use handle continue for heavy lifting, copied from deadtrickster#150

elvis.config

@@ -20,11 +20,12 @@
                    #{ignore => [
                                 prometheus_misc,
                                 prometheus_registry,
-                                prometheus_sup,
+                                prometheus_startup,
                                 prometheus_instrumenter
                                ]}},
                   {elvis_style, god_modules, #{limit => 54}},
-                  {elvis_style, dont_repeat_yourself, #{min_complexity => 50}}
+                  {elvis_style, dont_repeat_yourself, #{min_complexity => 50}},
+                  {elvis_style, state_record_and_type, #{ignore => [prometheus_startup]}}
                  ],
         ruleset => erl_files
        },
@@ -80,4 +81,4 @@
     }
    ]
  }
-].
+].

src/prometheus_startup.erl

@@ -0,0 +1,107 @@
+-module(prometheus_startup).
+
+-behaviour(gen_server).
+
+-include("prometheus.hrl").
+
+-export([start_link/0]).
+-export([init/1, handle_continue/2, handle_call/3, handle_cast/2, handle_info/2,
+         terminate/2, code_change/3]).
+-export([register_metrics/1]).
+
+start_link() ->
+  gen_server:start_link(?MODULE, [], []).
+
+%%% Server functions
+init([]) ->
+  create_tables(),
+  {ok, [], {continue, []}}.
+
+handle_continue(_Continue, _State) ->
+  register_collectors(),
+  register_metrics(),
+  setup_instrumenters(),
+  {noreply, []}.
+
+%% Gen Server boilerplate
+
+handle_call(_Request, _From, State) ->
+  {reply, ignored, State}.
+
+handle_cast(_Msg, State) ->
+  {noreply, State}.
+
+handle_info(_Info, State) ->
+  {noreply, State}.
+
+terminate(_Reason, _State) ->
+  ok.
+
+code_change(_OldVsn, State, _Extra) ->
+  {ok, State}.
+
+%%% Private functions
+
+create_tables() ->
+  Tables =
+    [{?PROMETHEUS_REGISTRY_TABLE, {bag, read_concurrency}},
+     {?PROMETHEUS_COUNTER_TABLE, write_concurrency},
+     {?PROMETHEUS_GAUGE_TABLE, write_concurrency},
+     {?PROMETHEUS_SUMMARY_TABLE, write_concurrency},
+     {?PROMETHEUS_QUANTILE_SUMMARY_TABLE, write_concurrency},
+     {?PROMETHEUS_HISTOGRAM_TABLE, write_concurrency},
+     {?PROMETHEUS_BOOLEAN_TABLE, write_concurrency}],
+  [maybe_create_table(Name, Concurrency) || {Name, Concurrency} <- Tables],
+  ok.
+
+register_collectors() ->
+  Collectors = prometheus_collector:enabled_collectors(),
+  prometheus_registry:register_collectors(Collectors).
+
+register_metrics() ->
+  [declare_metric(Decl) || Decl <- default_metrics()].
+
+register_metrics(Metrics) ->
+  DefaultMetrics0 = default_metrics(),
+  DefaultMetrics1 = lists:usort(DefaultMetrics0 ++ Metrics),
+  application:set_env(prometheus, default_metrics, DefaultMetrics1),
+  [declare_metric(Decl) || Decl <- Metrics].
+
+setup_instrumenters() ->
+  [prometheus_instrumenter:setup(Instrumenter)
+   || Instrumenter <- prometheus_instrumenter:enabled_instrumenters()].
+
+default_metrics() ->
+  application:get_env(prometheus, default_metrics, []).
+
+maybe_create_table(Name, {Type, Concurrency}) ->
+  case ets:info(Name) of
+    undefined ->
+      ets:new(Name, [Type, named_table, public, {Concurrency, true}]);
+    _ ->
+      ok
+  end;
+maybe_create_table(Name, Concurrency) ->
+  maybe_create_table(Name, {set, Concurrency}).
+
+declare_metric({Metric, Spec}) ->
+  declare_metric(Metric, Spec);
+declare_metric({Registry, Metric, Spec}) ->
+  declare_metric(Metric, [{registry, Registry}] ++ Spec).
+
+declare_metric(Metric, Spec) ->
+  Module = type_to_module(Metric),
+  Module:declare(Spec).
+
+type_to_module(counter) ->
+  prometheus_counter;
+type_to_module(gauge) ->
+  prometheus_gauge;
+type_to_module(summary) ->
+  prometheus_summary;
+type_to_module(histogram) ->
+  prometheus_histogram;
+type_to_module(boolean) ->
+  prometheus_boolean;
+type_to_module(Type) ->
+  Type.

src/prometheus_sup.erl

@@ -9,12 +9,9 @@
 -export([start_link/0]).
 %% Supervisor callbacks
 -export([init/1]).
--export([register_metrics/1]).
 
 -behaviour(supervisor).
 
--include("prometheus.hrl").
-
 %%====================================================================
 %% Macros
 %%====================================================================
@@ -34,77 +31,11 @@ start_link() ->
 
 %% Child :: {Id,StartFunc,Restart,Shutdown,Type,Modules}
 init([]) ->
-  create_tables(),
-  register_collectors(),
-  register_metrics(),
-  setup_instrumenters(),
-  {ok, {{one_for_one, 5, 1}, []}}.
-
-%%====================================================================
-%% Private Parts
-%%====================================================================
-
-create_tables() ->
-  Tables = [
-            {?PROMETHEUS_REGISTRY_TABLE, {bag, read_concurrency}},
-            {?PROMETHEUS_COUNTER_TABLE, write_concurrency},
-            {?PROMETHEUS_GAUGE_TABLE, write_concurrency},
-            {?PROMETHEUS_SUMMARY_TABLE, write_concurrency},
-            {?PROMETHEUS_QUANTILE_SUMMARY_TABLE, write_concurrency},
-            {?PROMETHEUS_HISTOGRAM_TABLE, write_concurrency},
-            {?PROMETHEUS_BOOLEAN_TABLE, write_concurrency}
-           ],
-  [maybe_create_table(Name, Concurrency) || {Name, Concurrency} <- Tables],
-  ok.
-
-register_collectors() ->
-  Collectors = prometheus_collector:enabled_collectors(),
-  prometheus_registry:register_collectors(Collectors).
-
-register_metrics() ->
-  [declare_metric(Decl) || Decl <- default_metrics()].
-
-register_metrics(Metrics) ->
-  DefaultMetrics0 = default_metrics(),
-  DefaultMetrics1 = lists:usort(DefaultMetrics0 ++ Metrics),
-  application:set_env(prometheus, default_metrics, DefaultMetrics1),
-  [declare_metric(Decl) || Decl <- Metrics].
-
-setup_instrumenters() ->
-  [prometheus_instrumenter:setup(Instrumenter) ||
-    Instrumenter <- prometheus_instrumenter:enabled_instrumenters()].
-
-default_metrics() ->
-  application:get_env(prometheus, default_metrics, []).
-
-maybe_create_table(Name, {Type, Concurrency}) ->
-  case ets:info(Name) of
-    undefined ->
-      ets:new(Name, [Type, named_table, public, {Concurrency, true}]);
-    _ ->
-      ok
-  end;
-maybe_create_table(Name, Concurrency) ->
-  maybe_create_table(Name, {set, Concurrency}).
-
-declare_metric({Metric, Spec}) ->
-  declare_metric(Metric, Spec);
-declare_metric({Registry, Metric, Spec}) ->
-  declare_metric(Metric, [{registry, Registry}] ++ Spec).
-
-declare_metric(Metric, Spec) ->
-  Module = type_to_module(Metric),
-  Module:declare(Spec).
-
-type_to_module(counter) ->
-  prometheus_counter;
-type_to_module(gauge) ->
-  prometheus_gauge;
-type_to_module(summary) ->
-  prometheus_summary;
-type_to_module(histogram) ->
-  prometheus_histogram;
-type_to_module(boolean) ->
-  prometheus_boolean;
-type_to_module(Type) ->
-  Type.
+  ChildSpec =
+    [{prometheus_startup_server,
+      {prometheus_startup, start_link, []},
+      permanent,
+      1000,
+      worker,
+      [prometheus_startup]}],
+  {ok, {{one_for_one, 5, 1}, ChildSpec}}.

test/eunit/prometheus_default_metrics_tests.erl

@@ -5,27 +5,24 @@
 default_metric_test() ->
   try
     Name = metric_name,
-    Spec = [{name, Name},
-            {help, ""},
-            {registry, qwe},
-            {buckets, [1, 2, 3]}],
-    Spec1 = [{name, Name},
-             {help, ""},
-             {buckets, [1, 2, 3]}],
+    Spec = [{name, Name}, {help, ""}, {registry, qwe}, {buckets, [1, 2, 3]}],
+    Spec1 = [{name, Name}, {help, ""}, {buckets, [1, 2, 3]}],
 
     application:stop(prometheus),
-    application:set_env(prometheus, default_metrics,
+    application:set_env(prometheus,
+                        default_metrics,
                         [{counter, Spec},
                          {gauge, Spec},
                          {qwe, summary, Spec1},
                          {prometheus_histogram, Spec},
                          {boolean, Spec}]),
     application:start(prometheus),
+    timer:sleep(1000),
     ?assertEqual(false, prometheus_counter:declare(Spec)),
     ?assertEqual(false, prometheus_gauge:declare(Spec)),
     ?assertEqual(false, prometheus_summary:declare([{registry, qwe}] ++ Spec)),
     ?assertEqual(false, prometheus_histogram:declare(Spec)),
     ?assertEqual(false, prometheus_boolean:declare(Spec))
   after
     application:unset_env(prometheus, default_metrics)
-  end.
+  end.