Use constants instead of getters

lib/gitlab/sidekiq_middleware/memory_killer.rb

 module Gitlab
   module SidekiqMiddleware
     class MemoryKiller
+      # Default the RSS limit to 0, meaning the MemoryKiller is disabled
+      MAX_RSS = (ENV['SIDEKIQ_MEMORY_KILLER_MAX_RSS'] || 0).to_s.to_i
       # Give Sidekiq 15 minutes of grace time after exceeding the RSS limit
-      GRACE_TIME = 15 * 60
+      GRACE_TIME = (ENV['SIDEKIQ_MEMORY_KILLER_GRACE_TIME'] || 15 * 60).to_s.to_i
       # Wait 30 seconds for running jobs to finish during graceful shutdown
-      SHUTDOWN_WAIT = 30
-      # Create a mutex so that there will be only one thread waiting to shut
-      # Sidekiq down
+      SHUTDOWN_WAIT = (ENV['SIDEKIQ_MEMORY_KILLER_SHUTDOWN_WAIT'] || 30).to_s.to_i
+
+      # Create a mutex used to ensure there will be only one thread waiting to
+      # shut Sidekiq down
       MUTEX = Mutex.new
 
       def call(worker, job, queue)
         yield
         current_rss = get_rss
 
-        return unless max_rss > 0 && current_rss > max_rss
+        return unless MAX_RSS > 0 && current_rss > MAX_RSS
 
         Tread.new do
           # Return if another thread is already waiting to shut Sidekiq down
           return unless MUTEX.try_lock
 
           Sidekiq.logger.warn "current RSS #{current_rss} exceeds maximum RSS "\
-            "#{max_rss}"
+            "#{MAX_RSS}"
           Sidekiq.logger.warn "spawned thread that will shut down PID "\
-            "#{Process.pid} in #{grace_time} seconds"
-          sleep(grace_time)
+            "#{Process.pid} in #{GRACE_TIME} seconds"
+          sleep(GRACE_TIME)
 
           Sidekiq.logger.warn "sending SIGUSR1 to PID #{Process.pid}"
           Process.kill('SIGUSR1', Process.pid)
 
-          Sidekiq.logger.warn "waiting #{shutdown_wait} seconds before sending "\
+          Sidekiq.logger.warn "waiting #{SHUTDOWN_WAIT} seconds before sending "\
             "SIGTERM to PID #{Process.pid}"
-          sleep(shutdown_wait)
+          sleep(SHUTDOWN_WAIT)
 
           Sidekiq.logger.warn "sending SIGTERM to PID #{Process.pid}"
           Process.kill('SIGTERM', Process.pid)
@@ -45,22 +48,6 @@ module Gitlab
 
         output.to_i
       end
-
-      def max_rss
-        @max_rss ||= ENV['SIDEKIQ_MAX_RSS'].to_s.to_i
-      end
-
-      def shutdown_wait
-        @graceful_shutdown_wait ||= (
-          ENV['SIDEKIQ_MEMORY_KILLER_SHUTDOWN_WAIT'] || SHUTDOWN_WAIT
-        ).to_i
-      end
-
-      def grace_time
-        @grace_time ||= (
-          ENV['SIDEKIQ_MEMORY_KILLER_GRACE_TIME'] || GRACE_TIME
-        ).to_i
-      end
     end
   end
 end