线程安全的 Rails 控制器操作 - 设置实例变量? [英] Thread-safe Rails controller actions - setting instance variables?

问题描述

我必须编写一个线程化的 Rails 应用程序，因为我在 Neo4j.rb 之上运行它，它在 Rails 进程中嵌入了一个 Neo4j 图形数据库，因此我必须为来自同一进程的多个请求提供服务.是的，如果连接到 Neo4j 数据库像 SQL 数据库一样工作会很酷，但事实并非如此，所以我不再抱怨，直接使用它.

I have to write a threaded Rails app because I am running it atop of Neo4j.rb, which embeds a Neo4j graph database inside the Rails process, and thus I have to serve multiple requests from the same process. Yeah, it'd be cool if connecting to a Neo4j database worked like SQL databases, but it doesn't, so I'll quit complaining and just use it.

我非常担心编写并发代码的影响(正如我应该的那样)，并且只需要一些关于如何处理常见场景的建议 - 控制器在会话哈希中设置实例变量或变量，然后会发生一些事情.考虑以下粗略的代码来演示我的意思:

I'm quite worried about the implications of writing concurrent code (as I should be), and just need some advice on how to handle common a common scenario - a controller sets an instance variable or a variable in the session hash, then some stuff happens. Consider the following crude code to demonstrate what I mean:

# THIS IS NOT REAL PRODUCTION CODE
# I don't do this in real life, it is just to help me ask my question, I
# know about one-way hashing, etc.!

class SessionsController
  def create
    user = User.find_by_email_and_password(params[:email], params[:password])
    raise 'auth error' unless user
    session[:current_user_id] = user.id
    redirect_to :controller => 'current_user', :action => 'show'
  end
end

class CurrentUserController
  def show
    @current_user = User.find(session[:current_user_id])
    render :action => :show # .html.erb file that uses @current_user
  end
end

问题:这段代码中是否存在竞争条件?

The question: Are there any race conditions in this code?

在 SessionsController 中，session 哈希和 params 哈希是线程本地的吗?假设同一个浏览器会话使用不同的凭据向/sessions#create(借用 Rails 路由语法)发出多个请求，登录的用户应该是命中该行的请求 session[:current_user_id] = user.id 最后?或者我应该在控制器动作周围包裹一个互斥锁?

In SessionsController, are the session hash and the params hash thread-local? Say the same browser session makes multiple requests to /sessions#create (to borrow Rails route syntax) with different credentials, the user that is logged in should be the request that hit the line session[:current_user_id] = user.id last? Or should I wrap a mutex lock around the controller action?

在 CurrentUserController 中，如果两个不同会话的请求同时触发 show 动作，是否会设置相同的 @current_user 变量?IE.第一个请求在处理 .html.erb 文件时会发现它的 @current_user 实例变量突然被第二个线程改变了吗?

In the CurrentUserController, if the show action is hit simultaneously by two requests with different sessions, will the same @current_user variable be set by both? I.e. will the first request, as it is processing the .html.erb file, find that it's @current_user instance variable has suddenly been changed by the second thread?

谢谢

推荐答案

每个请求都有一个 控制器的新实例.因此控制器实例变量是线程安全的.params 和 session 也由控制器实例变量(或请求对象本身)支持，因此也是安全的.

Each request gets a new instance of your controller. As a consequence controller instance variables are thread safe. params and session are also backed by controller instance variables (or the request object itself) and so are also safe.

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