Class: Delayed::Job

Inherits:
ActiveRecord::Base
  • Object
show all
Defined in:
lib/delayed/job.rb

Overview

A job object that is persisted to the database. Contains the work object as a YAML field.

Constant Summary collapse

MAX_ATTEMPTS = 
25
MAX_RUN_TIME = 
4.hours
NextTaskSQL = 
'(run_at <= ? AND (locked_at IS NULL OR locked_at < ?) OR (locked_by = ?)) AND failed_at IS NULL'
NextTaskOrder = 
'priority DESC, run_at ASC'
ParseObjectFromYaml = 
/\!ruby\/\w+\:([^\s]+)/

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.clear_locks! ⇒ Object

When a worker is exiting, make sure we don’t have any locked jobs.



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# File 'lib/delayed/job.rb', line 35

def self.clear_locks!
  update_all("locked_by = null, locked_at = null", ["locked_by = ?", worker_name])
end

.enqueue(*args, &block) ⇒ Object

Add a job to the queue



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# File 'lib/delayed/job.rb', line 106

def self.enqueue(*args, &block)
  object = block_given? ? EvaledJob.new(&block) : args.shift

  unless object.respond_to?(:perform) || block_given?
    raise ArgumentError, 'Cannot enqueue items which do not respond to perform'
  end

  priority = args.first || 0
  run_at   = args[1]

  Job.create(:payload_object => object, :priority => priority.to_i, :run_at => run_at)
end

.find_available(limit = 5, max_run_time = MAX_RUN_TIME) ⇒ Object

Find a few candidate jobs to run (in case some immediately get locked by others). Return in random order prevent everyone trying to do same head job at once.



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# File 'lib/delayed/job.rb', line 121

def self.find_available(limit = 5, max_run_time = MAX_RUN_TIME)

  time_now = db_time_now

  sql = NextTaskSQL.dup

  conditions = [time_now, time_now - max_run_time, worker_name]

  if self.min_priority
    sql << ' AND (priority >= ?)'
    conditions << min_priority
  end

  if self.max_priority
    sql << ' AND (priority <= ?)'
    conditions << max_priority
  end

  conditions.unshift(sql)

  records = ActiveRecord::Base.silence do
    find(:all, :conditions => conditions, :order => NextTaskOrder, :limit => limit)
  end

  records.sort_by { rand() }
end

.reserve_and_run_one_job(max_run_time = MAX_RUN_TIME) ⇒ Object

Run the next job we can get an exclusive lock on. If no jobs are left we return nil



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# File 'lib/delayed/job.rb', line 150

def self.reserve_and_run_one_job(max_run_time = MAX_RUN_TIME)

  # We get up to 5 jobs from the db. In case we cannot get exclusive access to a job we try the next.
  # this leads to a more even distribution of jobs across the worker processes
  find_available(5, max_run_time).each do |job|
    t = job.run_with_lock(max_run_time, worker_name)
    return t unless t == nil  # return if we did work (good or bad)
  end

  nil # we didn't do any work, all 5 were not lockable
end

.work_off(num = 100) ⇒ Object

Do num jobs and return stats on success/failure. Exit early if interrupted.



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# File 'lib/delayed/job.rb', line 197

def self.work_off(num = 100)
  success, failure = 0, 0

  num.times do
    case self.reserve_and_run_one_job
    when true
        success += 1
    when false
        failure += 1
    else
      break  # leave if no work could be done
    end
    break if $exit # leave if we're exiting
  end

  return [success, failure]
end

Instance Method Details

#failed? ⇒ Boolean Also known as: failed

Returns:

  • (Boolean) 


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# File 'lib/delayed/job.rb', line 39

def failed?
  failed_at
end

#invoke_job ⇒ Object

Moved into its own method so that new_relic can trace it.



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# File 'lib/delayed/job.rb', line 216

def invoke_job
  payload_object.perform
end

#lock_exclusively!(max_run_time, worker = worker_name) ⇒ Object

Lock this job for this worker. Returns true if we have the lock, false otherwise.



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# File 'lib/delayed/job.rb', line 164

def lock_exclusively!(max_run_time, worker = worker_name)
  now = self.class.db_time_now
  affected_rows = if locked_by != worker
    # We don't own this job so we will update the locked_by name and the locked_at
    self.class.update_all(["locked_at = ?, locked_by = ?", now, worker], ["id = ? and (locked_at is null or locked_at < ?)", id, (now - max_run_time.to_i)])
  else
    # We already own this job, this may happen if the job queue crashes.
    # Simply resume and update the locked_at
    self.class.update_all(["locked_at = ?", now], ["id = ? and locked_by = ?", id, worker])
  end
  if affected_rows == 1
    self.locked_at    = now
    self.locked_by    = worker
    return true
  else
    return false
  end
end

#log_exception(error) ⇒ Object

This is a good hook if you need to report job processing errors in additional or different ways



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# File 'lib/delayed/job.rb', line 190

def log_exception(error)
  logger.error "* [JOB] #{name} failed with #{error.class.name}: #{error.message} - #{attempts} failed attempts"
  logger.error(error)
end

#name ⇒ Object 



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# File 'lib/delayed/job.rb', line 48

def name
  @name ||= begin
    payload = payload_object
    if payload.respond_to?(:display_name)
      payload.display_name
    else
      payload.class.name
    end
  end
end

#payload_object ⇒ Object 



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# File 'lib/delayed/job.rb', line 44

def payload_object
  @payload_object ||= deserialize(self['handler'])
end

#payload_object=(object) ⇒ Object 



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# File 'lib/delayed/job.rb', line 59

def payload_object=(object)
  self['handler'] = object.to_yaml
end

#reschedule(message, backtrace = [], time = nil) ⇒ Object

Reschedule the job in the future (when a job fails). Uses an exponential scale depending on the number of failed attempts.



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# File 'lib/delayed/job.rb', line 65

def reschedule(message, backtrace = [], time = nil)
  if self.attempts < MAX_ATTEMPTS
    time ||= Job.db_time_now + (attempts ** 4) + 5

    self.attempts    += 1
    self.run_at       = time
    self.last_error   = message + "\n" + backtrace.join("\n")
    self.unlock
    save!
  else
    logger.info "* [JOB] PERMANENTLY removing #{self.name} because of #{attempts} consequetive failures."
    destroy_failed_jobs ? destroy : update_attribute(:failed_at, Time.now)
  end
end

#run_with_lock(max_run_time, worker_name) ⇒ Object

Try to run one job. Returns true/false (work done/work failed) or nil if job can’t be locked.



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# File 'lib/delayed/job.rb', line 82

def run_with_lock(max_run_time, worker_name)
  logger.info "* [JOB] aquiring lock on #{name}"
  unless lock_exclusively!(max_run_time, worker_name)
    # We did not get the lock, some other worker process must have
    logger.warn "* [JOB] failed to aquire exclusive lock for #{name}"
    return nil # no work done
  end

  begin
    runtime =  Benchmark.realtime do
      invoke_job # TODO: raise error if takes longer than max_run_time
      destroy
    end
    # TODO: warn if runtime > max_run_time ?
    logger.info "* [JOB] #{name} completed after %.4f" % runtime
    return true  # did work
  rescue Exception => e
    reschedule e.message, e.backtrace
    log_exception(e)
    return false  # work failed
  end
end

#unlock ⇒ Object

Unlock this job (note: not saved to DB)



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# File 'lib/delayed/job.rb', line 184

def unlock
  self.locked_at    = nil
  self.locked_by    = nil
end