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

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]+)/
@@max_attempts = 
25
@@max_run_time = 
4.hours
@@worker_name =

Every worker has a unique name which by default is the pid of the process. There are some advantages to overriding this with something which survives worker retarts: Workers can safely resume working on tasks which are locked by themselves. The worker will assume that it crashed before.

nil

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 56

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 127

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).



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# File 'lib/delayed/job.rb', line 141

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)

  ActiveRecord::Base.silence do
    find(:all, :conditions => conditions, :order => NextTaskOrder, :limit => limit)
  end
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 168

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 215

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

.worker_name ⇒ Object 



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# File 'lib/delayed/job.rb', line 29

def self.worker_name
  return @@worker_name unless @@worker_name.nil?
  "host:#{Socket.gethostname} pid:#{Process.pid}" rescue "pid:#{Process.pid}"
end

.worker_name=(val) ⇒ Object 



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# File 'lib/delayed/job.rb', line 34

def self.worker_name=(val)
  @@worker_name = val
end

Instance Method Details

#failed? ⇒ Boolean Also known as: failed

Returns:

  • (Boolean) 


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# File 'lib/delayed/job.rb', line 60

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 234

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 182

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 < ?) and (run_at <= ?)", id, (now - max_run_time.to_i), now])
  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 208

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 69

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 65

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

#payload_object=(object) ⇒ Object 



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# File 'lib/delayed/job.rb', line 80

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 86

def reschedule(message, backtrace = [], time = nil)
  self.last_error   = message + "\n" + backtrace.join("\n")

  if (self.attempts += 1) < max_attempts
    time ||= Job.db_time_now + (attempts ** 4) + 5

    self.run_at       = time
    self.unlock
    save!
  else
    logger.info "* [JOB] PERMANENTLY removing #{self.name} because of #{attempts} consecutive failures."
    destroy_failed_jobs ? destroy : update_attribute(:failed_at, Delayed::Job.db_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 103

def run_with_lock(max_run_time, worker_name)
  logger.info "* [JOB] acquiring 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 acquire exclusive lock for #{name}"
    return nil # no work done
  end

  begin
    runtime =  Benchmark.realtime do
      Timeout.timeout(max_run_time.to_i) { invoke_job }
      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 202

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

#worker_name ⇒ Object 



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# File 'lib/delayed/job.rb', line 38

def worker_name
  self.class.worker_name
end

#worker_name=(val) ⇒ Object 



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# File 'lib/delayed/job.rb', line 42

def worker_name=(val)
  @@worker_name = val
end