker.unregister_worker
  end
end

#queuesObject

Returns a list of queues to use when searching for a job. A splat (“*”) means you want every queue (in alpha order) - this can be useful for dynamically adding new queues.


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# File 'lib/resque/worker.rb', line 186

def queues
  @queues[0] == "*" ? Resque.queues.sort : @queues
end

#register_signal_handlersObject

Registers the various signal handlers a worker responds to.

TERM: Shutdown immediately, stop processing jobs.

INT: Shutdown immediately, stop processing jobs.

QUIT: Shutdown after the current job has finished processing. USR1: Kill the forked child immediately, continue processing jobs. USR2: Don't process any new jobs CONT: Start processing jobs again after a USR2


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# File 'lib/resque/worker.rb', line 239

def register_signal_handlers
  trap('TERM') { shutdown!  }
  trap('INT')  { shutdown!  }

  begin
    trap('QUIT') { shutdown   }
    trap('USR1') { kill_child }
    trap('USR2') { pause_processing }
    trap('CONT') { unpause_processing }
  rescue ArgumentError
    warn "Signals QUIT, USR1, USR2, and/or CONT not supported."
  end

  log! "Registered signals"
end

#register_workerObject

Registers ourself as a worker. Useful when entering the worker lifecycle on startup.


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# File 'lib/resque/worker.rb', line 319

def register_worker
  redis.sadd(:workers, self)
  started!
end

#reserveObject

Attempts to grab a job off one of the provided queues. Returns nil if no job can be found.


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# File 'lib/resque/worker.rb', line 171

def reserve
  queues.each do |queue|
    log! "Checking #{queue}"
    if job = Resque::Job.reserve(queue)
      log! "Found job on #{queue}"
      return job
    end
  end

  nil
end

#run_hook(name, *args) ⇒ Object

Runs a named hook, passing along any arguments.


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# File 'lib/resque/worker.rb', line 325

def run_hook(name, *args)
  return unless hook = Resque.send(name)
  msg = "Running #{name} hook"
  msg << " with #{args.inspect}" if args.any?
  log msg

  args.any? ? hook.call(*args) : hook.call
end

#shutdownObject

Schedule this worker for shutdown. Will finish processing the current job.


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# File 'lib/resque/worker.rb', line 257

def shutdown
  log 'Exiting...'
  @shutdown = true
end

#shutdown!Object

Kill the child and shutdown immediately.


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# File 'lib/resque/worker.rb', line 263

def shutdown!
  shutdown
  kill_child
end

#startedObject

What time did this worker start? Returns an instance of `Time`


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# File 'lib/resque/worker.rb', line 395

def started
  redis.get "worker:#{self}:started"
end

#started!Object

Tell Redis we've started


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# File 'lib/resque/worker.rb', line 400

def started!
  redis.set("worker:#{self}:started", Time.now.to_s)
end

#startupObject

Runs all the methods needed when a worker begins its lifecycle.


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# File 'lib/resque/worker.rb', line 211

def startup
  enable_gc_optimizations
  register_signal_handlers
  prune_dead_workers
  run_hook :before_first_fork
  register_worker

  # Fix buffering so we can `rake resque:work > resque.log` and
  # get output from the child in there.
  $stdout.sync = true
end

#stateObject

Returns a symbol representing the current worker state, which can be either :working or :idle


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# File 'lib/resque/worker.rb', line 422

def state
  redis.exists("worker:#{self}") ? :working : :idle
end

#unpause_processingObject

Start processing jobs again after a pause


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# File 'lib/resque/worker.rb', line 290

def unpause_processing
  log "CONT received; resuming job processing"
  @paused = false
end

#unregister_workerObject

Unregisters ourself as a worker. Useful when shutting down.


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# File 'lib/resque/worker.rb', line 335

def unregister_worker
  # If we're still processing a job, make sure it gets logged as a
  # failure.
  if (hash = processing) && !hash.empty?
    job = Job.new(hash['queue'], hash['payload'])
    # Ensure the proper worker is attached to this job, even if
    # it's not the precise instance that died.
    job.worker = self
    job.fail(DirtyExit.new)
  end

  redis.srem(:workers, self)
  redis.del("worker:#{self}")
  redis.del("worker:#{self}:started")

  Stat.clear("processed:#{self}")
  Stat.clear("failed:#{self}")
end

#validate_queuesObject

A worker must be given a queue, otherwise it won't know what to do with itself.

You probably never need to call this.


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# File 'lib/resque/worker.rb', line 84

def validate_queues
  if @queues.nil? || @queues.empty?
    raise NoQueueError.new("Please give each worker at least one queue.")
  end
end

#work(interval = 5, &block) ⇒ Object

This is the main workhorse method. Called on a Worker instance, it begins the worker life cycle.

The following events occur during a worker's life cycle:

  1. Startup: Signals are registered, dead workers are pruned,

    and this worker is registered.
    
  2. Work loop: Jobs are pulled from a queue and processed.

  3. Teardown: This worker is unregistered.

Can be passed an integer representing the polling frequency. The default is 5 seconds, but for a semi-active site you may want to use a smaller value.

Also accepts a block which will be passed the job as soon as it has completed processing. Useful for testing.


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# File 'lib/resque/worker.rb', line 106

def work(interval = 5, &block)
  $0 = "resque: Starting"
  startup

  loop do
    break if @shutdown

    if not @paused and job = reserve
      log "got: #{job.inspect}"
      run_hook :before_fork
      working_on job

      if @child = fork
        rand # Reseeding
        procline "Forked #{@child} at #{Time.now.to_i}"
        Process.wait
      else
        procline "Processing #{job.queue} since #{Time.now.to_i}"
        perform(job, &block)
        exit! unless @cant_fork
      end

      done_working
      @child = nil
    else
      break if interval.to_i == 0
      log! "Sleeping for #{interval.to_i}"
      procline @paused ? "Paused" : "Waiting for #{@queues.join(',')}"
      sleep interval.to_i
    end
  end

ensure
  unregister_worker
end

#worker_pidsObject

Returns an array of string pids of all the other workers on this machine. Useful when pruning dead workers on startup.


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# File 'lib/resque/worker.rb', line 449

def worker_pids
  `ps -A -o pid,comm | grep [r]esque`.split("\n").map do |line|
    line.split(' ')[0]
  end
end

#working?Boolean

Boolean - true if working, false if not

Returns:

  • (Boolean)

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# File 'lib/resque/worker.rb', line 411

def working?
  state == :working
end

#working_on(job) ⇒ Object

Given a job, tells Redis we're working on it. Useful for seeing what workers are doing and when.


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# File 'lib/resque/worker.rb', line 356

def working_on(job)
  job.worker = self
  data = encode \
    :queue   => job.queue,
    :run_at  => Time.now.to_s,
    :payload => job.payload
  redis.set("worker:#{self}", data)
end