Class: BackgroundJobQueue

Inherits:
Object
  • Object
show all
Defined in:
backend/app/lib/background_job_queue.rb

Constant Summary collapse

JOB_TIMEOUT_SECONDS = 
AppConfig[:job_timeout_seconds].to_i

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.init ⇒ Object 



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# File 'backend/app/lib/background_job_queue.rb', line 186

def self.init
  # cancel jobs left in a running state from a previous run
  begin
    Job.running_jobs_untouched_since(Time.now - JOB_TIMEOUT_SECONDS).each do |job|
      job.finish!(:canceled)
    end
  rescue => e
    Log.error("Error trying to cancel old jobs: #{e.class} #{$!} #{$@}")
  end


  queue = BackgroundJobQueue.new
  queue.start_background_threads
end

Instance Method Details

#get_next_job ⇒ Object 



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# File 'backend/app/lib/background_job_queue.rb', line 26

def get_next_job
  # First cancel any jobs that are in a running state but which haven't
  # been touched by their watchdog for a time greater than the configured timeout.
  # This shouldn't really happen, but his replaces the concept of a stale job
  # used in an earlier implementation that was problematic because it could end up
  # calling the #run method on a job more than once.
  begin
    Job.running_jobs_untouched_since(Time.now - JOB_TIMEOUT_SECONDS).each do |job|
      job.finish!(:canceled)
    end
  rescue Sequel::NoExistingObject
    Log.debug("Another thread cancelled unwatched job #{job.id}, nothing to do on #{Thread.current[:name]}")
  rescue => e
    Log.error("Error trying to cancel unwatched jobs on #{Thread.current[:name]}: #{e.class} #{$!} #{$@}")
  end

  DB.open do |db|
    Job.queued_jobs.each do |job|
      runner = JobRunner.registered_runner_for(job.type)

      begin
        unless runner
          Log.error("No runner registered for #{job.type} job #{job.id}! " +
                    "Marking as canceled on #{Thread.current[:name]}")

          job.finish!(:canceled)
          next
        end

        if !runner.run_concurrently && Job.any_running?(job.type)
          Log.debug("Job type #{job.type} is not registered to run concurrently " +
                    "and there's currently one running, so skipping job #{job.id} " +
                    "on #{Thread.current[:name]}")
          next
        end

        # start the job here to prevent other threads from grabbing it
        job.start!

        return job

      rescue Sequel::NoExistingObject
        # Another thread handled this job.
        Log.info("Another thread is handling job #{job.id}, skipping on #{Thread.current[:name]}")
      end
    end
  end
  # No jobs to run at this time
  false
end

#run_pending_job ⇒ Object 



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# File 'backend/app/lib/background_job_queue.rb', line 78

def run_pending_job
  job = get_next_job

  return if !job

  finished = Atomic.new(false)
  job_canceled = Atomic.new(false)
  job_thread_name = Thread.current[:name]

  watchdog_thread = Thread.new do
    while !finished.value
      DB.open do |db|
        Log.debug("Running job #{job.id} on #{job_thread_name}")
        job = job.class.any_repo[job.id]

        if job.status === "canceled"
          # Notify the running job that we've been manually canceled
          Log.info("Received cancel request for job #{job.id} on #{job_thread_name}")
          job_canceled.value = true
        end

        job.update_mtime
      end

      sleep [5, (JOB_TIMEOUT_SECONDS / 2)].min
    end
  end

  begin
    runner = JobRunner.for(job)

    # Give the runner a ref to the canceled atomic,
    # so it can find out if it's been canceled
    runner.cancelation_signaler(job_canceled)

    runner.add_success_hook do
      # Upon success, have the job set our status to "completed" at the right
      # point.  This allows the batch import to set the job status within the
      # same DB transaction that handled the import (avoiding a situation
      # where the import completes and commits, but the job status update
      # fails separately)
      #
      finished.value = true
      watchdog_thread.join

      job.finish!(:completed)
    end

    runner.run

    finished.value = true
    watchdog_thread.join

    if job_canceled.value
      # Mark the job as permanently canceled
      job.finish!(:canceled)
    else
      if job.running?
        # If the job didn't record success, mark it as finished ourselves.
        # This isn't really a problem, but it does mean that the job status
        # update is now happening in a separate DB transaction than the one
        # that ran the job.  If the system crashed after the job finished but
        # prior to this point, the job might have finished successfully
        # without being recorded as such.
        #
        Log.warn("Job #{job.id} finished successfully but didn't report success.  " +
                 "Marking it as finished successfully ourselves, on #{job_thread_name}.")
        runner.success!
      end
    end
  rescue => e
    Log.error("Job #{job.id} on #{job_thread_name} failed: #{e.class} #{$!} #{$@}")
    # If anything went wrong, make sure the watchdog thread still stops.
    finished.value = true
    watchdog_thread.join

    unless job.success?
      job.finish!(:failed)
    end
  end

  Log.debug("Completed job #{job.id} on #{job_thread_name}")
end

#start_background_thread(thread_number) ⇒ Object 



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# File 'backend/app/lib/background_job_queue.rb', line 163

def start_background_thread(thread_number)
  Thread.new do
    Thread.current[:name] = "background job thread #{thread_number} (#{Thread.current.object_id})"
    Log.info("Starting #{Thread.current[:name]}")
    while true
      begin
        run_pending_job
      rescue => e
        Log.error("Error in #{Thread.current[:name]}: #{e.class} #{$!} #{$@}")
      end
      sleep AppConfig[:job_poll_seconds].to_i
    end
  end
end

#start_background_threads ⇒ Object 



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# File 'backend/app/lib/background_job_queue.rb', line 179

def start_background_threads
  AppConfig[:job_thread_count].to_i.times do |i|
    start_background_thread(i+1)
  end
end