bare-bones example with concurrent-ruby gem of async io with limiting in flight requests to an arbitrary size

async-throttle.rb

#!/usr/bin/env ruby

require 'json'
require 'date'
require 'http'
require 'concurrent'

# I could not get bundle to install the 'concurrent-edge' gem so I just
# grabbed a couple classes I needed. code for Concurrent::Throttle is here:
# https://github.com/ruby-concurrency/concurrent-ruby/blob/master/lib-edge/concurrent/edge/throttle.rb
#
# Throttle lso uses Concurrent::LockFreeQueue, which is here:
# https://github.com/ruby-concurrency/concurrent-ruby/blob/master/lib-edge/concurrent/edge/lock_free_queue.rb
require './lib/throttle' 

START           = Time.now.utc
N_ITER          = 100
MAX_CONCURRENCY = 10
N_EXECUTING     = Concurrent::AtomicFixnum.new 0
N_STARTED       = Concurrent::AtomicFixnum.new 0
THROTTLE        = Concurrent::Throttle.new MAX_CONCURRENCY

def http_request(n)
  resp = HTTP.get('http://worldclockapi.com/api/json/utc/now')
  raise StandardError if resp.code != 200
  d = JSON.load(resp.body)
  utc = d['currentDateTime']
  puts "#{Time.now.utc - START} #{utc} #{n}" # #{resp.body}"
  utc
end

# technique used adapted from Throttle docs example: http://ruby-concurrency.github.io/concurrent-ruby/master/Concurrent/Throttle.html
# in original example, it loads value from N_EXECUTING to demonstrate the number of
# jobs in flight does not exceed the throttle limit
job = -> do
  N_EXECUTING.increment
  n = N_STARTED.increment(1)
  utc = http_request(n)
  N_EXECUTING.decrement
  utc
end 

request_results = Array.new(N_ITER) do  
  Thread.new do
    THROTTLE.acquire(&job)   
  end
end.map(&:value)

puts "#{request_results}"