sqs.rb

class SQS
  attr_reader :aws, :queue_url
  def initialize(aws)
    @aws = aws
    @queue_url = "https://sqs.us-east-1.amazonaws.com/my-topic-for-sqs"
  end

  def publish_msg(msg)
    aws.send_message(queue_url: queue_url, message_body: JSON.generate(msg))
  end
end

sqs = SQS.new(Aws::SQS::Client.new)

# users is just an array of hashes
users.each do |user|
  # i'd like this to be async
  sqs.publish_msg(user)
end

# I don't want the program to end until all threads have finished

Take a look at this: https://gist.github.com/jdantonio/c4b77b1f724c0aad2b50