eventmachine和mysql2/em不回调

我希望以并发方式执行sql查询。因此，我在linux上的ruby 2.1.1上使用eventmachine和mysql2/em

但eventmachine不调用回调

当我的脚本运行时，这将被输出

"loop start"
"sql: select id from table where id = 1"
"loop end"
"loop start"
"sql: select id from table where id = 2"
"loop end"
"loop start"
"next loop"
"loop start"
"next loop"
.....

我想要这个输出

"loop start"
"sql: select id from table where id = 1"
"loop end"
"loop start"
"sql: select id from table where id = 2"
"loop end"
"loop start"
"next loop"
"callback"
"results"
"loop start"
"sql: select id from table where id = 3"
.....

怎么了

#!/usr/bin/env ruby

=begin
Gemfile

source 'https://rubygems.org'
gem 'eventmachine'
gem 'mysql2'
gem 'pry'
gem 'pry-debugger'
=end

require 'pp'
require 'bundler'
Bundler.require
require 'mysql2/em'

MYSQLINFO = {
  host: 'localhost',
  username: 'root',
  password: '',
  port: 3306,
}

SQLS = [
  'select id from table where id = 1',
  'select id from table where id = 2',
  'select id from table where id = 3',
  'select id from table where id = 4',
]
CONCURRENCY = 2

clients = []
CONCURRENCY.times do
  clients << Mysql2::EM::Client.new(MYSQLINFO)
end

EM.run do
  while true
    pp 'loop start'
    client = clients.shift

    if client.nil?
      # FIXME: I guess this point is wrong. Context must go to reactor thread?
      # but I don't know how to do.
      pp 'next loop'
      next
    end

    sql = SQLS.shift
    if sql.nil?
      break
    end

    defer = client.query(sql)

    pp "sql: #{sql}"

    defer.callback do |results|
      clients << client
      pp 'callback'
      pp results
    end
    pp 'loop end'
  end

  EM.stop
end

---

正如我在办公室里提到的，也许你不必在这里忙得团团转。 我认为每个客户机都应该在回调中调用下一个查询

Y = lambda do |f|
  lambda {|g| g[g]}[lambda do |g|
    f[lambda {|*args| g[g][*args]}]
    end]
end

EM.run do
  sql = 'select oppai from boins'

  clients.each do |client|
    Y[lambda {|f| lambda {|client, sql|
      client.query(sql).callback do |result|
        pp result.to_a.inspect
        f[client, sql]
      end
  }}][client, sql]
  end
end