如何消除Rails中'actor already terminated (Celluloid::DeadActorError)'警告

问题场景 #

使用Ctrl + C停止Rails开发服务器时，出现actor already terminated (Celluloid::DeadActorError)警告。环境配置：

• Rails版本：6.1.7
• Ruby版本：3.2.2
• Puma版本：5.6.7
• 当前启用config.file_watcher = ActiveSupport::EventedFileUpdateChecker作为文件监视器

注释掉config/environments/development.rb中的config.file_watcher = ActiveSupport::EventedFileUpdateChecker可消除警告，但此方法会降级到轮询式文件检查，不推荐长期使用。

错误堆栈 #

=> Run `bin/rails server --help` for more startup options
Puma starting in single mode...
* Puma version: 5.6.7 (ruby 3.2.2-p53) ("Birdie's Version")
*  Min threads: 0
*  Max threads: 5
*  Environment: development
*          PID: 12486
* Listening on http://127.0.0.1:3000
* Listening on http://[::1]:3000
Use Ctrl-C to stop
^C- Gracefully stopping, waiting for requests to finish
=== puma shutdown: 2023-11-07 15:39:16 +0530 ===
- Goodbye!
Exiting
bin/rails: warning: Exception in finalizer #<Proc:0x00007f905e3741f0 /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/activesupport-6.1.7/lib/active_support/evented_file_update_checker.rb:93>
/home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/celluloid-0.16.0/lib/celluloid/proxies/actor_proxy.rb:34:in `terminate!': actor already terminated (Celluloid::DeadActorError)
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/celluloid-0.16.0/lib/celluloid/proxies/actor_proxy.rb:27:in `terminate'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/celluloid-0.16.0/lib/celluloid/proxies/cell_proxy.rb:60:in `terminate'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/listen-2.10.1/lib/listen/listener.rb:76:in `block in <class:Listener>'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/celluloid-0.16.0/lib/celluloid/fsm.rb:175:in `instance_eval'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/celluloid-0.16.0/lib/celluloid/fsm.rb:175:in `call'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/celluloid-0.16.0/lib/celluloid/fsm.rb:127:in `transition_with_callbacks!'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/celluloid-0.16.0/lib/celluloid/fsm.rb:95:in `transition'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/listen-2.10.1/lib/listen/listener.rb:108:in `stop'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/activesupport-6.1.7/lib/active_support/evented_file_update_checker.rb:113:in `stop'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/activesupport-6.1.7/lib/active_support/evented_file_update_checker.rb:94:in `block in finalizer'
bin/rails: warning: Exception in finalizer #<Proc:0x00007f90617787d0 /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/activesupport-6.1.7/lib/active_support/evented_file_update_checker.rb:93>
/home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/celluloid-0.16.0/lib/celluloid/proxies/actor_proxy.rb:34:in `terminate!': actor already terminated (Celluloid::DeadActorError)
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/celluloid-0.16.0/lib/celluloid/proxies/actor_proxy.rb:27:in `terminate'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/celluloid-0.16.0/lib/celluloid/proxies/cell_proxy.rb:60:in `terminate'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/listen-2.10.1/lib/listen/listener.rb:76:in `block in <class:Listener>'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/celluloid-0.16.0/lib/celluloid/fsm.rb:175:in `instance_eval'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/celluloid-0.16.0/lib/celluloid/fsm.rb:175:in `call'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/celluloid-0.16.0/lib/celluloid/fsm.rb:127:in `transition_with_callbacks!'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/celluloid-0.16.0/lib/celluloid/fsm.rb:95:in `transition'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/listen-2.10.1/lib/listen/listener.rb:108:in `stop'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/activesupport-6.1.7/lib/active_support/evented_file_update_checker.rb:113:in `stop'
    from /home/xxxx/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/activesupport-6.1.7/lib/active_support/evented_file_update_checker.rb:94:in `block in finalizer'

原因分析 #

警告源于ActiveSupport::EventedFileUpdateChecker依赖的旧版本listen gem（2.10.1）与celluloid 0.16.0在Ruby 3.2+下的终止逻辑冲突。Ruby 3.2调整了finalizer执行时机，导致监听器的actor被重复调用terminate方法，触发DeadActorError。

解决方案 #

1. 更新listen gem（推荐） #

Rails 6.1.x兼容listen 3.x版本，该版本已移除对celluloid的依赖，从根源解决冲突：

• 在Gemfile中添加或修改：

  gem 'listen', '~> 3.7'
  

• 执行更新命令：

  bundle update listen
  

2. 修补EventedFileUpdateChecker的终止逻辑（临时方案） #

如果暂时无法更新gem，可修改active_support/evented_file_update_checker.rb的finalizer代码，捕获DeadActorError避免警告：

• 找到本地gem对应文件（路径示例：~/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/activesupport-6.1.7/lib/active_support/evented_file_update_checker.rb）
• 修改finalizer方法：

  def finalizer
    proc do
      stop rescue Celluloid::DeadActorError
    end
  end
  

注意：修改本地gem文件会在gem更新后失效，建议使用patch gem持久化补丁。

3. 降级文件监视器（不推荐） #

注释掉config/environments/development.rb中的以下配置：

# config.file_watcher = ActiveSupport::EventedFileUpdateChecker

此方法会 fallback到轮询式的ActiveSupport::FileUpdateChecker，虽能消除警告，但文件变更检测效率会降低。

内容的提问来源于stack exchange，提问作者suyogb