Javascript / Coffeescript background task / job / thread - single and multiple array batch iteration with cancellation using background.js (https://github.com/kmalakoff/background)

gistfile1.coffee

Using background.js (https://github.com/kmalakoff/background)...

    constructor: ->
      @processing_count = 0
      @transformations_job_queue = new BGJobQueue(100)

    _transformationsChangeCallback: ->
      # reset the job queue to start again rather than waiting for the last batch to complete
      @processing_count++; @_updateProcessingMesage()
      @transformations_job_queue.clear()

      # break up the processing work into batches of 50 combinations between models and transformations
      if(@transformations.length)
        @transformations_job_queue.push(
          (=> iterator = new BGArrayIterator_xN([@collection.models, @transformations], 50)), 
          (-> return iterator.nextByItems((items) ->
            model = items[0]; transformation = items[1]
            model.applyTransformation(transformation)
          ))
        )

      # update view's knowledge of visibilities in batches of 100
      @transformations_job_queue.push(
        (=> iterator = new BGArrayIterator(@collection.models, 100)), 
        (=> return iterator.nextByRange((range) =>
          show_models = []
          hide_models = []
          while(not range.isDone())
            model = @collection.models[range.index]
            if(model.isVisible())
              show_models.push(model.id)
            else
              hide_models.push(model.id)
            range.step()
        
          @batchShowByModelIds(show_models) if show_models.length
          @batchHideByModelIds(hide_models) if hide_models.length
        )),
        ((was_cancelled) =>
          @processing_count--; @_updateProcessingMesage()
          return if was_cancelled 
          view.animatedZoomToModel(@collection.models[0]) if @collection.models.length
        )
      )