Rails.cache在不同的线程中不能缓存? [英] Rails.cache in different threads not caching?

问题描述

Rails项目中的缓存方法结果有问题.

I have a problem with caching method results in rails project.

我来到了这段代码，它模拟了两个不同的请求:

I came to this code that simulates two different requests:

[  
   Thread.new { puts Rails.cache.fetch('a', expires_in: 2.seconds) { rand } }, 
   Thread.new { puts Rails.cache.fetch('a', expires_in: 2.seconds) { rand } } 
]

尝试在Rails控制台中执行它. 如果尝试在控制台中将其作为输出运行，则会得到不同的数字.那怎么可能?

Try to execute it in a rails console. If I try to run it in a console as output I get different numbers. How is that possible?

但是例如，此代码(带有睡眠)可以按预期工作:

But for example this code (with sleep) works as intended:

[  
  Thread.new { sleep(1); puts Rails.cache.fetch('a', expires_in: 2.seconds) { rand } }, 
  Thread.new { puts Rails.cache.fetch('a', expires_in: 2.seconds) { rand } } 
]

推荐答案

在第一个代码块中

[  
  Thread.new { puts Rails.cache.fetch('a', expires_in: 2.seconds) { rand } }, 
  Thread.new { puts Rails.cache.fetch('a', expires_in: 2.seconds) { rand } } 
]

我认为您的Rails配置正在使用文件进行缓存(为确保这一点，请检查Rails应用程序中的/tmp/cache文件夹).

I think your rails configuration is using file for caching (to ensure that, pls check the folder /tmp/cache in your rails app).

由于'Rails.cache'需要执行从文件读取缓存的操作，因此非常耗时，并且两个线程中的'fetch'操作大部分都在同一时间运行，因此'a'值不存在或为已经过期.

Because 'Rails.cache' needs to perform reading cache from file, it is time-consuming, and the action 'fetch' in 2 threads mostly run at the same time, so 'a' value doesn't exist or is expired already.

在第二个代码块中

[  
  Thread.new { sleep(1); puts Rails.cache.fetch('a', expires_in: 2.seconds) { rand } }, 
  Thread.new { puts Rails.cache.fetch('a', expires_in: 2.seconds) { rand } } 
]

当第一个线程尝试获取'a'时，'a'已经在缓存文件中.这就是它起作用的原因.

When the first thread tries to fetch 'a', 'a' is in cache file already. So that is why it works.

让我们进行另一个模拟，而不是使用"Rails.cache"，我们将使用MemoryStore缓存，如下所示:

Let make another simulation, instead of using 'Rails.cache', we will use MemoryStore cache like this:

cache = ActiveSupport::Cache::MemoryStore.new(expires_in: 5.minutes)
[
  Thread.new { puts cache.fetch('a', expires_in: 2.seconds) { rand } },
  Thread.new { puts cache.fetch('a', expires_in: 2.seconds) { rand } }
]

它也符合我们的期望！

这篇关于Rails.cache在不同的线程中不能缓存?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！