Added threadsafe counting object

app/models/cluster.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+require 'securerandom'
+
+# A collective for a tally
+class Cluster
+  attr_reader :count, :name, :status, :uuid
+  @@clusters = {}
+
+  def initialize(name)
+    @uuid = SecureRandom.uuid
+    @name = name
+    @count = 0
+    @status = :open
+    @mutex = Mutex.new
+    @@clusters[@uuid] = self
+  end
+
+  def increment(var = 1)
+    @mutex.synchronize do
+      @count += var
+    end
+  end
+
+  def decrement(var = 1)
+    @mutex.synchronize do
+      @count -= var
+    end
+  end
+
+  class << self
+    def get(uuid)
+      @@clusters[uuid]
+    end
+
+    def list
+      @@clusters
+    end
+  end
+end

test/models/cluster_test.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+require 'concurrent/set'
+
+class ClusterTest < ActiveSupport::TestCase
+  test 'Cluster has instance record of all cluster' do
+    assert_equal 0, Cluster.list.size, 'starts off empty'
+    Cluster.new('foo')
+    Cluster.new('bar')
+    assert_equal 2, Cluster.list.size, 'Increases as more are added'
+  end
+
+  test 'cluster are addressable by the UUID' do
+    Cluster.new('bar')
+    cluster = Cluster.new('foo')
+    assert_equal cluster, Cluster.get(cluster.uuid)
+  end
+
+  test 'works' do
+    cluster = Cluster.new('foo')
+    cluster.increment
+    assert_equal 1, cluster.count
+    cluster.decrement
+    assert_equal 0, cluster.count
+  end
+
+  test 'is thread safe' do
+    cluster = Cluster.new('foo')
+    threads = []
+    (1..500).each { |_x| threads << Thread.new { cluster.increment } }
+    threads.each(&:join)
+
+    assert_equal 500, cluster.count
+  end
+end