fiber_batch_loader.rb

fiber_test.rb

require "fiber"

# Set up a pretend database
DATA = {
  1 => "Hannah Coulter",
  2 => "Jayber Crow",
  3 => "That Distant Land"
}

# This loader will fetch items in batches of IDs
class Loader
  def initialize
    @ids = []
    @data = {}
  end

  def load(id)
    p "Adding #{id}"
    @ids << id
    Fiber.yield
    # Assumes that any batchable IDs will be added to this loader in the interim
    sync
    @data[id]
  end

  def sync
    if @ids.any?
      p "syncing #{@ids}"
      @ids.each { |id| @data[id] = DATA[id] }
      @ids = []
    end
  end
end

LOADER = Loader.new

def load_book(id:)
  # The important thing here is that the batch loading is completely hidden
  title = LOADER.load(id)
  title.upcase
end

# This is the pretend GraphQL-Ruby runtime: 

results = [nil, nil, nil]

# {path, fiber} tuples
fields = [
  [0, Fiber.new { load_book(id: 1) }],
  [1, Fiber.new { load_book(id: 2) }],
  [2, Fiber.new { load_book(id: 3) }],
]

while ((idx, f) = fields.shift) && (f.alive?)
  res = f.resume
  if f.alive?
    fields << [idx, f]
  else
    results[idx] = res
  end
end

pp results

# % ruby fiber_test.rb
# "Adding 1"
# "Adding 2"
# "Adding 3"
# "syncing [1, 2, 3]"
# ["HANNAH COULTER", "JAYBER CROW", "THAT DISTANT LAND"]