sdk_keys singleton check

lib/configcat/configcatclient.rb

@@ -10,6 +10,8 @@
 module ConfigCat
   KeyValue = Struct.new(:key, :value)
   class ConfigCatClient
+    @@sdk_keys = []
+
     def initialize(sdk_key,
                    poll_interval_seconds:60,
                    max_init_wait_time_seconds:5,
@@ -27,6 +29,15 @@ def initialize(sdk_key,
       if sdk_key === nil
         raise ConfigCatClientException, "SDK Key is required."
       end
+
+      if @@sdk_keys.include?(sdk_key)
+        ConfigCat.logger.warn("A ConfigCat Client is already initialized with sdk_key %s. "\
+                              "We strongly recommend you to use the ConfigCat Client as "\
+                              "a Singleton object in your application." % sdk_key)
+      else
+        @@sdk_keys.push(sdk_key)
+      end
+
       @_sdk_key = sdk_key
 
       if config_cache_class
@@ -144,6 +155,7 @@ def force_refresh()
     def stop()
       @_cache_policy.stop()
       @_config_fetcher.close()
+      @@sdk_keys.delete(@_sdk_key)
     end
 
     private

samples/consolesample2.rb

@@ -16,4 +16,6 @@
 puts("'isPOCFeatureEnabled' value from ConfigCat: " + value.to_s)
 
 value = client.get_value("isAwesomeFeatureEnabled", "default value")
-puts("'isAwesomeFeatureEnabled' value from ConfigCat: " + value.to_s)
+puts("'isAwesomeFeatureEnabled' value from ConfigCat: " + value.to_s)
+
+client.stop()