1 files changed, 94 insertions, 0 deletions
diff --git a/lib/gitlab/metrics/base_sampler.rb b/lib/gitlab/metrics/base_sampler.rb
new file mode 100644
index 00000000000..219accfc029
--- /dev/null
+++ b/lib/gitlab/metrics/base_sampler.rb
@@ -0,0 +1,94 @@
+require 'logger'
+module Gitlab
+  module Metrics
+    class BaseSampler
+      def self.initialize_instance(*args)
+        raise "#{name} singleton instance already initialized" if @instance
+        @instance = new(*args)
+        at_exit(&@instance.method(:stop))
+        @instance
+      end
+
+      def self.instance
+        @instance
+      end
+
+      attr_reader :running
+
+      # interval - The sampling interval in seconds.
+      def initialize(interval)
+        interval_half = interval.to_f / 2
+
+        @interval = interval
+        @interval_steps = (-interval_half..interval_half).step(0.1).to_a
+
+        @mutex = Mutex.new
+      end
+
+      def enabled?
+        true
+      end
+
+      def start
+        return unless enabled?
+
+        @mutex.synchronize do
+          return if running
+          @running = true
+
+          @thread = Thread.new do
+            sleep(sleep_interval)
+
+            while running
+              safe_sample
+
+              sleep(sleep_interval)
+            end
+          end
+        end
+      end
+
+      def stop
+        @mutex.synchronize do
+          return unless running
+
+          @running = false
+
+          if @thread
+            @thread.wakeup if @thread.alive?
+            @thread.join
+            @thread = nil
+          end
+        end
+      end
+
+      def safe_sample
+        sample
+      rescue => e
+        Rails.logger.warn("#{self.class}: #{e}, stopping")
+        stop
+      end
+
+      def sample
+        raise NotImplementedError
+      end
+
+      # Returns the sleep interval with a random adjustment.
+      #
+      # The random adjustment is put in place to ensure we:
+      #
+      # 1. Don't generate samples at the exact same interval every time (thus
+      #    potentially missing anything that happens in between samples).
+      # 2. Don't sample data at the same interval two times in a row.
+      def sleep_interval
+        while step = @interval_steps.sample
+          if step != @last_step
+            @last_step = step
+
+            return @interval + @last_step
+          end
+        end
+      end
+    end
+  end
+end