Fixes #39277 - Fix TopbarSweeper thread-safety race condition

TopbarSweeper uses a Singleton with a shared controller attribute
across all Puma threads. Under concurrent requests, one thread ensure
block nils the controller while another thread is still using it,
causing NoMethodError on expire_fragment.

Replace the Singleton with Thread.current storage, following the same
pattern used by ThreadSession for User.current/Organization.current.
Each thread gets its own controller reference - no cross-thread
clobbering.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: pablomh

app/controllers/concerns/foreman/controller/topbar_sweeper.rb

@@ -8,10 +8,10 @@ module TopbarSweeper
       end
 
       def set_topbar_sweeper_controller
-        ::TopbarSweeper.instance.controller = self
+        ::TopbarSweeper.controller = self
         yield
       ensure
-        ::TopbarSweeper.instance.controller = nil
+        ::TopbarSweeper.controller = nil
       end
     end
   end

app/models/concerns/topbar_cache_expiry.rb

@@ -8,6 +8,6 @@ module TopbarCacheExpiry
   end
 
   def expire_topbar_cache_within_controller
-    expire_topbar_cache if TopbarSweeper.instance.controller.present?
+    expire_topbar_cache if TopbarSweeper.controller
   end
 end

app/services/topbar_sweeper.rb

@@ -1,13 +1,18 @@
 class TopbarSweeper
-  include Singleton
-  attr_accessor :controller
-
-  def expire_cache(user = User.current)
-    controller.expire_fragment(self.class.fragment_name(user.id)) if controller.present? && user.present?
-  end
+  THREAD_KEY = :topbar_sweeper_controller
 
   class << self
-    delegate :expire_cache, to: :instance
+    def controller
+      Thread.current[THREAD_KEY]
+    end
+
+    def controller=(ctrl)
+      Thread.current[THREAD_KEY] = ctrl
+    end
+
+    def expire_cache(user = User.current)
+      controller&.expire_fragment(fragment_name(user.id)) if user.present?
+    end
 
     def fragment_name(id = User.current.id)
       "tabs_and_title_records-#{id}"

test/unit/topbar_sweeper_test.rb

@@ -0,0 +1,30 @@
+require 'test_helper'
+
+class TopbarSweeperTest < ActiveSupport::TestCase
+  def teardown
+    TopbarSweeper.controller = nil
+  end
+
+  test "controller is thread-local" do
+    TopbarSweeper.controller = "main"
+    thread_value = nil
+    Thread.new { thread_value = TopbarSweeper.controller }.join
+    assert_nil thread_value, "Other thread should not see main thread's controller"
+    assert_equal "main", TopbarSweeper.controller
+  end
+
+  test "expire_cache calls expire_fragment on controller" do
+    mock_controller = Minitest::Mock.new
+    user = FactoryBot.create(:user)
+    mock_controller.expect :expire_fragment, nil, [TopbarSweeper.fragment_name(user.id)]
+    TopbarSweeper.controller = mock_controller
+    TopbarSweeper.expire_cache(user)
+    mock_controller.verify
+  end
+
+  test "expire_cache does not raise when controller is nil" do
+    TopbarSweeper.controller = nil
+    user = FactoryBot.create(:user)
+    assert_nothing_raised { TopbarSweeper.expire_cache(user) }
+  end
+end