Known Issues

Occasionally odd issues arise without a transparent or acceptable solution. Those issues are documented here.

• When using “preload_app true”, with apps using background threads need to restart them in the after_fork hook because threads are never shared with child processes. Additionally, any synchronization primitives (Mutexes, Monitors, ConditionVariables) should be reinitialized in case they are held during fork time to avoid deadlocks. The core Ruby Logger class needlessly uses a MonitorMutex which can be disabled with a monkey patch
• Rails 2.3.2 bundles its own version of Rack. This may cause subtle bugs when simultaneously loaded with the system-wide Rack Rubygem which Unicorn depends on. Upgrading to Rails 2.3.4 (or later) is strongly recommended for all Rails 2.3.x users for this (and security reasons). Rails 2.2.x series (or before) did not bundle Rack and are should be unnaffected. If there is any reason which forces your application to use Rails 2.3.2 and you have no other choice, then you may edit your Unicorn gemspec and remove the Rack dependency.

  ref: mid.gmane.org/20091014221552.GA30624@dcvr.yhbt.net Note: the workaround described in the article above only made the issue more subtle and we didn’t notice them immediately.

• Installing “unicorn” as a system-wide Rubygem and using the isolate gem may cause issues if you’re using any of the bundled application-level libraries in unicorn/app/* (for compatibility with CGI-based applications, Rails <= 2.2.2, or ExecCgi). For now workarounds include:
  • installing the same version of unicorn as a system-wide Rubygem and isolating unicorn as well.
  • explicitly setting RUBYLIB or $LOAD_PATH to include any gem path where the unicorn gem is installed (e.g. /usr/lib/ruby/gems/1.8/gems/unicorn-VERSION/lib)
• WONTFIX: code reloading and restarts with Sinatra 0.3.x (and likely older versions) apps is broken. The workaround is to force production mode to disable code reloading as well as disabling “run” in your Sinatra application:

    set :env, :production
    set :run, false
  

  Since this is no longer an issue with Sinatra 0.9.x apps, this will not be fixed on our end. Since Unicorn is itself the application launcher, the at_exit handler used in old Sinatra always caused Mongrel to be launched whenever a Unicorn worker was about to exit.

  Also remember we’re capable of replacing the running binary without dropping any connections regardless of framework :)

[Validate]

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