Class: CloudCrowd::WorkUnit

Inherits:
ActiveRecord::Base
  • Object
show all
Includes:
ModelStatus
Defined in:
lib/cloud_crowd/models/work_unit.rb

Overview

A WorkUnit is an atomic chunk of work from a job, processing a single input through a single action. The WorkUnits are run in parallel, with each worker daemon processing one at a time. The splitting and merging stages of a job are each run as a single WorkUnit.

Class Method Summary collapse

Instance Method Summary collapse

Methods included from ModelStatus

#complete?, #display_status, #failed?, included, #incomplete?, #merging?, #processing?, #splitting?, #succeeded?

Class Method Details

.cancel_all_reservations ⇒ Object

Cancels all outstanding WorkUnit reservations for all processes. (Useful in the console for debugging.)



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# File 'lib/cloud_crowd/models/work_unit.rb', line 56

def self.cancel_all_reservations
  WorkUnit.update_all('reservation = null')
end

.cancel_reservations ⇒ Object

Cancels all outstanding WorkUnit reservations for this process.



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# File 'lib/cloud_crowd/models/work_unit.rb', line 50

def self.cancel_reservations
  WorkUnit.reserved.update_all('reservation = null')
end

.distribute_to_nodes ⇒ Object

Attempt to send a list of work_units to nodes with available capacity. A single central server process stops the same WorkUnit from being distributed to multiple nodes by reserving it first. The algorithm used should be lock-free.



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# File 'lib/cloud_crowd/models/work_unit.rb', line 24

def self.distribute_to_nodes
  return unless WorkUnit.reserve_available
  work_units = WorkUnit.reserved
  available_nodes = NodeRecord.available
  until work_units.empty? do
    node = available_nodes.shift
    unit = work_units.first
    break unless node && unit
    next unless node.actions.include? unit.action
    sent = node.send_work_unit(unit)
    if sent
      work_units.shift
      available_nodes.push(node) unless node.busy?
    end
  end
ensure
  WorkUnit.cancel_reservations
end

.find_by_worker_name(name) ⇒ Object

Look up a WorkUnit by the worker that’s currently processing it. Specified by pid@host.



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# File 'lib/cloud_crowd/models/work_unit.rb', line 62

def self.find_by_worker_name(name)
  pid, host = name.split('@')
  node = NodeRecord.find_by_host(host)
  node && node.work_units.find_by_worker_pid(pid)
end

.reserve_available ⇒ Object

Reserves all available WorkUnits for this process. Returns false if there were none available.



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# File 'lib/cloud_crowd/models/work_unit.rb', line 45

def self.reserve_available
  WorkUnit.available.update_all("reservation = #{$$}") > 0
end

.start(job, action, input, status) ⇒ Object

Convenience method for starting a new WorkUnit.



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# File 'lib/cloud_crowd/models/work_unit.rb', line 69

def self.start(job, action, input, status)
  self.create(:job => job, :action => action, :input => input, :status => status)
end

Instance Method Details

#assign_to(node_record, worker_pid) ⇒ Object

When a Node checks out a WorkUnit, establish the connection between WorkUnit and NodeRecord and record the worker_pid.



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# File 'lib/cloud_crowd/models/work_unit.rb', line 123

def assign_to(node_record, worker_pid)
  update_attributes!(:node_record => node_record, :worker_pid => worker_pid)
end

#fail(output, time_taken) ⇒ Object

Mark this unit as having failed. May attempt a retry.



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# File 'lib/cloud_crowd/models/work_unit.rb', line 98

def fail(output, time_taken)
  tries = self.attempts + 1
  return try_again if tries < CloudCrowd.config[:work_unit_retries]
  update_attributes({
    :status         => FAILED,
    :node_record    => nil,
    :worker_pid     => nil,
    :attempts       => tries,
    :output         => output,
    :time           => time_taken
  })
  self.job.check_for_completion
end

#finish(result, time_taken) ⇒ Object

Mark this unit as having finished successfully. Splitting work units are handled differently (an optimization) – they immediately fire off all of their resulting WorkUnits for processing, without waiting for the rest of their splitting cousins to complete.



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# File 'lib/cloud_crowd/models/work_unit.rb', line 77

def finish(result, time_taken)
  if splitting?
    [JSON.parse(parsed_output(result))].flatten.each do |new_input|
      WorkUnit.start(job, action, new_input, PROCESSING)
    end
    self.destroy
    job.set_next_status if job && job.done_splitting?
  else
    update_attributes({
      :status         => SUCCEEDED,
      :node_record    => nil,
      :worker_pid     => nil,
      :attempts       => attempts + 1,
      :output         => result,
      :time           => time_taken
    })
    job && job.check_for_completion
  end
end

#parsed_output(out = self.output) ⇒ Object

All output needs to be wrapped in a JSON object for consistency (unfortunately, JSON.parse needs the top-level to be an object or array). Convenience method to provide the parsed version.



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# File 'lib/cloud_crowd/models/work_unit.rb', line 130

def parsed_output(out = self.output)
  JSON.parse(out)['output']
end

#to_json ⇒ Object

The JSON representation of a WorkUnit shares the Job’s options with all its cousin WorkUnits.



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# File 'lib/cloud_crowd/models/work_unit.rb', line 136

def to_json
  {
    'id'        => self.id,
    'job_id'    => self.job_id,
    'input'     => self.input,
    'attempts'  => self.attempts,
    'action'    => self.action,
    'options'   => JSON.parse(self.job.options),
    'status'    => self.status
  }.to_json
end

#try_again ⇒ Object

Ever tried. Ever failed. No matter. Try again. Fail again. Fail better.



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# File 'lib/cloud_crowd/models/work_unit.rb', line 113

def try_again
  update_attributes({
    :node_record  => nil,
    :worker_pid   => nil,
    :attempts     => self.attempts + 1
  })
end