DEV: Warn if distributed-mutexing in a request

app/controllers/application_controller.rb

@@ -29,6 +29,7 @@ class ApplicationController < ActionController::Base
     end
   end
 
+  before_action :set_thread_variable
   before_action :rate_limit_crawlers
   before_action :check_readonly_mode
   before_action :handle_theme
@@ -56,6 +57,10 @@ class ApplicationController < ActionController::Base
 
   layout :set_layout
 
+  def set_thread_variable
+    Thread.current["_in_request"] = true
+  end
+
   def has_escaped_fragment?
     SiteSetting.enable_escaped_fragments? && params.key?("_escaped_fragment_")
   end

lib/distributed_mutex.rb

@@ -48,6 +48,7 @@ class DistributedMutex
 
   # NOTE wrapped in mutex to maintain its semantics
   def synchronize
+    Rails.logger.warn("DistributedMutex.synchronize called inside a request lifecycle") if Thread.current["_in_request"]
     result = nil
 
     @mutex.synchronize do