diff --git a/lib/i18n/tasks/logging.rb b/lib/i18n/tasks/logging.rb
index <HASH>..<HASH> 100644
--- a/lib/i18n/tasks/logging.rb
+++ b/lib/i18n/tasks/logging.rb
@@ -25,6 +25,9 @@ module I18n::Tasks::Logging
 
   def log_stderr(*args)
     MUTEX.synchronize do
+      # 1. We don't want output from different threads to get intermixed.
+      # 2. StringIO is currently not thread-safe (blows up) on JRuby:
+      # https://github.com/jruby/jruby/issues/4417
       $stderr.puts(*args)
     end
   end
Explain on why the mutex is needed in logging.rb

Reference <URL>