Add Pitchfork Memory Stats (#68)

* Add Memory Stats

* Conditionally use rack middlewares

* 💇‍♀️

* Remove after: :load_config_initializers block

* Revert "Remove after: :load_config_initializers block"

This reverts commit 58c9d9c.

* Disable metrics

* Use single block of initialization

Author: robertomiranda

lib/promenade/pitchfork/mem_stats.rb

@@ -0,0 +1,36 @@
+begin
+  require "pitchfork/mem_info"
+rescue LoadError
+  # No pitchfork available, dont do anything
+end
+
+module Promenade
+  module Pitchfork
+    class MemStats
+      Promenade.gauge :pitchfork_mem_rss do
+        doc "Resident Set Size of the pitchfork process, Total memory used by the process."
+      end
+
+      Promenade.gauge :pitchfork_shared_mem do
+        doc "Shared memory of the pitchfork process, memory that is shared between multiple processes."
+      end
+
+      def initialize
+        return unless defined?(::Pitchfork) && defined?(::Pitchfork::MemInfo)
+
+        @mem_info = ::Pitchfork::MemInfo.new(Process.pid)
+        @parent_mem_info = ::Pitchfork::MemInfo.new(Process.ppid)
+      end
+
+      def instrument
+        Promenade.metric(:pitchfork_mem_rss).set({}, @mem_info.rss)
+        Promenade.metric(:pitchfork_shared_mem).set({}, @mem_info.shared_memory)
+      end
+
+      def self.instrument
+        new.instrument
+      rescue StandardError
+      end
+    end
+  end
+end

lib/promenade/pitchfork/middleware.rb

@@ -1,4 +1,5 @@
 require "promenade/pitchfork/stats"
+require "promenade/pitchfork/mem_stats"
 
 module Promenade
   module Pitchfork
@@ -11,12 +12,17 @@ def initialize(app)
 
       def call(env)
         if env.key?(RACK_AFTER_REPLY)
-          env[RACK_AFTER_REPLY] << -> {
-            ::Promenade::Pitchfork::Stats.instrument
-          }
+          env[RACK_AFTER_REPLY] << -> { instrument }
         end
         @app.call(env)
       end
+
+      private
+
+        def instrument
+          Promenade::Pitchfork::Stats.instrument
+          Promenade::Pitchfork::MemStats.instrument
+        end
     end
   end
 end

spec/promenade/pitchfork/mem_stats_spec.rb

@@ -0,0 +1,34 @@
+require "spec_helper"
+require "promenade/pitchfork/mem_stats"
+
+RSpec.describe Promenade::Pitchfork::MemStats do
+  let(:pitfork_mem_info) { class_double("Pitchfork::MemInfo") }
+
+  before do
+    stub_const("Pitchfork::MemInfo", pitfork_mem_info)
+    allow(pitfork_mem_info).to receive(:new).and_return(pitfork_mem_info)
+    allow(pitfork_mem_info).to receive(:rss).and_return(100)
+    allow(pitfork_mem_info).to receive(:shared_memory).and_return(50)
+  end
+
+  describe "#instrument" do
+    let(:metric) { instance_double("Promenade::Metric") }
+
+    before do
+      allow(Promenade).to receive(:metric).and_return(metric)
+      allow(metric).to receive(:set)
+    end
+
+    it "sets the metrics correctly" do
+      stats = Promenade::Pitchfork::MemStats.new
+
+      expect(Promenade).to receive(:metric).with(:pitchfork_mem_rss).and_return(metric)
+      expect(Promenade).to receive(:metric).with(:pitchfork_shared_mem).and_return(metric)
+
+      expect(metric).to receive(:set).with({}, 100)
+      expect(metric).to receive(:set).with({}, 50)
+
+      stats.instrument
+    end
+  end
+end