Improve performance of the log subscriber by remembering the list of all...

Improve performance of the log subscriber by remembering the list of all loggers instead of trying to extract them each time

railties/lib/rails/log_subscriber.rb

@@ -52,6 +52,7 @@ class LogSubscriber
 
     def self.add(namespace, log_subscriber, notifier = ActiveSupport::Notifications)
       log_subscribers << log_subscriber
+      @flushable_loggers = nil
 
       log_subscriber.public_methods(false).each do |event|
         notifier.subscribe("#{event}.#{namespace}") do |*args|
@@ -70,11 +71,17 @@ def self.log_subscribers
       @log_subscribers ||= []
     end
 
+    def self.flushable_loggers
+      @flushable_loggers ||= begin
+        loggers = log_subscribers.map(&:logger)
+        loggers.uniq!
+        loggers.select { |l| l.respond_to?(:flush) }
+      end
+    end
+
     # Flush all log_subscribers' logger.
     def self.flush_all!
-      loggers = log_subscribers.map(&:logger)
-      loggers.uniq!
-      loggers.each { |l| l.flush if l.respond_to?(:flush) }
+      flushable_loggers.each(&:flush)
     end
 
     # By default, we use the Rails.logger for logging.