初探 ActiveJob

简介

ActiveJob 是 Rails 4.2 新加入的功能。这个东西在 beta 阶段 rubyChina 就已经有很多高手关注了，无奈自己的项目使用的是 4.1.5，升级到 4.2 的时候其他 gem 又有很多依赖有问题，所以没在第一时间使用。今天补个课。

ActiveJob 是 Rails 自己开发运行后台程序的模块，常用于执行运行时间可能很长的工作（比如发送注册邮件）。

当然这种需求实际上非常普遍，所以 rails 也有相应的第三方 gem 来解决这个需求，比如著名的 Sidekiq 和 Resque 等。ActiveJob 的出现不是为了代替他们，而是统一了原来 Resque、Sidekiq 等其他 gem 对后台运行程序的各种千奇百怪的写法。

定义

ActiveJob 的使用官方文档已经给出了示例 首先在命令行中使用 rails g job JOBNAME 来新建一个任务

比如这里

➜  my_rails42 git:(master) ✗ rails g job add_lots_of_users
      invoke  test_unit
      create    test/jobs/add_lots_of_users_job_test.rb
      create  app/jobs/add_lots_of_users_job.rb
➜  my_rails42 git:(master) ✗

我们打开 add_lots_of_users_job.rb，可以看到下列内容

class AddLotsOfUsersJob < ActiveJob::Base
  queue_as :default

  def perform(*args)
    # Do something later
  end
end

我们可以将耗时的内容写入perform里

def perform(*args)
  # Do something later
  sleep 10
  1000.times do |index|
    user = User.new
    user.name = "atpking#{index}"
    user.save
  end
end

我们可以看到，我在 job 里建立了一个作业，先睡 10 秒，再插入 1000 条数据到数据库中

至此，我们就成功建立了一个 job 了，接下来，就是使用了

使用

官方 demo 讲的非常简单，就是在你使用的地方用这个句子：XXJob.perform_later PARAMS

比如我这里

class UsersController < ApplicationController
  before_action :set_user, only: [:show, :edit, :update, :destroy]

  # GET /users
  # GET /users.json
  def index
    AddLotsOfUsersJob.perform_later
    @users = User.all
  end
end

我们运行一下试试

运行过程中发现不像我们预想的那样，而是访问 index 的时候，活生生的等待了 10 多秒，在获得@users

[ActiveJob] [AddLotsOfUsersJob] [e191c62d-68a9-425f-8a94-b9fe080c141c]    (0.8ms)  commit transaction
[ActiveJob] [AddLotsOfUsersJob] [e191c62d-68a9-425f-8a94-b9fe080c141c]    (0.0ms)  begin transaction
[ActiveJob] [AddLotsOfUsersJob] [e191c62d-68a9-425f-8a94-b9fe080c141c]   SQL (0.2ms)  INSERT INTO "users" ("name", "created_at", "updated_at") VALUES (?, ?, ?)  [["name", "atpking999"], ["created_at", "2015-04-20 04:30:29.320703"], ["updated_at", "2015-04-20 04:30:29.320703"]]
[ActiveJob] [AddLotsOfUsersJob] [e191c62d-68a9-425f-8a94-b9fe080c141c]    (0.6ms)  commit transaction
[ActiveJob] [AddLotsOfUsersJob] [e191c62d-68a9-425f-8a94-b9fe080c141c] Performed AddLotsOfUsersJob from Inline(default) in 12789.38ms
  User Load (2.1ms)  SELECT "users".* FROM "users"
  Rendered users/index.html.erb within layouts/application (186.7ms)
Completed 200 OK in 13210ms (Views: 392.6ms | ActiveRecord: 1166.0ms)

注意看上面，很多歌 ActiveJob 完毕了之后，输出Performed AddLotsOfUsersJob from Inline(default) in 12789.38ms,再执行的select * from users

也就是说，默认情况下的 ActiveJob 跟我们使用的方法没什么区别，是阻塞的，实际上官方文档也说明了

4 Job Execution If no adapter is set, the job is immediately executedIf no adapter is set, the job is immediately executed.

那么我们需要给 ActiveJob 指定一个 Adapter 了。官方有支持以下的 adapter，功能有所不同，需要注意。如果没设定，则是默认的 Active Job Inline，可以看到一个悲剧，不支持异步（Async），这也是为何我们刚刚等了很长时间

function	Async	Queues	Delayed	Priorities	Timeout	Retries
Backburner	Yes	Yes	Yes	Yes	Job	Global
Delayed Job	Yes	Yes	Yes	Job	Global	Global
Qu	Yes	Yes	No	No	No	Global
Que	Yes	Yes	Yes	Job	No	Job
queue_classic	Yes	Yes	No*	No	No	No
Resque	Yes	Yes	Yes (Gem)	Queue	Global	Yes
Sidekiq	Yes	Yes	Yes	Queue	No	Job
Sneakers	Yes	Yes	No	Queue	Queue	No
Sucker Punch	Yes	Yes	No	No	No	No
Active Job Inline(默认的)	No	Yes	N/A	N/A	N/A	N/A
Active Job	Yes	Yes	Yes	No	No	No

我选用了 sidekiq 作为 Adapter，注意这里，你必须要安装过 sidekiq, 没安装自然需要你 Gemfile 里加一句咯 同时还要安装 redis，之后在命令行使用 redis-server & 启用 redis 同时也得在命令行里启用 sidekiq，直接输入 sidekiq & 即可

之后我们需要指定 sidekiq 为我们的 adapter，我们需要在 application.rb 里加入一句话

config.active_job.queue_adapter = :sidekiq

再次运行 index 页面，我们看 rails 的日志，就变成了先执行 Select * from Users，返回页面结果，再继续执行 jobs 的内容了。

Started GET "/users" for ::1 at 2015-04-20 12:16:20 +0800
Processing by UsersController#index as HTML
[ActiveJob] Enqueued AddLotsOfUsersJob (Job ID: 50372234-6cf7-4ad2-b886-fd3029f4ea3d) to Sidekiq(default)
2015-04-20T04:16:20Z 79432 TID-ouzlum9ig ActiveJob::QueueAdapters::SidekiqAdapter::JobWrapper JID-eb96be6e314f6926583a1267 INFO: start
  User Load (0.3ms)  SELECT "users".* FROM "users"
  Rendered users/index.html.erb within layouts/application (4.1ms)
Completed 200 OK in 72ms (Views: 57.8ms | ActiveRecord: 0.5ms)


Started GET "/assets/jquery_ujs.self-8e98a7a072a6cee1372d19fff9ff3e6aa1e39a37d89d6f06861637d061113ee7.js?body=1" for ::1 at 2015-04-20 12:16:21 +0800


Started GET "/assets/users.self-e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855.css?body=1" for ::1 at 2015-04-20 12:16:21 +0800


Started GET "/assets/jquery.self-d03a5518f45df77341bdbe6201ba3bfa547ebba8ed64f0ea56bfa5f96ea7c074.js?body=1" for ::1 at 2015-04-20 12:16:21 +0800


Started GET "/assets/application.self-e80e8f2318043e8af94dddc2adad5a4f09739a8ebb323b3ab31cd71d45fd9113.css?body=1" for ::1 at 2015-04-20 12:16:21 +0800


Started GET "/assets/scaffolds.self-a98ac27100e3e5ca7065dbd7c898e5afa02690ec2ef84ccc02f65c4c20057b83.css?body=1" for ::1 at 2015-04-20 12:16:21 +0800


Started GET "/assets/turbolinks.self-c37727e9bd6b2735da5c311aa83fead54ed0be6cc8bd9a65309e9c5abe2cbfff.js?body=1" for ::1 at 2015-04-20 12:16:21 +0800


Started GET "/assets/users.self-877aef30ae1b040ab8a3aba4e3e309a11d7f2612f44dde450b5c157aa5f95c05.js?body=1" for ::1 at 2015-04-20 12:16:21 +0800


Started GET "/assets/application.self-3a3c8b61bda630ee689740ce7cbd0dd8ea6fdd45e2c42eef4661ab38cf268afe.js?body=1" for ::1 at 2015-04-20 12:16:21 +0800
2015-04-20T04:16:33Z 79432 TID-ouzlum9ig ActiveJob::QueueAdapters::SidekiqAdapter::JobWrapper JID-eb96be6e314f6926583a1267 INFO: done: 12.828 sec

请注意上面的这两句话

2015-04-20T04:16:20Z 79432 TID-ouzlum9ig ActiveJob::QueueAdapters::SidekiqAdapter::JobWrapper JID-eb96be6e314f6926583a1267 INFO: start

2015-04-20T04:16:33Z 79432 TID-ouzlum9ig ActiveJob::QueueAdapters::SidekiqAdapter::JobWrapper JID-eb96be6e314f6926583a1267 INFO: done: 12.828 sec