Move prometheus metrics to module. Use class instance variables for metrics...

Move prometheus metrics to module. Use class instance variables for metrics and metrics cache in metrics concern

lib/gitlab/metrics.rb

 module Gitlab
   module Metrics
     extend Gitlab::Metrics::InfluxDb
-    extend Gitlab::Metrics::Prometheus
+    include Gitlab::Metrics::Prometheus
 
     def self.enabled?
       influx_metrics_enabled? || prometheus_metrics_enabled?

lib/gitlab/metrics/concern.rb

@@ -6,12 +6,13 @@ module Gitlab
       extend ActiveSupport::Concern
 
       included do
-        @@_metric_provider_mutex = Mutex.new
+        @_metric_provider_mutex = Mutex.new
+        @_metrics_provider_cache = {}
       end
 
       class_methods do
         def reload_metric!(name)
-          @_metrics_provider_cache&.delete(name)
+          @_metrics_provider_cache.delete(name)
         end
 
         private
@@ -22,12 +23,12 @@ module Gitlab
           end
 
           define_singleton_method(name) do
-            @_metrics_provider_cache&.[](name) || init_metric(type, name, opts, &block)
+            @_metrics_provider_cache[name] || init_metric(type, name, opts, &block)
           end
         end
 
         def fetch_metric(type, name, opts = {}, &block)
-          @_metrics_provider_cache&.[](name) || init_metric(type, name, opts, &block)
+          @_metrics_provider_cache[name] || init_metric(type, name, opts, &block)
         end
 
         def init_metric(type, name, opts = {}, &block)
@@ -42,8 +43,7 @@ module Gitlab
         end
 
         def synchronized_cache_fill(key)
-          @@_metric_provider_mutex.synchronize do
-            @_metrics_provider_cache ||= {}
+          @_metric_provider_mutex.synchronize do
             @_metrics_provider_cache[key] ||= yield
           end
         end

lib/gitlab/metrics/influx_db.rb

 module Gitlab
   module Metrics
     module InfluxDb
-      include Gitlab::Metrics::Concern::ClassMethods
+      include Gitlab::Metrics::Concern
       include Gitlab::CurrentSettings
       extend self
 

lib/gitlab/metrics/prometheus.rb

@@ -3,12 +3,16 @@ require 'prometheus/client'
 module Gitlab
   module Metrics
     module Prometheus
+      extend ActiveSupport::Concern
+      include Gitlab::Metrics::Concern
       include Gitlab::CurrentSettings
-      include Gitlab::Utils::StrongMemoize
 
       REGISTRY_MUTEX = Mutex.new
       PROVIDER_MUTEX = Mutex.new
 
+      class_methods do
+        include Gitlab::Utils::StrongMemoize
+
         def metrics_folder_present?
           multiprocess_files_dir = ::Prometheus::Client.configuration.multiprocess_files_dir
 
@@ -73,4 +77,5 @@ module Gitlab
         end
       end
     end
+  end
 end