ConnectionPool adapter

Gemfile

@@ -28,6 +28,7 @@ gem 'mysql2'
 gem 'pg'
 gem 'cuprite'
 gem 'puma'
+gem 'connection_pool'
 
 group(:guard) do
   gem 'guard'

lib/flipper/adapter.rb

@@ -1,6 +1,20 @@
 module Flipper
   # Adding a module include so we have some hooks for stuff down the road
   module Adapter
+    OPERATIONS = [
+      :add,
+      :clear,
+      :disable,
+      :enable,
+      :export,
+      :features,
+      :get_all,
+      :get_multi,
+      :get,
+      :import,
+      :remove,
+    ]
+
     def self.included(base)
       base.extend(ClassMethods)
     end

lib/flipper/adapters/connection_pool.rb

@@ -0,0 +1,76 @@
+require "connection_pool"
+require "observer"
+
+# Make ConnectionPool observable so we can reset the cache when the pool is reloaded or shutdown
+ConnectionPool.class_eval do
+  module ShutdownObservable
+    def reload(&block)
+      super(&block).tap do
+        changed
+        notify_observers
+      end
+    end
+
+    def shutdown(&block)
+      super(&block).tap do
+        changed
+        notify_observers
+      end
+    end
+  end
+
+  include Observable
+  prepend ShutdownObservable
+end
+
+# An adapter that uses ConnectionPool to manage connections.
+#
+# Usage:
+#
+#   # Reuse an existing pool to create new adapters
+#   pool = ConnectionPool.new(size: 5, timeout: 5) { Redis.new }
+#   Flipper::Adapters::ConnectionPool.new(pool) do |client|
+#     Flipper::Adapters::Redis.new(client)
+#   end
+#
+#   # Create a new pool that returns the adapter
+#   Flipper::Adapters::ConnectionPool.new(size: 5, timeout: 5) do
+#     Flipper::Adapters::Redis.new(Redis.new)
+#   end
+class Flipper::Adapters::ConnectionPool
+  include Flipper::Adapter
+
+  # Use an existing ConnectionPool to initialize and cache new adapter instances.
+  class Wrapper
+    def initialize(pool, &initializer)
+      @pool = pool
+      @initializer = initializer
+      @instances = {}
+
+      # Reset the cache when the pool is reloaded or shutdown
+      @pool.add_observer(self, :reset)
+    end
+
+    def with(&block)
+      @pool.with do |resource|
+        yield @instances[resource] ||= @initializer.call(resource)
+      end
+    end
+
+    def reset
+      @instances.clear
+    end
+  end
+
+  attr_reader :pool
+
+  def initialize(options = {}, &adapter_initializer)
+    @pool = options.is_a?(ConnectionPool) ? Wrapper.new(options, &adapter_initializer) : ConnectionPool.new(options, &adapter_initializer)
+  end
+
+  OPERATIONS.each do |method|
+    define_method(method) do |*args|
+      @pool.with { |adapter| adapter.public_send(method, *args) }
+    end
+  end
+end

spec/flipper/adapters/connection_pool_spec.rb

@@ -0,0 +1,40 @@
+require "connection_pool"
+require "flipper/adapters/connection_pool"
+require "flipper-redis"
+
+RSpec.describe Flipper::Adapters::ConnectionPool do
+  let(:redis_options) { {url: ENV['REDIS_URL']}.compact }
+
+  before do
+    skip_on_error(Redis::CannotConnectError, 'Redis not available') do
+      Redis.new(redis_options).flushdb
+    end
+  end
+
+  context "with an existing pool" do
+    let(:pool) do
+      ConnectionPool.new(size: 1, timeout: 5) { Redis.new(redis_options) }
+    end
+
+    subject do
+      described_class.new(pool) { |client| Flipper::Adapters::Redis.new(client) }
+    end
+
+    it_should_behave_like 'a flipper adapter'
+
+    it "should reset the cache when the pool is reloaded or shutdown" do
+      subject.get_all
+      expect { pool.reload { |_| } }.to change { subject.pool.instance_variable_get(:@instances).size }.from(1).to(0)
+      subject.get_all
+      expect { pool.shutdown { |_| } }.to change { subject.pool.instance_variable_get(:@instances).size }.from(1).to(0)
+    end
+  end
+
+  context "with a new pool" do
+    subject do
+      described_class.new(size: 2) { Flipper::Adapters::Redis.new(Redis.new(redis_options)) }
+    end
+
+    it_should_behave_like 'a flipper adapter'
+  end
+end