多线程并发Capybara请求？

Question

我的API允许用户购买某些独特的商品,其中每件商品只能出售给一个用户.因此,当多个用户尝试购买相同的项目时,一个用户应该得到响应:好的,另一个用户应该得到响应too_late.

现在,我的代码中似乎存在错误.竞争条件.如果两个用户试图在同一时间购买相同的项目,他们都得到了答案确定.这个问题在生产中显然是可重复的.现在我写了一个简单的测试,试图通过rspec重现它:

context "when I try to provoke a race condition" do
  # ...

  before do
    @concurrent_requests = 2.times.map do
      Thread.new do
        Thread.current[:answer] =  post "/api/v1/item/buy.json", :id => item.id
      end
    end

    @answers = @concurrent_requests.map do |th|
      th.join
      th[:answer].body
    end
  end

  it "should only sell the item to one user" do
    @answers.sort.should == ["ok", "too_late"].sort
  end
end

好像不会同时执行查询.为了测试这个,我将以下代码放入我的控制器操作中:

puts "Is it concurrent?"
sleep 0.2
puts "Oh Noez."

如果请求是并发的,则预期输出将是:

Is it concurrent?
Is it concurrent?
Oh Noez.
Oh Noez.

但是,我得到以下输出:

Is it concurrent?
Oh Noez.
Is it concurrent?
Oh Noez.

这告诉我,水豚的请求不会同时运行,而是一次运行一个.如何让我的capabara请求并发？

Answer 1

多线程和水豚不起作用,因为Capabara使用一个单独的服务器线程,它顺序处理连接.但如果你分叉,它就可以了.

我使用退出代码作为进程间通信机制.如果你做更复杂的东西,你可能想使用套接字.

这是我的快速和肮脏的黑客:

before do
  @concurrent_requests = 2.times.map do
    fork do
      # ActiveRecord explodes when you do not re-establish the sockets
      ActiveRecord::Base.connection.reconnect!

      answer = post "/api/v1/item/buy.json", :id => item.id

      # Calling exit! instead of exit so we do not invoke any rspec's `at_exit`
      # handlers, which cleans up, measures code coverage and make things explode.
      case JSON.parse(answer.body)["status"]
        when "accepted"
          exit! 128
        when "too_late"
          exit! 129
      end
    end
  end

  # Wait for the two requests to finish and get the exit codes.
  @exitcodes = @concurrent_requests.map do |pid|
    Process.waitpid(pid)
    $?.exitstatus
  end

  # Also reconnect in the main process, just in case things go wrong...
  ActiveRecord::Base.connection.reconnect!

  # And reload the item that has been modified by the seperate processs,
  # for use in later `it` blocks.
  item.reload
end

it "should only accept one of two concurrent requests" do
  @exitcodes.sort.should == [128, 129]
end

我使用相当奇特的退出代码,如128和129,因为如果未到达大小写块,进程将退出代码0,如果发生异常,则进程退出1.两者都不应该发生.因此,通过使用更高的代码,我会注意到出现问题.

Answer 2

您无法进行并发的水豚请求.但是,您可以创建多个capybara会话,并在同一测试中使用它们来模拟并发用户.

user_1 = Capybara::Session.new(:webkit) # or whatever driver
user_2 = Capybara::Session.new(:webkit)

user_1.visit 'some/page'
user_2.visit 'some/page'

# ... more tests ...

user_1.click_on 'Buy'
user_2.click_on 'Buy'