cattr_accessor is not threadsafe!

app/controllers/application_controller.rb

 class ApplicationController < ActionController::Base
   before_filter :authenticate_user!
   before_filter :reject_blocked!
-  before_filter :set_current_user_for_observers
+  before_filter :set_current_user_for_thread
   before_filter :add_abilities
   before_filter :dev_tools if Rails.env == 'development'
   before_filter :default_headers
@@ -47,9 +47,8 @@ class ApplicationController < ActionController::Base
     end
   end
-  def set_current_user_for_observers
-    MergeRequestObserver.current_user = current_user
-    IssueObserver.current_user = current_user
+  def set_current_user_for_thread
+    Thread.current[:current_user] = current_user
   end
   def abilities

app/observers/base_observer.rb

@@ -6,4 +6,8 @@ class BaseObserver < ActiveRecord::Observer
   def log_info message
     Gitlab::AppLogger.info message
   end
+
+  def current_user
+    Thread.current[:current_user]
+  end
 end

app/observers/issue_observer.rb

 class IssueObserver < BaseObserver
-  cattr_accessor :current_user
-
   def after_create(issue)
     notification.new_issue(issue, current_user)
   end

app/observers/merge_request_observer.rb

 class MergeRequestObserver < BaseObserver
-  cattr_accessor :current_user
-
   def after_create(merge_request)
     notification.new_merge_request(merge_request, current_user)
   end

config/database.yml.mysql

@@ -6,7 +6,7 @@ production:
   encoding: utf8
   reconnect: false
   database: gitlabhq_production
-  pool: 5
+  pool: 10
   username: root
   password: "secure password"
   # host: localhost

config/database.yml.postgresql

@@ -5,7 +5,7 @@ production:
   adapter: postgresql
   encoding: unicode
   database: gitlabhq_production
-  pool: 5
+  pool: 10
   username: git
   password:
   # host: localhost

lib/api/issues.rb

@@ -2,6 +2,7 @@ module API
   # Issues API
   class Issues < Grape::API
     before { authenticate! }
+    before { Thread.current[:current_user] = current_user }
     resource :issues do
       # Get currently authenticated user's issues
@@ -79,7 +80,7 @@ module API
         attrs = attributes_for_keys [:title, :description, :assignee_id, :milestone_id, :state_event]
         attrs[:label_list] = params[:labels] if params[:labels].present?
-        IssueObserver.current_user = current_user
+
         if @issue.update_attributes attrs
           present @issue, with: Entities::Issue
         else

lib/api/merge_requests.rb

@@ -2,6 +2,7 @@ module API
   # MergeRequest API
   class MergeRequests < Grape::API
     before { authenticate! }
+    before { Thread.current[:current_user] = current_user }
     resource :projects do
       helpers do
@@ -94,8 +95,6 @@ module API
         authorize! :modify_merge_request, merge_request
-        MergeRequestObserver.current_user = current_user
-
         if merge_request.update_attributes attrs
           merge_request.reload_code
           merge_request.mark_as_unchecked

spec/models/milestone_spec.rb

@@ -39,7 +39,6 @@ describe Milestone do
     end
     it "should count closed issues" do
-      IssueObserver.current_user = issue.author
       issue.close
       milestone.issues << issue
       milestone.percent_complete.should == 100