KNOWN_ISSUES

= Known Issues

Occasionally odd {issues}[link:ISSUES.html] 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}[link:examples/logger_mp_safe.rb]

* 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: http://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}[http://github.com/jbarnette/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 :)